| Title of Invention | A METHOD OF REDUCING OR ELIMINATING THE TRIPEPTIDYL AMINO PEPTIDASE (TPAP) PRODUCTION FROM A TPAP PRODUCING CELL OF THE GENUS ASPERGILLUS |
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| Abstract | The present invention relates to a method of reducing or eliminating the tripeptidyl aminopeptidase (TPAP) production from a TPAP producing ceil of the genus Aspergillus, in which method a DNA sequence encoding TPAP or a part thereof essential for exhibiting TPAP activity or the TPAP promoter sequence required for the expression of TPAP from a TPAP encoding DNA sequence present in said cell are modified or inactivated so as to result in a reduced or no TPAP production from said cell. |
| Full Text | ?he present invention relates to a tripeptidyl aminopeptidase [TPAP), a DNA construct encoding the TPAP, a method of produc-.ng TPAP and methods of reducing the TPAP production in cells, .n which TPAP activity is undesired. JACKGROUND OF THE INVENTION ?ripeptidyl aminopeptidases are enzymes capable of cleaving 'ragments from unsubstituted N-termini of peptides, oligopepti-les, or proteins. Tripeptidyl aminopeptidases may be unspeci-:ic, i.e. cleaving any tripeptide sequence from the unsubstitu-:ed N-terminal end, or specific, i.e. capable of cleaving jpecific types of tripeptide sequences. tripeptidyl aminopeptidases of animal origin have been reported )reviously. For instance, Doebber et al. (1978) , Endocrinology .03: 1794-1804, disclose a tripeptidyl aminopeptidase isolated :rom bovine pituitary glands, which was shown to cleave :ripeptides from the N-terminal end of bovine growth hormone. :n Mammalian Proteases Vol. 2, Exopeptidases (AP 1986, eds. r.K. McDonald and A.J. Barrett) tripeptidyl aminopeptidases are lisclosed which are isolated from beef pituitary glands, )regnant hog ovaries and hog spleen, respectively. I bacterial tripeptidyl aminopeptidase isolated from 'treptomyces lividans 66 is described by Krieger et al., Febs setters Vol. 352, No. 3, pp 385-388, 1994. Butler et al., applied and Environmental Microbiology, August 1995, p. 3145-1150 disclose the gene encoding said peptidase and the deduced imino acid sequence. The peptidase is characterized as a serine )rotease with a pH optimum between 7.5 and 8.5. :t is well-known that the stability of microbially produced >roducts, such as enzymes or other proteins, may vary, inter alia, as a function of the method by which the product is produced and/or the origin or microbial producer of the product. A reduced stability of a microbially produced product may, e.g., be due to a reduced resistance towards heat, light or other external conditions, or may be due to the composition of the product itself. In this connection, the presence of even trace amounts of protease activity in a protein product may result in a significantly reduced stability of said product. Often, however, it is not possible to exactly identify the cause of the varying stability. SUMMARY OF THE INVENTION The present inventors have now surprisingly found that various fungal species produce TPAP and that protein products produced by these organisms may contain minor amounts of TPAP which in some cases have been found to lead to a reduced stability of these products. The present inventors have succeeded in isolating and characterizing said TPAP. It has been established that the TPAP is capable of unspecifically cleaving tripeptides from the unsubstituted N-terminus of protein products, a cleavage which in some instances may be desirable, and in other instances (e.g. when resulting in a reduced stability of a protein product comprising the TPAP) is highly undesirable. Accordingly, one object of the present invention is to provide a substantially pure tripeptidylpeptidase which may be used for cleaving peptide or protein sequences. Another object is to provide a method of producing protein products essentially free from TPAP, in particular products which are substrates for TPAP and which have a reduced stability in the presence of TPAP. In a first general aspect the present invention relates to an isolated TPAP of fungal origin. In particular, the TPAP may be obtainable from strains of the fungal species Aspergillus. In further aspects the invention relates TPAP identified by amino acid and/or DNA sequence information and/or by enzyme protein charactestics, to DNA constructs encoding the TPAP and to a DNA construct comprising a nucleotide sequence which is complemen¬tary to a sufficient part of the DNA sequence encoding TPAP to be able to hybridize to said sequence and thereby abolish the TPAP producing capability of a given host cell. In a further important aspect the invention relates to a method of reducing the TPAP production from a TPAP producing cell, in which method a DNA sequence present in said cell and necessary for expression of TPAP is modified or inactivated so as to result in a reduced TPAP production from said cell. DEFINITIONS In the present context the term "TPAP" is intended to indicate an aminopeptidase which cleaves tripeptides from the N-terminal end of a peptide or protein sequence, for instance from an extended protein sequence, e.g. found in a prohormon or a proenzyme. Expressed in a general manner the TPAP is capable of cleaving the tripeptide XYZ from the unsubstituted N-terminal amino group of a peptide or protein, wherein X, Y, Z represents any amino acid residue (i.e. selected from Ala, Arg, Asn, Asp, Cys, Gin, Glu, Gly, His, lie, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, Val) . In the TPAP substrate all of X, Y and Z may be different or identical or two of X, Y and Z may be identical. It will be understood that the TPAP of the invention is unspecific as to the amino acid sequence of the tripeptide to be cleaved. In example 7 specific examples of tripeptide products obtained from cleavage of naturally occurring peptides and proteins are given. The term "obtainable" as used about the origin of DNA sequences i^onstituting part of the DNA construct of the invention is intended to indicate that the DNA sequence in question may be isolated from nucleic acid (DNA or RNA) material of the relevant organism or may be prepared on the basis of such material. For instance, the DNA sequence may be isolated from a genomic or cDNA library prepared from the organism using procedures known in the art, or may be prepared on the basis of such material. Analogously, when used in connection with the TPAP of the invention the term "obtainable" is intended to indicate that the TPAP may be recovered from the organism in question or may be encoded by a DNA sequence obtainable from said organism and recovered from an organism expressing said DNA sequence. DETAILED DISCLOSURE OF THE INVENTION The TPAP of the invention In the course of the research leading to the present invention two different TPAPs have been isolated and characterized - one from a strain of A. niger, another from a strain of A. oryzae. The two TPAPs are contemplated to be representative examples of a generally novel class of tripeptidyl amino peptidases. Thus, in one aspect the invention relates to a TPAP which is encoded by a DNA construct comprising i) at least one of, but preferably two or more of the partial DNA sequences shown in SEQ ID Nos. 1, 2 and 3, or ii) the partial DNA sequence encoding the N-terminal part of a mature TPAP present in DSM 9570, or iii) a nucleotide sequence which hybridizes to an oligonucle¬otide probe prepared on the basis of the DNA sequences shown in SEQ ID No. 1, 2 or 3 or on the basis of any of the amino acid sequences shown in SEQ ID Nos. 4-14, and which encodes a TPAP. k more detailed explanation of the nucleotide sequence iii) is given futher below in the section entitled "The DNA construct and vector of the invention". En another aspect the invention relates to a substantially pure rPAP which has one or more of the following characteristics - a capability of cleaving the substrate Phe-Pro-Ala-pNA, - a molecular weight of about 65 kDa (determined essentially as described by Laemmli, U.K., 1970, "Cleavage of structural proteins during the assembly of the head of bacteriophage T4"., Nature, 227, p. 680-685) - a pi in the range of 4-6 - a pH optimum in the range of about 5.0-7.5, - is immunologically cross-reactive with the purified A. niger TPAP or the purified A. oryzae TPAP, - comprises the N-terminal sequence Ala-Xaa(1)-Asn-Xaa(2)-Ser-His-Cys-Asp-Ser-Ile-Ile-Thr-Pro-Xaa (3) -Cys-Leu-Lys-Xaa (4) -Leu-Tyr-Asn-Ile-Gly-Asp-Tyr-Gln-Ala-Asp-Xaa(5)-Xaa(6) (SEQ ID NO 15), in which any one of Xaa(l), Xaa(2), Xaa(3), Xaa(4), Xaa(5) and Xaa(6) may be different or identical and selected from any of the naturally occurring amino acid residues. Preferably, Xaa(l) is Lys or Gin, Xaa(2) is lie or Thr, Xaa(3) is Pro or His, Xaa(4) is Glu or Gin, Xaa(5) is Pro or Ala and/or Xaa(6) is Lys or Asn. Antibodies to be used in determining