ENZYMATICALLY-ACTIVE RECOMBINANT HUMAN beta -TRYPTASE AND METHOD OF MAKING SAME

Abstract: Disclosed is a method of expressing enzymatically-active, recombinant human beta -tryptase in a yeast host cell, expression constructs which drive the production of enzymatically-active tryptase in transformed yeast, and genetically-engineered yeast containing the expression constructs and which express enzymatically-active human beta -tryptase. Uses for the tryptase so produced are also disclosed.

Description: ENZYMATICALLY-ACTIVE RECOMBINANT HUMAN 0-TRYPTASE AND METHOD OF MAKING SAME Mark A. Maffitt Andrew L. Niles Mary Haak-Frendscho FIELD OF THE INVENTION The invention is directed to a method of making enzymatically-active human /3-tryptase in a genetically-engineered microbial host, expression constructs encoding human /3-tryptase , and genetically-engineered eukaryotes which express enzymatically- active recombinant human /3-tryptase. DESCRIPTION OF THE PRIOR ART Human mast cell /3-tryptase is a neutral serine protease of presently unknown biological function in vivo. However, it has been implicated in angiogenesis and tissue remodeling. It constitutes up to 20% w/v of the total granule protein of mast cells. /3-tryptase is selectively stored in mast cell granules and is released upon mast cell degranulation. Because /3-tryptase is unique to mast cells, it has gained favor as a specific marker of mast cell-mediated pathology. For a complete discussion regarding mast cell heterogeneity, structure, and mediators, see Nilsson and Schwartz (1994). Purified native human /3-tryptase is a tetrameric endoprotease of approximately 134 kDa. Each of the four subunits is approximately 31 to 34 kDa in size. As noted in Schwartz (1995), human tryptase was first purified to apparent homogeneity from dispersed and enriched lung mast cells in 1981. However, further research has shown that there are at least two different types, or groups, of human tryptase. These tryptase isoforms are designated herein as α-tryptase and /3-tryptase. For purpose of brevity, the unadorned term "tryptase" as used hereinbelow shall refer solely to the β isoform. Human tryptase is isolated conventionally from cadaveric lung tissue, as described by Smith et al. (1984). A number of researchers have reported cloning cDNAs which encode human tryptase, see Miller et al. (1990), Vanderslice et al. (1990), and Blom and Hellman (1993), as well as rat mast cell tryptase, see Ide et al. (1995). However, previous attempts at cloning human tryptase using either bacterial or baculovirus expression systems are plagued with a myriad of problems, including protein folding problems that result in a lack of enzymatic activity. These failures are due, at least in part, to the fact that the tryptase enzyme is extensively modified post-translationally to yield the active form of the enzyme. Consequently, the specific activity of a recombinant tryptase produced in a prokaryote would be expected to be low due to the lack of post-translational glycosylation. As a further consequence, previous attempts to produce enzymatically-active recombinant human tryptase have proven to be far less than ideal because the methods require post-expression chemical modifications to activate the enzyme precursor. For instance, Sakai et al. (1996) report the expression and purification of recombinant human α-tryptase and /3-tryptase precursors in a baculovirus system. However, the tryptase precursors formed are inactive. Regarding the use of methylotrophic yeasts (e.g. , Hansenula polymorpha, Kluyveromyces lactis, Pichia pastori , Schizosaccharomyces pombe, Schwanniomyces occidentalis and Yarrowia lipolyticά) as hosts for the production of heterologous proteins, the characteristics of these organisms and their suitability for such use has been extensively reviewed in the relevant literature. See, for example, Faber et al. (1995) and Buckholz and Gleeson (1991). SUMMARY OF THE INVENTION According to the present invention, DNA encoding human tryptase is cloned, incorporated into a eukaryotic expression vector, and transformed into a suitable eukaryotic host cell. Successfully transformed host cells express, post-translationally process, and secrete enzymatically-active human tryptase. The tryptase so formed has an N-terminal amino acid sequence that is identical to that reported by Vanderslice et al. (1990). Further still, the tryptase produced according to the inventive method has tryptic activity which is comparable to tryptase isolated from cadavers. In particular, the invention is directed to a DNA expression construct comprising, in 5' to 3' order: a promoter, the promoter operationally linked to a signal sequence, and the signal sequence operationally-linked to a DNA sequence encoding human /3-tryptase. In the preferred embodiment, the DNA expression construct comprises, in 5' to 3' order: a promoter selected from the group consisting of GAP, AOX1, MOX, FMD, ADH, LAC4, XPR2, LEU2, GAM1, PGK1, GAL7, GADPH, CYC1, and CUP1, the promoter operationally linked to a signal sequence, the signal sequence operationally-linked to a DNA sequence encoding human /3-tryptase, and the DNA sequence operationally linked to a terminator sequence. Suitable hosts transformed to contain these expression constructs express and secrete enzymatically-active human tryptase. The invention also is directed to a method of producing enzymatically-active human /3-tryptase. The method comprises transforming a yeast host cell with an expression