immunological cross-reactivity may be prepared by use of the purified TPAP. More specifically, antiserum against the enzyme of the invention may be raised by immunizing rabbits (or other rodents) according to the procedure described by N. Axelsen et al. in: A Manual of Quantitative Immunoelectrophoresis. Blackwell Scientific Publications, 1973, Chapter 23, or A. Johnstone and R. Thorpe, Immunochemistry in Practice. Blackwell Scientific Publications, 1982 (more specifically pp. 27-31). Purified immunoglobulins nay be obtained from the antisera, for example by salt precipi¬tation [(NH4)2S04], followed by dialysis and ion exchange chromatography, e.g. on DEAE-Sephadex™. Immunochemical charac-:erization of proteins may be done either by Outcherlony iouble-diffusion analysis (O. Ouchterlony in: Handbook of Sxperimental Immunology (D.M. Weir, Ed.), Blackwell Scientific Publications, 1967, pp. 655-706), by crossed immunoelectropho-•esis (N. Axelsen et al.. supra, Chapters 3 and 4) , or by •ocket immunoelectrophoresis (N. Axelsen et al. . supra, Chapter i). In one embodiment the TPAP of the invention comprises at least one of the partial amino acid sequences shown in SEQ ID Nos. 4-9 and/or has a pH optimum of about 5.0-5.5 and/or a pi of about 5.1 or 5.2. In another embodiment the TPAP of the invention comprises at least one of the partial amino acid sequences SEQ ID NOs 10-14 and/or has a pH optimum in the range of about 5.5-7.5 and/or a pl of about 4.5. The TPAP which is encoded by a DNA sequence comprising at least one of the sequences shown in SEQ ID NO 1, 2 and 3 or the one harboured in DSM 9570 or which comprises the peptides shown in SEQ ID NOs 4-9 was isolated from a protein product produced by a strain of A. niger (cf. Example 1 hereinafter). The TPA comprising the peptides SEQ ID Nos 10-14 was isolated from a strain of A. oryzae, cf Example 2 hereinafter. Et is presently believed that a TPAP belonging to the generally lovel class of tripeptidyl aminopeptides defined herein may be 3f any origin, including animal or plant origin, but preferably Ls of microbial, i.e. bacterial or fungal, origin. As far as :he present inventors are aware the present disclosure is the :irst report on TPAP of fungal origin. TPAP of the invention lay be purified from strains which are natural TPAP producers, )r may more conveniently be produced by means of recombinant )NA techniques as a homologous or heterologous gene product as rill be further explained below. n particular, the TPAP of the invention may be obtainable from a strain of Aspergillus, such as a strain of A. oryzae, A. niger, A. japonicus, A. aculeatus, A. nidulans or A. foetidus or a strain of Trichoderma, e.g. T. viride, T. reesei, T. longibrachiatum or T. harzianum, or a species of Fusarium, e.g. F. oxysporum, F. graminearum or F. solani, or a strain of Thermomyces, e.g. T. lanuginosus or T. insolens. ^^«4. wjL .-lie invention IS preferably provided in an isolated and substantially pure form, e.g. at least 90% pure such as at least 95% pure. While the presence of TPAP in protein products may be con¬sidered undesirable due to the resulting reduced stability of said product, the use of the purified TPAP of the invention for controlled destabilization of protein products may be advan¬tageous. For instance, it is contemplated that the purified TPAP of the invention may be used for deactivation of enzymes after they have exerted their desired effect, and thus function as a "killer enzyme". Such deactivation is conventionally accomplished by thermoinactivation (or alternatively, the undesired enzyme activity is removed by purification). The use of TPAP for destabilization of thermophilic enzymes may be particularly advantageous. As an example of this use may be mentioned the deactivation of AMG used for starch liquefaction, which is presently performed by heating the reaction mixture to high temperatures (80-85°C). This deactivation may, e.g., be obtained by adding TPAP, preferably in a batch proces after AMG has hydrolyzed dextrins to glucose. A thermoinactivation of AMG is then possible by increasing the temperature to only about 66°C for a short time. Another example is the deactivation of AMG used in the fermen¬tation of beer such as low calorie beer. In the normal beer fermentation procedure AMG is inactivated by pasteurization. The addition of TPAP may reduce the thermostability of the used ?^G and thus reduce the temperature for the pasterization. By this treatment the organoleptic characteristics may be improved. Furthermore, the purified TPAP of the invention may be useful for a number of purposes in which a specific cleavage of tripeptide sequences are desirable. For instance, some proteins or peptides are synthesized in the form of precursors compris¬ing a number of additional amino acid residues on the N- terminal amino acid residue, the presence of which is undesir¬able for the protein to be used. This may, e.g., be in the pro-cessesing of proteins or peptides, which may be synthesized in protected form as precursor proteins. The DNA construct and vector of the invention In accordance with a still further aspect, the invention relates to a DNA construct encoding a TPAP, which comprises i) at least one of, but preferably two or all of the partial DNA sequences shown in SEQ ID Nos. 1, 2 and 3, or ii) the partial DNA sequence encoding the N-terminal part of TPAP and present in DSM 9570, or iii) a nucleotide sequence which hybridizes to an oligonucle¬otide probe prepared on the basis of any of the DNA sequences shown in SEQ ID No. 1, 2 or 3 or on the basis of any of the amino acid sequences shown in SEQ ID Nos. 4-14, and which encodes a TPAP, or iv) a nucleotide sequence complementary to the DNA/nucleotide sequence of i), ii) or iii). The DNA construct of the invention may be used either for the recombinant production of TPAP (DNA/nucleotide sequences i) -iii)) or for reducing the TPAP producing capability of a cell, in which said production is undesired (nucleotide sequence iv)). The nucleotide sequence iii) may, e.g., be isolated from another or related (e.g. the same) organism known or contem¬plated to produce TPAP on the basis of any of the partial DNA or partial amino acid sequences shown in SEQ ID Nos. 1-14 or the partial TPAP encoding DNA sequence of DSM 9570, e.g. using the procedures described herein, or constructed on the basis of any of said DNA or amino acid sequences, e.g. by introduction of nucleotide substitutions which do not give rise to another amino acid sequence of the TPAP encoded by the DNA sequence, but which correspond to the codon usage of the host organism intended for production of the TPAP, or by introduction of iiuuij-fejotiae substitutions which do give rise to a different amino acid sequence and therefore, possibly, a different protein structure which might give rise to a TPAP mutant with different properties than the native TPAP, but with the TPAP activity intact, other examples of possible modifications are insertion of one or more nucleotides into the sequence, addition of one or more nucleotides at either end of the sequence, or deletion of one or more nucleotides at either end or within the sequence. It will be understood that the DNA sequences shown in SEQ ID Nos. 1-3 and the DNA sequence of DSM 9570 are partial sequences which may be included in and used for isolating an entire TPAP encoding DNA sequence. This may easily be achieved by methods known in the art. In accordance with the present invention, the nucleotide sequence iii) is intended to include said entire DNA sequence. The hybridization referred to above is intended to indicate that the nucleotide sequence iii) hybridizes to the same probe as the DNA sequence encoding the TPAP (or to said DNA sequence sncoding TPAP) under certain specified conditions which are iescribed in detail in the Materials and Methods section her-sinafter. Normally, the nucleotide sequence iii) is highly homologous to the DNA sequence shown in SEQ ID No. 1, 2 or 3 or :he TPAP encoding DNA sequence of DSM 9570 (when comparing the )art of the nucleotide sequence iii) which corresponds to the )artial DNA sequence(s) disclosed herein), such as at least )5%, e.g. at least 70% homologous to said DNA sequence, e.g. at .east 75%, at least 80%, at least 85%, at least 90% or even at .east 95% homologous to any or all of said sequences. Corre-ipondingly, the TPAP of the invention is comtemplated to be at east 65%, e.g. at least 70% homologous to the amino acid ;equence encoded by said DNA sequence(s) (as evaluated on the >asis of a comparison between the part of the TPAP amino acid lequence corresponding to the part encoded by the DNA sequence n question), e.g. at least 75%, at least 80%, at least 85%, at east 90% or even at least 95% homologous. The nucleotide sequence iii) may be a DNA or an RNA sequence. The DNA sequences i)-iii) of the DNA construct of the invention may be prepared by well-known methods. Thus, the relevant DNA sequence may, for instance, be isolated by establishing a cDNA or genomic library from an organism expected to harbour the sequence, e.g. a cell as described above, and screening for positive clones by conventional procedures. Examples of such procedures are hybridization to suitable oligonucleotide probes in accordance with standard techniques (cf. Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor, New York 1989), and/or selection for clones expressing the relevant activity, and/or selection for clones producing a protein which is reactive with an antibody raised against the relevant enzyme. A preferred method of isolating a DNA sequence from a cDNA or genomic library is by use of polymerase chain reaction (PCR) using degenerate oligonucleotide probes. For instance, the PCR may be carried out using the techniques described in PCR Protocols 1993, ed. Bruce A. White and The polymerase chain reaction, 1994, ed. Kary B. Mullis. Alternatively, the DNA sequences i) and ii) may simply be isolated from DSM 9570. Furthermore, DNA sequences of the DNA construct of the inven¬tion, e.g. the nucleotide sequence iv) being complementary to the DNA/nucleotide sequence i) , ii) or iii), may be synthesized by established techniques, e.g. based on the principles disclosed by Narang, SA, 1983, Tetrahedron 39:3 and Itakura et al., 1984, Annu. Rev. Biochem. 53:323. The DNA construct may be of mixed genomic and synthetic, mixed synthetic and cDNA or mixed genomic and cDNA origin prepared by ligating fragments of synthetic, genomic or cDNA origin (as appropriate), the fragments corresponding to various parts of the entire recombinant DNA molecule, in accordance with standard techniques. It will be understood that a preferred use of the DNA sequence i) , ii) or iii) is in the preparation of recombinant TPAP, whereas a preferred use of the DNA sequence iv) is for the reduction of the TPAP producing capability of cells intended for use in the production of protein products which are sensible to TPAP. Although the DNA sequence iv) may be complementary to the entire TPAP encoding sequence, it is normally sufficient that the DNA sequence iv) is complementary to only part of said sequence. Expressed in a functional manner, the DNA sequence iv) must be complementary to a sufficient length of the DNA sequence encoding the TPAP to allow for hybridization to the TPAP encoding DNA and thus reduction or prohibition of the transcription of said mRNA. Typically, it is sufficient that the DNA sequence iv) comprises a DNA fragment of at least 17 nucleotides such as at least 3 00 nucleotides. The vector carrying a DNA construct of the invention, preferab¬ly a recombinant expression vector, may be any vector which may conveniently be subjected to recombinant DNA procedures, and the choice of expression vector will often depend on the host cell into which it is to be introduced. Thus, the vector may be an autonomously replicating vector, i.e. a vector which exists as an extrachromosomal entity, the replication of which is independent of chromosomal replication, e.g. a plasmid or a bacteriophage. Alternatively, the vector may be one which, when Introduced into a host cell, is integrated into the host cell jenome and replicated together with the chromosome(s) into [n the DNA construct or the vector, the DNA sequence should be jperably connected to a suitable promoter sequence. The pro~ aoter may be any DNA sequence which shows transcriptional ac-:ivity in the host cell of choice and may be derived from genes encoding proteins either homologous or heterologous to the host cell. The promoter may be derived from genes encoding both ex¬tracellular and intracellular proteins, such as amylases, glucoamylases, proteases, lipases, cellulases and glycolytic enzymes. Examples of suitable promoters for directing the tran¬scription of the DNA construct of the invention are promoters derived from genes for A. oryzae TAKA amylase, Rhizomucor miehei aspartic proteinase, A. niger glucoamylase, A. niger neutral a-amylase, A. niger acid stable a-amylase, and Rhizomu¬cor miehei lipase. Examples of promoters from genes for glycolytic enzymes are TPI, ADH, and PGK. The promoter may also be a homologous promoter, i.e. a gene native to the host strain being used. The promoter sequence may be provided with linkers for the purpose of introducing specific restriction sites facilitating ligation of the promoter sequence with the gene of choice or tfith a selected signal peptide or preregion. The DNA construct and/or expression vector of the invention may ilso comprise a suitable terminator operably connected to the )NA sequence encoding the TPAP and/or a polyadenylation sequence. The terminator and polyadenylation sequences may be ierived from the same sources as the promoters. Enhancer sequences may also be inserted into the construct. ?he DNA construct and/or vector may further comprise a DNA sequence enabling the vector to replicate in the host cell in [uestion. Examples of such sequences are the origins of repli-•.ation of plasmids pUC19, pACYC177, pUBllO, pE194, pAMBl and >IJ702. 'he DNA construct and/or vector may also comprise a selectable larker. Examples of selection markers include the amdS or argB, rpC or pyrG (the latter three markers, e.g. from A. nidulans r A. niger). The procedure used to construct the DNA construct of the invention comprise ligating the DNA sequences mentioned above the promoter, the terminator and other elements, respectively, and to insert it into suitable vectors containing the informa¬tion necessary for replication, are well known to persons skilled in the art (cf., for instance, Sambrook et al. op. cit.) . The cell and a method of producing TPAP of the invention In one embodiment the cell of the invention either comprising a DNA construct or an expression vector of the invention as defined above is used as a host cell in the recombinant produc¬tion of TPAP of the invention. In this case the DNA construct or expression vector comprises any of the TPAP encoding DNA sequences i)-iii) or the insert of DSM 9570 defined above. The 3ell may be transformed with the DNA construct, conveniently by Integrating the DNA construct in the host chromosome, although :he DNA construct may also exist as an extrachromosomal entity, lowever, the integration is generally considered to be an idvantage as the DNA sequence is more likely to be stably main-:ained in the cell. Integration of the DNA constructs into the lost chromosome may be performed according to conventional lethods, e.g. by homologous recombination. Alternatively, the lell may be transformed with an expression vector as described telow in connection with the different types of host cells. he cell of the invention may be a cell of a higher organism uch as a mammal or an insect, but is preferably a microbial ell, e.g. a bacterial or a fungal (including yeast) cell. xamples of suitable bacteria are grampositive bacteria such as acillus subtilis, Bacillus licheniformis, Bacillus lentus, acillus brevis, Bacillus stearothermophilus, Bacillus alkalo-hilus, Bacillus amyloliquefaciens, Bacillus coagulans, Bacil-us circulans, Bacillus lautus, Bacillus thuringiensis or treptomyces lividans or Streptomyces murinus, or gramnegative acteria such as E.coli. The transformation of the bacteria may for instance be effected by protoplast transformation or by using competent cells in a manner known per se. The yeast organism may favourably be selected from a species of Saccharomyces or Schizosaccharomyces, e.g. Saccharomyces ce-revisiae. The filamentous fungus may advantageously belong to a species of Aspergillus, e.g. Aspergillus oryzae, A. nldulans, A. foetidus, A. aculeatus, A. japonicus or A. niger, a species of Trichoderma, e.g. T. reesei, T. longibrachiatum or T. harzianum, or a species of Fusarium, e.g. F. oxysporum, F. graminearum or F. solani. Fungal cells may be transformed by a process involving protoplast formation and transformation of the protoplasts followed by regeneration of the cell wall in a manner known per se. In a further aspect the invention relates to a method of producing TPAP, which method comprises L) culturing a cell of the invention as defined above in a suitable culture medium under conditions permitting expression 3f the TPAP, and recovering the TPAP from the culture. [•he medium used to cultivate the cells may be any conventional ledium suitable for growing the host cell in question. Suitable ledia are available from commercial suppliers or may be >repared according to published recipes (e.g. in catalogues of •.he American Type Culture Collection) . It is believed that the >resence of protein in the medium may result in an increased 'PAP production. 'he TPAP may be recovered from the medium by conventional irocedures including separating the cells from the medium by lentrifugation or filtration, if necessary after disruption of he cells, precipitating the proteinaceous components of the upernatant or filtrate by means of a salt, e.g. ammonium sul-hate, followed by purification by a variety of chromatographic rocedures, e.g. ion exchange chromatography, affinity chroma-ography, or the like. Removal or reduction of TPAP activity The identification of TPAP as a destabilizing factor in microbially produced protein products may have important consequences for the production of a large number of different protein products. Thus, as it has been demonstrated by the present inventors, even minor amounts of TPAP present in a protein product may result in a reduced thermostability of said product. Accordingly, by the present invention it is possible to construct production strains which have a reduced TPAP-producing capability. The reduction of TPAP production from a TPAP producing cell may conveniently be accomplished by modification or inactivation of a DNA sequence present in said cell and necessary for express¬ion of TPAP so as to result in a reduced TPAP production from said cell. The DNA sequence to be modified may, e.g., be a DNA sequence encoding TPAP or a part thereof essential for exhibiting TPAP activity or may be a regulatory sequence required for the expression of TPAP from a TPAP encoding DNA sequence. As an example the regulatory sequence may be a promoter sequence or a functional part thereof, i.e. a part which is sufficient for effecting expression of TPAP. The modification or inactivation of the DNA sequence may be performed by subjecting the TPAP producing cell to mutagenesis and selecting for cells for which the TPAP producing capability las been reduced. The mutagenesis, which may be specific or random, may, e.g., be performed by use of a suitable physical 3r chemical mutagenizing agent, by use of a suitable oligonu¬cleotide, or by subjecting the DNA sequence to PCR generated nutagenesis. Furthermore, the mutagenesis may be performed by ise of any combination of these mutagenizing agents. Examples of a physical or chemical mutagenizing agent suitable for the present purpose includes ultraviolet (UV) irradiation, hydroxylamine, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), O-methyl hydroxylamine, nitrous acid, ethyl methane sulphonate (EMS), sodium bisulphite, formic acid, and nucleotide analo¬gues. When such agents are used the mutagenesis is typically per¬formed by incubating the cell to be mutagenized in the presence of the mutagenizing agent of choice under suitable conditions for the mutagenesis to take place, and selecting for mutated cells having a reduced TPAP production. When the modification or inactivation is accomplished by introduction, substitution or removal of one or more nucleo¬tides in the TPAP encoding sequence or a regulatory element required for the transcription or translation thereof, nucleo¬tides may, e.g., be inserted or removed so as to result in the Introduction of a stop codon, the removal of the start codon or a change of the open reading frame. The modification or Lnactivation of the TPAP encoding sequence or a regulatory element may be accomplished by site-directed mutagenesis or PCR generated mutagenesis in accordance with methods known in the irt. Although in principle, the modification may be performed :n vivo, i.e. directly on the cell carrying the TPAP gene to be lodified, it is presently preferred to conduct the modification .n vitro as exemplified below. in example of a convenient way to inactivate or reduce the TPAP (reduction of a host cell of choice is based on the principles »f gene replacement or gene interruption. For instance, the [ene interruption method involves the use of a DNA sequence lorresponding to the endogenous gene or gene fragment which it s desired to destroy. Said DNA sequence is in vitro mutated to defective gene and transformed into the host cell. By omologous recombination the defective gene replaces the ndogenous gene or gene fragment. It may be desirable that the efective gene or gene fragment encodes a marker which may be used for selection of transformants in which the TPAP gene has been modified or destroyed. Alternatively, the modification or inactivation of the DNA sequence may be performed by use of established anti-sense techniques using a nucleotide sequence complementary to the TPAP encoding sequence, e.g. the nucleotide sequence iv) described above. More specifically, the TPAP production from a TPAP producing cell may be reduced or eliminated by introducing a nucleotide sequence complementary to the TPAP encoding sequence and thus capable of hybridizing to TPAP mRNA produced in the cell into the cell in such a manner that the nucleotide sequence may be transcribed in the cell under conditions allowing the nucleotide sequence to hybridize to the TPAP mRNA ind thus reduce the amount of TPAP translated from said mRNA or Jliminate any such translation. [•he TPAP-deficient mutants so created are particularly useful Ln the expression of heterologous proteins. In the present jontext the term "heterologous proteins" is intended to mean a >rotein which is not native to the host cell, a native protein .n which modifications have been made to alter the native ;equence, or a native protein whose expression is quantitative-y altered as a result of a manipulation of the host cell by ecombinant DNA techniques. t is preferred that the TPAP producing cell to be modified in ccordance with the present invention is a strain which is uitable for the production of desired protein products, either omologous or heterologous to the cell. For instance, cells of he fungal genera Aspergillus, Trichoderma and Fusarium are xamples of prefered production cells. Accordingly, the cell to e modified according to the present invention is preferable a ell of an Aspergillus sp., in particular a cell of A. niger, . oryzae, A. japonicus, A. foetidus or A. nidulans or a cell f a Trichoderma sp., e.g. T. reesei, T. longibrachiatum or T. arzianum, or a cell of a Fusarium sp., e.g. F. oxysporum, F. raminearum or F. solani. in a specific embodiment of the invention the cell to be modified is a cell of A. niger or A. oryzae which is used for the production of enzymes such as AMG. In a further aspect the invention relates to a method of preparing a product essentially free from TPAP activity, which method comprises transforming a host cell as described above having a reduced or no TPAP producing capability with a DNA sequence encoding the product, culturing the transformed cell under suitable conditions for expression of the product, and recovering the product from the culture. In an alternativ aspect the invention relates to a method of preparing a product essentially free from TPAP activity, which product is encoded by a DNA sequence present in a TPAP express¬ing cell, which method comprises modifying or inactivation a DNA sequence present in said cell and necessary for expression 3f TPAP as described above, and subsequently culturing the cell ander suitable conditions for expression of the product, and recovering the product from the culture. [n a still further aspect the invention relates to a method of jreparing a product essentially free from TPAP by fermentation )f a TPAP-producing cell which also produces the product, which lethod comprises adding an effective amount of an inhibitor :apable of inhibiting TPAP activity to the fermentation broth iither during or after the fermentation has been completed, •ecovering the product of interest from the fermentation broth, md optionally subjecting the recovered product to further turification. This method is further illustrated in the ixamples below. n a still further alternative aspect the invention relates to . method of preparing a product essentially free from TPAP ctivity, which product is encoded by a DNA sequence present in TPAP expressing cell, which method comprises cultivating the PAP expressing cell encoding the product under conditions ermitting the expression of the product, subjecting the resulting culture broth to a combined pH and temperature treatment so as to reduce the TPAP activity substantially, and recovering the product from the culture broth. Alternatively, the combined pH and temperature treatment may be performed on an enzyme preparation recovered from the culture broth. The combined pH and temperature treatment may optionally be used in combination with a treatment with a TPAP inhibitor. In accordance with this aspect of the invention it is possible to remove at least 60% of the TPAP activity, such as at least 75% of the activity, more preferably at least 85% of the activity, still more preferably at least 95% of the activity, and most preferably essentially at least 99% of the TPAP activity. It is contemplated that a complete removal of TPAP activity may be obtained by use of this method. The combined pH and temperature treatment is preferably carried out at a pH in the range of 6.5-7 and a temperature in the range of 25-40°C for a sufficient period of time for obtaining the desired effect. Typically, 0.5-1 hour is sufficient for obtaining the desired effect. The methods used for cultivation and purification of the product of interest may be performed by methods known in the art, e.g. as described herein before. The methods of the invention for producing an essentially TPAP-free product is of particular interest in the production of eukaryotic proteins, in particular fungal proteins such as enzymes. The enzyme product may, e.g., be selected from an amylolytic enzyme, a lipolytic enzyme, a proteolytic enzyme, a cellulytic enzyme, an oxidoreductase or a plant cell-wall degrading enzyme. Examples of such enzymes include AMG, amylase, lipase, cutinase, esterase, cellulase, hemicellulase, protease, peroxidase, laccase, phenoloxidase, catalase, glucose oxidase, phytase, lyase, pectinase, glucosidase, mannosidase, isomerase, invertase, trasferase, ribonuclease, galactosidase, transglutaminase and chitinase. The TPAP-deficient cells may also be used to express heterologous proteins of pharmaceutical interest such as hormones, growth factors, receptors, and the like. It will be understood that the term "eukaryotic proteins" is intended to include not only native proteins, but also those proteins (e.g. enzymes) which have been modified by amino acid substitutions, deletions, additions, or other modifications which may be made to enhance activity, thermostability, pH tolerance and the like. In a further aspect the invention relates to a protein product essentially free from TPAP activity which is produced by the method of the invention. EXAMPLE 1 PURIFICATION AND CHARACTERIZATION OF A. niger TPAP Haterials and methods Phe-Pro-Ala-pNA sul^strate (available from Bachem, Switzerland) . Protease inhibitors Ma-Ala-Phe-chloromethyIketone 3enzyloxycarbonyl-Ala-Pro-Phe-chloromethylketone 3enzyloxycarbonyl-Gly-Gly-Phe-chloromethyl-ketone. ?urification of TPAP PPAP was purified from a commercial A. niger AMG preparation [available from Novo Nordisk A/S, Denmark). A sample of 300 ml formulated AMG product was repeatedly diluted and concentrated it 4'C in a Filtron® concentrator equipped with a 3 kDa cutoff lembrane until the conductivity was less than 1.5 mS/cm. All )ther purification steps were carried out at ambient tempera-:ure. Cation exchange chromatography employing a HaCl gradient The concentrate (600 ml) was adjusted to pH 4.0 and filtrated before application to a 200 ml (2.6 x 37 cm) S-Sepharose column equilibrated with 20 nM sodium acetate, pH 4.0. A flow of 10 ml/min was used. The TPAP was eluted with a linear NaCl gradient from 0 to 0.2 M in 10 column volumes. One pool con¬taining the largest part of the peptidase activity was made. A buffer change to 20 mM sodium acetate, pH 5.5 was made in an Amicon cell equipped with a Diaflo membrane with a cutoff of 10 kDa. Anion exhange chromatography The pool from the S-Sepharose column was further purified on a HiLoad Q-Sepharose HP column (50 ml, 2.6 x 10 cm) equilibrated with 20 mM sodium acetate, pH 5.5. Elution of TPAP was per¬formed with a linear NaCl gradient from 0 to 0.5 M in 15 column volumes. The protein was applied with a flow of 8.0 ml/min and eluted with 5.0 ml/min. A pool containing the largest part of TPAP was made. A buffer change to 20 mM sodium acetate, pH 4.0 was made in an Amicon cell as described above. Cation exchange chromatography employing a PH gradient The pool from the HiLoad Q-Sepharose HP column was finally pur if ied on a Mono S column (5/ 5) equi librated with 20 mM sodium acetate, pH 4.0. A gradient from pH 4.0 to pH 6.0 was made in 30 column volumes using 20 mM sodium acetate, pH 4.0 and 20 raM sodium acetate, pH 6.0. The flow was 1.0 ml/min. Two isoenzymes of TPAP eluted at pH 5.1 and 5.2, respectively. Furificatiott of AHG AMG Gl has been purified from a commercial AMG preparation (Novo Nordisk A/S) by anion exchange chromatography using Q-Sepharose. A 50 ml column was equilibrated with 20 mM sodium acetate, pH 5.5 and the Gl form eluted with a linear NaCl gradient from 0 to 0.6 M NaCl in 8 column volumes. The flow was 8.0 ml/min. AMG, was purified after TPAP treatment of AMG Gl on a Mono Q column equilibrated with 20 nM sodium acetate, pH 4.3. A linear NaCl gradient from 0 to 1.0 M in 30 column volumes was used for elution. The flow was 1.0 ml/min. Destabilization assay Aliquots of purified AMG Gl were incubated with different mixtures of TPAP and buffer in O.i M sodium acetate, pH 4.3 for several weeks at 37C. The final volume was either 1 or 2 ml with a concentration of AMG Gl of 10 AGU/ml. 100 Ml of the incubation mixture were withdrawn and diluted to 2 AGU/ml with 0.1 M sodium acetate, pH 4.3. A heat treatment at 65°C for 30 min was carried out on the diluted sample. After cooling the samples to ambient temperature, the activity of untreated and heat treated samples were measured in microtiter plates using the chroinogenic substrate p-nitrophenyl-a-D-glycopyranoside (pNPG) (Merck, Art. 6792). 50 ^1 3 mM pNPG in 0,1 M sodium acetate, pH 4.3 was incubated with 25 ^i sample for 30 min at ambient temperature. The reaction was stopped by addition of 75 µ1 0.1 M sodium tetraborate. The absorbance at 405 nm was measured in a UV-max kinetic microplate reader. T30 was cal¬culated as the percentage of activity retained after heat -treatment. All measurements were made in duplicate. TPAP assay The assay was performed either in a microtiter plate reader or in a spectrophotometer using a substrate concentration of 0.2 mM Phe-Pro-Ala-pNA in 0.1 M sodium acetate buffer, pH 4.3. A 5 mM stock solution of Phe-Pro-Ala-pNA was made in DMSO and diluted before use. The reaction was followed for 4 min at 405 nm either in a UV-max kinetic microplate reader or a spectrophotometer and the initial rate of cleavage calculated. inhibition of TPAP Aliquots containing 4 ng TPAP were incubated with a number of protease inhibitors: 1 mM Ala-Ala-Phe-chloromethylketone, l mM benzyloxycarbonyl-Ala-Pro-Phe-chloromethylketone and 1 mM ben- zyloxycarbonyl-Gly-Gly-Phe-chloroinethyl-ketone. Following 30 min incubation the residual activity was determined. Storage stability of filtrated fermentation broths The culture broths were centrifuged and sterile filtrated through a o. 22 [MTR filter. The broths were made 0.1% with respect to potassium sorbate and sodium benzoate and pH was adjusted to 4.3. Aliguots of 2 ml were either added 200 µ1 of 10 mM Ala-Ala-Phe-chloromethylketone or 200 µ1 of 0.1 M sodium acetate, pH 4.3. Samples were withdrawn and diluted to 2 AGU/ml before the T30 determination as described above. Determination of AMG activity (AGO) AMG activity was determined as described By K.A. Holm, 1980, Anal. Chem. Acta., 117, pp 359-362. In brief, the method is based on hydrolysis of maltose by AMG under formation of alpha-D-glucose. After a short, continuous dialysing procedure the concentration of glucose is determined by a glucose dehydroge¬nase (GlucDH) reaction (performed at pH 7.6). Standard condi¬tions for the automated Auto-Analyzer method are: substrate: maltose 28 mM Incubation buffer: acetate O.IM, pH 4.3 Incubation temperature: 37'C Incubation time: 5 min. The enzyme-working area of the method is 0.5-4 AGU/ml. Results TPAP was purified to homogeniety from a commercial AMG prepara¬tion (Novo Nordisk A/S) according to the purification scheme shown in Table 1. The elution profile from the final cation exchange column revealed the presence of two isoenzymes of TPAP (TPAP-I and TPAP-II) with pi 5.1 and 5.2, respectively. Both isoforms were pure as judged by SDS-PAGE and N-terminal sequencing, but the specific activities of the enzymes differed (of. Table 1). TPAP-II had 20% higher specific activity than TPAP-I. A deamidation of one or several Asn- or Gin-residues either in the fermentation broth or during purification can explain the small difference in pI between the two isoforms of TPAP. pH optimum The pH optimum of TPAP was determined using the same procedure as in the TPAP assay described above. 0.1 M acetate buffer was used to regulate the pH, The resulting pH optimum curve is shown in Fig. 1. It is seen that the TPAP functions optimally at a pH in the range of 5.0-5.5, in particular 5.25. Determination of temperature optimum for TPAP The temperature/activity relationship of TPAP was determined in 0,1 M sodium acetate buffer, pH 5.5 using the TPAP assay described above. As can be seen from the table TPAP has maximal activity in the temperature range 45-55 °C. Mass spectrometry Matrix assisted laser desorption ionisation time-of-flight mass spectrometry of TPAP purified from A. niger gave a broad signal indicating that the TPAP is glycosylated. The average mass was found to be 54.5 kDa. EXAMPLE 2 PURIFICATION AND CHARACTERIZATION OF A. oryzae TPAP Materials & Methods As a starting material for the purification, the supernatant of an A. oryzae IPC 4177 fermentation fermented at pH 5 in a soy containing medium was used. After fermentation, the culture broth was centrifuged to remove the majority of cells. Purification Approx. 4L supernatant was germ filtered on a Seitz EKS plate. The EKS-filtrate was ultrafiltrated on a 3k cut-off Filtron cassette (Minisette) to minimal volume. Ultrafiltrate = 240 ml. 170 ml of the ultraf iltrate was precipitated with solid ammonium sulphate (AMS) to give an AMS saturation of approx. 90%. After stirring for at least 30 min., the AMS precipitate was recovered by centrifugation in a Sorvall RC3B centrifuge (4500 rpm, 15 min., room temp) . 100 ml deionized water was added to the AMS precipitate to dissolve the protein and 1% (w/v) FGV120 activated charcoal was added to remove colour. After stirring for approx. 1 hour the suspension was filtered on a Seitz EKl plate to remove charcoal (and colour). The EKl-filtrate was dialysed against 1) 100 mM HjBO,, 10 mM dimethyl f glutaric acid, 2 niM CaClj, pH 5 and 2} deionized water. After an EKi-filtration the dialysate (260 ml) was freezed in aliquots. A 120 ml aliquot of the dialysate was thawed and applied to a 1.4L G25 Sephadex column equilibrated in 20 mM CHjCOOH/NaOH, pH 5.0. To remove colour and very acidic proteins, the G25-filtrate was applied to a 40 ml Q-sepharose FF column equilibrated in the same buffer (CHjCOOH/NaOH, pH 5.0). After washing the column, bound protein was eluted with a linear NaCl gradient (0 —> 200mM). Fractions from the column were analysed for TPAP activity. Most of the TPAP activity was seen in the run-through (70%), whereas most of the protein was bound to the column. The run-through from the Q-sepharose column was applied to a 50 ml S-sepharose HP column equilibrated in 20 mM CHjCOOH/NaOH, pH 5.0. After washing the column, bound protein was eluted with a linear NaCl gradient (0 —> 200mM). Fractions from the column were analysed for TPAP activity. Most of the TPAP activity was again seen in the run-through (75%) . The rest of the TPAP activity was in the start of the NaCl gradient. The run-through + fractions 1-11 were pooled and dialysed against 50 mM H3BO3, 5 mM dimethyl glutaric acid, l mM CaCl2, pH 6.0. After adjusting the pH of the dialysed pool to pH 7.0 the enzyme was applied to a 23 ml SOURCE Q column equilibrated in 50 mM H3BO3, 5 MM dimethyl glutaric acid, l mM CaCl^, pH 7.0. After washing the column, bound protein was eluted with a linear NaCl gradient (0 —> 500 mM). Fractions from the column were analysed for TPAP activity. All the TPAP activity was seen in the run-through (95%). The reason for this has to be, that the column had been overloaded with protein. The run-through was dialysed against 20 mM CHjCOOH/NaOH, pH 4.0. The dialysed enzyme was applied to a 50 ml S-sepharose HP column equilibrated in 20 mM CHjCOOH/NaOH, pH 4.0. After washing the column, bound protein was eluted with a NaCl gradient (0 —> 200 mM). Fractions from the column were analysed for TPAP activity. The TPAP activity eluted with 100 mM NaCl. The TPAP activity was pooled and dialysed against 20 mM CHjCOOH/NaOH, pH 4.0. To get a better resolution than what the S-sepharose column could give, the dialysed pool was applied to an 8 ml SOURCE S column equilibrated in the same buffer (20 mM CHjCOOH/-NaOH, pH 4.0). After washing the column, bound protein was eluted with a NaCl gradient (0 —> 200 mM). Fractions from the column were analysed for TPAP activity. The TPAP activity eluted with 60 mM NaCl. The TPAP activity was pooled and dialysed against 20 mM CHsCOOH/NaOH, pH 5.5. The dialysed enzyme was applied to a 23 ml SOURCE Q column equilibrated in 20 mM CH3COOH/NaOH, pH 5.5. After washing the column, bound protein was eluted with a NaCl gradient (0 —> 200 mM) . The TPAP activity eluted with 30 mM NaCl. Fractions from the column were analysed by SDS-PAGE and for TPAP activ¬ity. The SDS-PAGE gel showed that the fractions containing TPAP activity contained two major bands: a 65 kDa band (TPAP) and a 3 0 kDa band. The TPAP band was diffuse whereas the 30 kDa band was sharp, indicating that TPAP is glycosylated whereas the 30 kDa band is not. The TPAP containing fractions were concentrated to 1 ml by ultrafiltration and applied to a 150 ml Sephacryl S-loo column equilibrated in 20 mM Tris-acetate, 100 mM NaCl, pH 5.5. With a 1.0 ml/min flow rate the two bands were separated. The TPAP activity containing fractions were pooled as A.oryzae TPAP. Mass spectrometry Matrix assisted laser desorption ionisation time-of-flight mass spectrometry of TPAP purified from A. oryzae gave a broad signal indicating that the TPAP is glycosylated. The average mass was found to be 55.0 kDa. pH profile of A. oryzae TPAP The pH dependency of the activity of TPAP from A. oryzae was investigated using the chromogenic substrate Phe-Pro-Ala-pNA. To 50 µ1 of enzyme 150 µl Britton-Robinson buffer at the indicated pH were added before incubation with 50 /il Phe-Pro-Ala-pNA at a final substrate concentration of 0.2 mM. The assays were performed in an UV-max kinetic microtiter plate reader and the reaction followed for 3.5 min at 405 nm. The relative activity (RA) is given in the table 3 below. EXAMPLE 3 Peptide sequences of A. ni(jer TPAP N-terminal amino acid sequencing of intact A. niger TPAP forms I and II (Example 1) as well as of peptides derived from TPAP form I was performed in an Applied Biosystems 473A sequencer operated according to the manufacturers instructions. The N-terminal amino acid sequences of intact TPAP forms I and II were determined for 30 residues. The two sequences were identical and found to be: Ala-Gln-Asn-Thr-Ser-His-Cys-Asp-Ser-Ile-Ile-Thr-Pro-His-Cys-Leu-Lys-Gln-Leu-Tyr-Asn-Ile-Gly-Asp-Tyr-Gln-Ala-Asp-Pro-Lys-(SEQ ID No, 4) The sequence did not show any homology to other proteins. Following denaturation, reduction and s-carboxymethylation, peptides were derived from TPAP form I by proteolytic cleavage using the lysyl-specific protease froro Achromobactex-. The resulting peptides were fractionated and repurified using revesed phase HPLC. The purity and mass of the peptides were evaluated using matrix assisted laser desorption ionisation time-of-flight mass spectrometry using a VG Analytical TofSpec operated according to the manufacturers recommandations. The following 7 peptides were sequenced. Peptide 1: Ala-Gln-Asn-Thr-Ser-His-Cys-Asp-Ser-Ile-Ile-Thr-Pro-His-Cys-Leu-Lys Asn3 is glycosylated as shown by mass spectrometry and amino acid sequencing. Peptide 1 is identical to amino acid residues 1-17 of intact TPAP and thus of the sequence shown in SEQ ID No. 4. Peptide 2: Gln-Leu-Tyr-Asn-Ile-Gly-Asp-Tyr-Gln-Ala-Asp-Pro-Lys Peptide 2 is identical to amino acid residues 18-30 of intact TPAP (and thus of the amino acid sequence shown in SEQ ID No. 4) . Peptide 2 is recovered in two forms as revealed by mass spectrometry and amino acid sequencing. One form with an N-terminal Gin residue and one form with this Gin residue con¬verted to a pyroglutamate residue. Peptide 3: Thr-Ser-Pro-Glu-Gln-Ala-Val-Ser-Phe-Ser-Ser-Gly-Gly-Phe-Ser-Asp-Leu-Trp-Pro-Arg-Pro-Ser-Tyr-Gln-His- (SEQ ID No. 5) Peptide 4: Phe-Ser-Gly-Leu-Phe-Asn-Ala-Ser-Gly-Arg-Ala-Phe-Pro-Asp-Val-Ser-Ala-Gln-Gly-Val-Asn-Tyr-Ala-Val-Tyr-Asp-Lys fSEQ ID No. 6) Asn6 is glycosylated as shown by mass spectrometry and amino acid sequencing. Peptide 5: Ile-Gly-Phe-Ala-Ser-Tyr-Leu-Gln-Glu-Tyr-Ala-Arg-Tyr-Ala-Asx-Leu-Glu-Arg-Phe-Glu-Gln-His-Leu- (SEQ ID No. 7) It was not possible to discriminate whether Asxis was an Asp or Asn residue. Peptide 6: Xaa-Leu-Asx-Leu-Gln-Tyr-Ile-Leu-Gly-Val-Ser-Ala-Pro-Val-Pro-Ile-Thr-Glu-Tyr-Ser-Thr-Gly-Gly-Arg-Gly-Glu-Leu-Val-Pro- (SEQ ID No. 8) It was not possible to discriminate whether Asx3 was an Asp or Asn residue. Xaal was unidentified. Peptide 7: Gly-Ala-Leu-Asx-Asp-Ile-Val-Asn-Gly-Thr-Ser-Val-Gly-Gln-Asp-Gly-Arg-Asn-Arg-Phe-Gly-Gly-Thr-Pro-Asn-Gly-Ser- (SEQ ID No. 9) It was not possible to discriminate whether Asx4 was an Asp or Asn residue. Note that Asn25 is not glycosylated although it is found in the concensus sequence for N-glycosylation. Peptide sequences of A. oryzae TPAP N-terminal amino acid sequencing intact TPAP as well as of peptides derived from TPAP was carried out in an Applied Biosystems 473A protein sequencer according to the manufac¬turers instructions. The N-terminal amino acid sequence of intact TPAP were deter¬mined following SDS-PAGE and electroblotting onto a PVDF-membrane using standard procedures. The following 23 residue amino acid sequence was found: Ala-Lys-Xaa-ile-Ser-His-Yaa-Asp-Ser-Ile-Ile-Thr-Pro-Pro-Yaa-Leu-Lys-Glu-Leu-Tyr-Asn-Ile-Gly- (SEQ ID NO 14) This sequence is clearly homologous to the N-terminal amino acid sequence of TPAP from A. niger. Based on this homology Xaa most likely is a glycosylated Asn-residue while Yaa probably represents Cys-residues. Following denaturation, reduction and S-carboxymethylation, peptides were derived from TPAP by proteolytic cleavage using the lysyl-specific protease from Achromojbacter. The resulting peptides were fractionated and repurified using revesed phase HPLC. The purity and mass of the peptides were evaluated using matrix assisted laser desorption ionisation time-of-flight mass spectrometry using a VG Analytical TofSpec operated according to the manufacturers recommandations. The following 4 peptides were sequenced. Peptide 8: Glu-Leu-Tyr-Asn-Ile-Gly-Asp-Tyr-Gln-Ala-Asp-Ala-Asn-Ser-Gly-Ser-Lys (SEQ ID NO 10) This peptide overlaps with the 6 last amino acid residues determined by the N-terminal sequencing of intact TPAP thereby extending the N-terminal sequence to 34 residues. Peptide 9: Thr-Thr-Pro-Glu-Arg-Gly-Thr-Tyr-Phe-Ser-Ser-Gly-Gly-Phe-Ser-Asn-Tyr-Trp-Pro-Arg-Pro-Glu-Trp-Gln-Asn-Gln-Ala-Val-Ala-Ser-Tyr-Leu- (SEQ ID NO 11) This peptide is homologous to peptide 3 from A. niger TPAP. Peptide 10: Gly-Thr-Leu-Gly-Glu-Phe-Asp-Gly-Thr-Ser-Ala-Ser-Ala-pro-Ala-Phe-Ser-Ala-Val-Ile-Ala-Leu-Leu-Asn-Asp-Ala-Arg-Leu-Arg-Ala-Gly-Lys-Pro-Thr-Leu-Gly-Phe-Leu-Asn-Pro-Trp-Leu-Tyr-Lys (SEQ ID NO 12) Peptide 11: Thr-Gly-Arg-Gln-Gly-Leu-Gln-Asn-Ile-Thr-Leu-Gly-Ala-Ser-Ile-Gly-Xaa-Thr-Gly-Arg-Ala-Arg-Phe-Gly-Gly-Ala-Pro-Asn-Gly-Gly-Pro-Val-Val-Pro-Tyr-Ala-Ser- (SEQ ID NO 13), Xaa designates an unidentified residue. EXAMPLE 4 The amino acid compositions of A. niger TPAP forms i and II were determined. Duplicates of lyophilyzed aliqouts of TPAP forms I and II were hydrolysed in 6 N HCl containing 0.1% phenol at 110°C in vacuo for 16 h. Trypthophan was determined following hydrolysis in 3M methanesulfonic acid. Following hydrolysis the amino acid compositions were determined using an Applied Biosystems 420A amino acid analysis system operated according to the manufacturers instructions. The results show that within experimental error TPAP forms I and II have iden¬tical amino acid compositions as shown in Table 4 below. 1 h, 2 h and 4 h. Following hydrolysis the monosaccharide compositions were analysed by high performance ion exchange chromatography using a CarboPacTM PAl column eluted with 16 mM NaOH. The monosaccharides were detected by pulsed amperometric detection. Due to the different stability and release of the monosaccharides in 2 M TFA the amount of galactose was deter¬mined after 1 h hydrolysis, the amount of mannose after 2 h hydrolysis and the amount of glucosamine after 4 h hydrolysis. The results obtained indicate very minor differences in mannose content of TPAP form I and II as shown in the table below. Table 5 Monosaccharide compositions of TPAP forms I and II. The results are given in pmol monosaccharide/pmol protein as determined from amino acid analysis. EXAMPLE 6 CLEAVAGE BY A. niger TPAP The ability of A. niger TPAP to destabilize the AMG Gl form was investigated using purified AMG and TPAP (obtained as described in the Materials and Methods section in Example 1) at TPAP/AMG ratios equal to those in formulated products. Amino acid se¬quencing of the destabilized preparations revealed a modifica¬tion in the N-terminal of the catalytic domain of AMG. A tripeptide comprising the first three amino acid residues (Ala-Thr-Leu) had been cleaved off by the peptidase indicating that the enzyme is a tripeptidyl aminopeptidase. The classification I as a tripeptidyl aminopeptidase, based on the cleavage of AMG as well as of the chromogenic substrate Phe-Pro-Ala-pNA, was further supported by the lack of activity towards another chromogenic substrate Succinyl-Ala-Ala-Ala-pNA. In this substrate the free amino group at the N-terminus has been succinylated and thereby made the substrate inaccesible to cleavage by TPAP. The TPAP cleavage of the AMG batches was not complete after 3 weeks storage, as a mixture of intact and truncated AMG (AMG,nj„) was detected by amino acid sequencing. The destabilization of AMG Gl obtained with various dosages of TPAP at different temperatures has been investigated. A TPAP dosage in the range from 3 to 10 f^g/ml gave a significant destabilization of AMG and also TPAP/AMG ratios similar to those measured in several fermentations. The destabilization effect was most pronounced at 37°C but also at 25*'C a clear effect on the thermostability was observed after 27 days of storage. Storage at 4°C did not affect the thermostability of AMG. EXAMPLE 7 The specificity of A. niger TPAP was investigated using various native protein and peptide substrates. Using these substrates it was found that TPAP is highly unspecific with respect to the amino acid residue N-terminal to the cleavage point. TPAP is capable of cleavage even following Pro residues and CM-Cys residues. However, a Pro residue C-terminal to the cleavage point completely inhibits cleavage by TPAP. Specific cleavage products obtained from subjecting native proteins to TPAP treatment include the tripeptide sequences IPE, yVD, WRQ, KGA, LPS, ANL, NGT, LMQ, YFE, GPG, GGG, ADG, RST, SVE, KKP, EGV, NTG, AGD, RHN, LKT, VEK, KPE, GVN, TGA, GDR, HNL, HSQ, GTF, TSD, YSK, YLD, SRR, AQD, FVQ, WLM and ATL. EXAMPLE 8 INHIBITION OF A. niger TPAP ACTIVITY Inhibition of TPAP by the protease inhibitor, cloromethylketone Ala-Ala-Phe-CMK (AAF-CMK), was tested under the conditions described above. AAF-CMK was found to inhibit TPAP completely. Addition of AAF-CMK to fermentation broths can totally inhibit the TPAP activity. The thermostability of 5 different AMG batches were investigated with and without the TPAP activity present. The thermostability of all 5 AMG batches were unchanged after 2 weeks storage at 37 °C when TPAP had been inhibited. The corresponding samples without inhibitor were all clearly destabilized. EXAMPLE 9 Portions of 10 ml culture broths obtained from a cultivation of an AMG producing A. niger strain were adjusted to either pH 6.5 or pH 7.0 with sodium hydroxide. The samples were incubated at 25'C, 40°C and 50°C, respectively, for one hour and subsequently the samples were adjusted to pH 4.3 with acetic acid. The storage stability of the treated samples was measured. It was shown that this simple recovery process {based on a pH treatment at elevated temperatures) resulted in efficient removal of TPAP activity (Table 6). Treatment of the culture broth at pH 6.5/40'C for one hour reduced the TPAP activity to 5% and gave a very stable product with an unchanged thermostability after two weeks of storage at 40°C. All numbers in the table are %. The values indicated for TPAP and AMG, respectively, are the relative activity at the time indicated. EXAMPLE 10 PCR CLONINQ From the K-terminal amino acid sequence of A. niger TPAP the sequence of which is shown in SEQ ID Wo. 4 four PCR primers were designed (Table 7} Genomic DMA from a strain of A. niger was used as template in four PCR reactions. PCR fragments in the expected size 65 bp was purified and cloned into the plasTtiid pCR™II (Invitrogen Corporation) . Sequencing of the insert for three clones showed that two of them contains the degenerate sequence in the areas corresponding to the primers, while the sequence in between was invariant to the N-terminal amino acid sequence. In order to clone a larger DNA fragment encoding the tripepti-dyl aminopeptidase the primer #6010 (GCACTGTCTGAAGCAGCTGTACAAC-ATCGGTG) corresponding to the invariant sequence was made. From two other peptide sequences three PCR primers were designed (Table 7). Three PCR reactions (#6010/#59S8, #6010/#5989, and #60l0/#5990 were performed using genomic A. niger DNA as template. The reactions were done at two annealing temperatures -iior- =„^ Ac^an Roarri-inriR *6niQ/#5989 (one fragment or approx. 80 bp) and #6010/#5990 (three fragments of approx. 120 bp, 500 bp, and 950 bp) show the same band pattern on an agarose gel at the two different temperatures. In reaction #6010/#5988 a fragment of approx 120 bp was seen at 42"C, but at 45°C a fragment of approx. 950 bp was seen. The 950 bp fragment turned out to be the right one and was inserted into the pCR II AT vector. An E, coli strain harbouring the 950 kb fragment was deposited with the Deutsche Sammlung von Microorganismen und ZelIkulturen GmbH, Mascheroder Weg lb, D-38124 Braunschweig, Germany on December 5, 1994 as DSM 9570, under the provisions of the Budapest Treaty. The 950 bp fragment was sequenced from both ends. It was found that this fragment encodes the N-terminal part of TPAP. The partial sequence of the N-terminal part is shown in SEQ ID No. 2, the partial sequence obtained from sequencing from the other end is shown in SEQ ID No. 3. The sequence of the entire "950 base fragment" which was found to be constituted by 908 bp, is shown in SEQ ID No. 1. Southern analysis Genomic DNA from a strain of A.niger and from A. oryzae IFO 4177 was isolated as described previously fVelton et al., 1984, Proc. Natl. Acad. Sci. USA. 81: 1470-1474). Genomic DNA was digested with appropriate restriction enzymes, fractionated on a 0.7% agarose gel, and blotted to ImmobilonTM as described by the manofacturer. The membranes were probed for the presence of the 950 bp TPAP gene sequence labelled with alpha-32 dATP (NewEngland) by random priming according to the method described by Feinberg et al., 1983, Anal. Biochem. 132:6. The membranes were then incubated for 2 hours at 65'C in hybridiza¬tion solution (5xSSC (0.15 M NaCl, 0.015 M trisodium citrate), lOxDenhardt (0.2% Ficoll, 0.2% polyvinyl pyrrolidone, 0.2% bovine serum albumin) , 10 mM EDTA, 1% SDS, l50/ig/ml Poly A, 50 Mg/ml yeast RNA). Next, the radioactively labelled probe was added and incubated at 65°C overnight with gentle agitation. The memebranes were washed twice at 30°C for 15 minutes in 2XSSC, 1% SDS. Finally, the membranes were dried, covered with plastic wrap, and exposed to x-ray film (Fuli-RX) at ~70°c. the results show that both strains contain only one gene encoding the TPAP. SEQUENCE LISTING SEQ ID No. I 90S bases. CACTGTCTGAAGCAGCTGTACAACATCGGTGACTACCAGGCCGATCCCAAGTCCGGCAG-CAAGATCGGCTTTGCCAGCTACCTTGAGGAATACGCCCGGTATGCCGATCTCGAGAGG-TTCGAGCAGCACCTGGC TCCCAATGCCATCGGCCAGAACTTCAGCGTCGTCCAATTCAACG-GCGGCCTCAACGATCAGCTTTCA TCGAGTGACAGCGGCGAAGCCAACCTCGACCTGCAGTA-CATCCTGGGCGTCAGCGCTCCCGTCCCCA TCACCGAGTACAGCACCGGCGGACGCGGCGAA-CTAGTCCCCGACCTGAGCTCCCCCGACCCCAACGA CAACAGCAACGAGCCCTACCTTGACT-TCCTTCAGGGAATCCTCAAGCTTAACAACTCCGACCTCCCA CAAGTCATCTCTACCTCCTA-CGGTGAAGACGAACAGGTATGCACCTCACCTGACCCATTCCATTTTA CATCCCTCACCTCT-CTCAACCAAACTAACAACACCAACAGACTATCCCCGTCCCCTACGCCCGCACC GTCTGCAA-CCTCTACGCCCAACTCGGCAGCCGCGGCGTCTCTGTAATCTTCTCCAGCGGCGACTCCG GCGTCGGCGCCGCCTGCCTCACCAACGACGGCACCAACCGCACGCACTTCCCTCCTCAATT CCCCGC CTCCTGCCCCTGGGTAACCTCCGTCGGCGCAACCTCCAAGACCTCCCCCGAGCAA-GCCGTCTCCTTC TCCTCCGGCGGCTTCTCCGACCTCTGGCCCCGCCCCTCCTACCAACACG-CCGCCGTGCAAACCTACC TCACCAAGCACCTGGGCAACAAGTTCTCGGGGCTTTTCAACGC-CTCCGGCCGCGCCTTCCCCGACGTCTCCGCGCAGGGCGTCAACTACGCTGTTTACGACAAA SEQ ID No. 2 CACTGTCTGAAGCAGCTGTACAACATCGGTGACTACCAGGCCGATCCCAAGTCCGGCAGCA AGATCGGCTTGGGCAGCTACCTTGAGGAATACGCCCGGTATGCCGATCTCGAGAGG TTCGAGCAGCACCTGGCTCCAATGCATCGGCAGAACTCAGCGTCGTCCAATTCACGGCGGCT-CACGATCAGCTTCATCGAGTGACAGCGGCGAGCAACTCGACTGCAGTAC SEQ ID NO. 3 CCTCCTACCAACACGCCGCCGTGCAACCTACCTGACCAAGCACCTGGCAACAAGTTCTCGG-GGCTTTTCAACGCCTCCGGCCGCGCCTTCCCCGACGTCTCCGCGCAGGGCGTCAACTACGCT-GTTTACGACAA SEQ ID No. 4 Ala-Gln-Asn-Thr-Ser-His-Cys-Asp-Ser-Ile-Ile-Thr-Pro-His-Cys-Leu-Lys-Gln-Leu-Tyr-Asn-Ile-Gly-Asp-Tyr-Gln-Ala-Asp-Pro-Lys Thr-Ser-Pro-Glu-Gln-Ala-Val-Ser-Phe-Ser-Ser-Gly-Gly-Phe-Ser-Asp-Leu-Trp-Pro-Arg-Pro-Ser-Tyr-Gln-His- SEQ ID NO, 6 Phe-Ser-Gly-Leu-Phe-Asn-Ala-Ser-Gly-Arg-Ala-Phe-Pro-Asp-Val- Ser-Ala-Gln-Gly-Val-Asn-Tyr-Ala-Val-Tyr-Asp-Lys SEQ ID No. 7 Ile-Gly-Phe-Ala-Ser-Tyr-Leu-Gln-Glu-Tyr-Ala-Arg-Tyr-Ala-Asx-Leu-Glu-Arg-Phe-Glu-Gln-His-Leu- SEQ ID No. 8 Xaa-Leu-Asx-Leu-Gln-Tyr-Ile-Leu-Gly-Val-Ser-Ala-Pro-Val-Pro-Ile-Thr-Glu-Tyr-Ser-Thr-Gly-Gly-Arg-Gly-Glu-Leu-Val-Pro- SEQ ID No. 9 Gly-Ala-Leu-Asx-Asp-Ile-Val-Asn-Gly-Thr-Ser-Val-Gly-Gln-Asp-Gly-Arg-Asn-Arg-Phe-Gly-Gly-Thr-Pro-Asn-Gly-Ser- SEQ ID NO. 10 Glu-Leu-Tyr-Asn-Ile-Gly-Asp-Tyr-Gln-Ala-Asp-Ala-Asn-Ser-Gly- Ser-Lys SEQ ID NO. 11 Thr-Thr-Pro-Glu-Arg-Gly-Thr-Tyr-Phe-Ser-Ser-Gly-Gly-Phe-Ser-Asn-Tyr-Trp-Pro-Arg-Pro-Glu-Trp-Gln-Asn-Gln-Ala-Val-Ala-Ser-Tyr-Leu- SEQ ID NO. 12 Gly-Thr-Leu-Gly-Glu-Phe-Asp-Gly-Thr-Ser-Ala-Ser-Ala-Pro-Ala-Phe-Ser-Ala-Val-Ile-Ala-Leu-Leu-Asn-Asp-Ala-Arg-Leu-Arg-Ala-Gly-Lys-Pro-Thr-Leu-Gly-Phe-Leu-Asn-Pro-Trp-Leu-Tyr-Lys SEQ ID NO. 13 Thr-Gly-Arg-Gln-Gly-Leu-Gln-Asn-Ile-Thr-Leu-Gly-Ala-Ser-Ile-Gly-Xaa-Thr-Gly-Arg-Ala-Arg-Phe-Gly-Gly-Ala-Pro-Asn-Gly-Gly-Pro-Val-Val-Pro-Tyr-Ala-Ser- SEQ ID NO X4 Ala-Lys-Xaa-Ile-Ser-His-Yaa-Asp-Ser-Ile-Ile-Thr-Pro-Pro-Yaa- Leu-Lys-Glu-Leu-Tyr-Asn-Ile-Gly- SEQ ID NO 15 Ala-Xaa(1)-Asn-Xaa(2)-Ser-His-Cys-Asp-Ser-Ile-Ile-Thr-Pra-Xaa (3} -Cys-Leu-Lys-Xaa (4) -Leu-Tyr-Asn-IIe-Gly-Asp-Tyr-Gln-Aia-Asp- Xaa(5)-Xaa(6) WE CLAIM: 1. A method of reducing or eliminating the tripeptidyl aminopeptidase (TPAP) production from a TPAP producing cell of the genus Aspergillus, in which method a DNA sequence encoding TPAP or a part thereof essential for exhibiting TPAP activity or the TPAP promoter sequence required for the expression of TPAP from a TPAP encoding DNA sequence present in said cell are modified or inactivated so as to result in a reduced or no TPAP production from said cell. 2. The method as claimed in claim 1, in which the modification or inactivation of the DNA sequence is obtained by subjecting the TPAP producing cell to mutagenesis and selecting for cells for which the TPAP producing capability has been reduced or removed. 3. The method-as claimed in claim 2, in which the mutagenesis is performed by random or site-directed mutagenesis. 4. A method of reducing or eliminating the TPAP production from a TPAP producing cell of the genus Aspergillus, in which method a nucleotide sequence complementary to the TPAP encoding sequence and thus capable of hybridizing to TPAP mRNA produced in the cell is introduced into the cell in such a manner that the nucleotide sequence may be transcribed in the cell vinder conditions allowing the nucleotide sequence to hybridize to the TPAP mRNA and thus reduce the amount of TPAP translated from said mRNA or eliminate any such translation. 5. A microbial host cell prepared according to claims 1 to 4. 6. A method of preparing a product wherein at least 60% of the TPAP activity is removed, which method comprises transforming a host cell as claimed in claim 5 with a DNA sequence encoding the product, culturing the transformed cell under suitable conditions for expression of the product, and recovering the product from the culture. -47- 7. A method of preparing a product wherein at least 60% of the TPAP activity is removed, which product is encoded by a DNA sequence present in a TPAP expressing cell, which method comprises modifying or inactivation a DNA sequence present in said cell and encoding TPAP or a part thereof essendal for exhibiting TPAP activity or the TPAP promoter required for the expression of TPAP from a TPAP encoding DNA sequence as claimed in the method of any of claims 1 -4 and subsequently culturing the cell under suitable condidons for expression of the product, and recovering the product from the culture. 8. A method of preparing a product wherein at least 60% of the TPAP activity is removed by fermentation of a TPAP-producing cell of the genus Aspergillus which also produces the product, which method comprises adding an effecdve amount of Ala-Ala-Phe-chloromethylketone to the fermentation broth either during or after the fermentation has been completed, recovering the product of interest from the fermentation broth, and optionally subjecting the recovered product to further purification. 9. A method of preparing a product wherein at least 60% of the TPAP activity is removed by fermentation of a TPAP-producing cell of the genus Aspergillus which also produces the product, which method comprises subjecting the fermentation broth or an enzyme preparation isolated there from containing TPAP and the product of interest to a combined pH and temperature treatment for a sufficient period of time to reduce the TPAP activity, and optionally recovering the product from the treated broth. 10. The method according to claim 9, in which the TPAP reducing treatment is performed at a pH in the range of 6.5-7 and at a temperature in the range of 25-40° C. 11. The method according to any of claims 6-10, in which the product is an enzyme. 12. The method according to claim 11, in which the product is selected from an amylolytic enzyme, a lipolytic enzyme, a proteolytic enzyme, a cellulytic enzyme, an oxidoreductase, and a plant cell-wall degrading enzyme. -48- 13. The method according to claim 12, in which the product is AMG, lipase, cutinase, cellulase, amylase, protease, peroxidase, transglutaminase, laccase, catalase, glucose oxidase, or phytase. |
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1477-mas-1995 correspondence others.pdf
1477-mas-1995 correspondence po.pdf
1477-mas-1995 description (complete).pdf
| Patent Number | 229251 | |||||||||||||||
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| Indian Patent Application Number | 1477/MAS/1995 | |||||||||||||||
| PG Journal Number | 12/2009 | |||||||||||||||
| Publication Date | 20-Mar-2009 | |||||||||||||||
| Grant Date | 16-Feb-2009 | |||||||||||||||
| Date of Filing | 15-Nov-1995 | |||||||||||||||
| Name of Patentee | NOVOZYMES A/S | |||||||||||||||
| Applicant Address | KROGSHOEJVEJ 36, DK-2880 BAGSVAERD, | |||||||||||||||
Inventors:
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| PCT International Classification Number | C12N09/48 | |||||||||||||||
| PCT International Application Number | N/A | |||||||||||||||
| PCT International Filing date | ||||||||||||||||
PCT Conventions:
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