construct as described herein, whereby the host cell expresses enzymatically-active (mature) human /3-tryptase. The invention also is directed to the glycosylated tryptase produced and secreted by the transformed host. A third embodiment of the invention is directed to a genetically-engineered yeast cell which expresses enzymatically-active human /3-tryptase. In the preferred embodiment, the genetically engineered yeast cell comprises a Pichia pastoris host cell transformed to contain and express an expression construct as described herein. The invention entails operationally linking DNA sequences that encode the mature form of tryptase immediately downstream (i.e. , in the 3' direction) and in- frame to a secretion signal sequence to yield an expression construct. The expression construct, the preferred embodiment of which is a plasmid designated pPIC9- HumTry, then is transformed into a suitable host, preferably a strain of Pichia pastoris. Hosts so transformed express and secrete the tryptase encoded by the expression construct. The tryptase expressed is correctly processed by the host cell and secreted into the cell medium as enzymatically-active human tryptase. Another embodiment of the invention is directed to the enzymatically-active, glycosylated, recombinant protein having tryptase activity which is produced by organisms transformed to contain and express the expression construct. The invention is further drawn to a method of generating polyclonal or monoclonal anti-human tryptase antibodies comprising inoculating an animal with the enzymatically-active tryptase produced by organisms transformed to contain and express the expression construct. The invention is also drawn to polyclonal or monoclonal anti-human tryptase antibodies produced thereby. Another embodiment of the invention is a method of screening a substance, such as a chemical compound or mixture of compounds, for its effect on the enzymatic activity of tryptase enzymes. Here, the method comprises contacting the substance with an enzymatically-active recombinant tryptase produced by an organism transformed to contain and express the construct described herein and then measuring the enzymatic activity of the recombinant tryptase. The invention takes advantage of the fact that native tryptase is synthesized as a proprotein. The modified tryptase amplicon described herein lacks the sequences that encode the N-terminal amino acid prosequence. By cloning this sequence as an in-frame fusion to an N-terminal yeast secretion signal sequence, there is no need to subject the secreted tryptase protein to an activation process. It is secreted as an active enzyme without any further exogenous manipulation required. To accomplish this result, the signal peptide cleavage site is positioned immediately adjacent to the N-terminus of mature tryptase protein. Cleavage of the signal peptide by action of a host cell protease then removes the signal peptide from the tryptase as it is secreted. The net result is secretion of an enzymatically active, mature form of tryptase containing the same amino terminal residues found in mature native tryptase molecules isolated from human tissues. A distinct advantage of the method of producing tryptase described herein is that the tryptase so produced does not require any post-expression or post-purification modifications or manipulations to initiate tryptase activity. The tryptase produced according to the invention has enzymatic activity which compares favorably with cadaveric tryptase. The ready availability of enzymatically-active tryptase afforded by the invention immediately provides previously unattained advantages on several fronts. These include facilitating the large scale screening of combinatorial libraries for specific tryptase inhibitors as potential therapeutics, as well as advancing the understanding of the biological significance of tryptase in mast cell-mediated diseases. The availability of enzymatically-active recombinant tryptase also offers several advantages over tryptase derived from cadavers. For example, tryptase produced according to the present invention is free of any human pathogens that can be associated with material derived from cadaveric sources. The method according to the invention can be used to produce large standardized lots ( > 100 mg) of tryptase having defined specifications. The quantity of tryptase produced in the preferred Pichia transformant is sufficiently large to enable larger-scale tryptase studies than were possible in the past, such as pharmacological studies, combinatorial library screens, and X-ray crystallographic studies. The large quantity of tryptase produced also allows for the development of tryptase agonists and/or antogonists. Expression in Pichia also provides a means by which the relationships between tryptase structure and function can be elucidated. Such studies generally utilize a first host wherein the tryptase-encoding DNA is mutagenized and then a second host wherein the peptide encoded by the mutated DNA is expressed. For example, site- directed mutagenesis of tryptase-encoding DNA can be done in conventional E. coli hosts, and the mutated DNA then transferred to a suitable eukaryotic host for expression of the novel tryptase. These and other aims, objects, and advantages of the invention will become apparent upon a complete reading of the following Detailed Description of the Invention and attached claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of pPIC9. Fig. 2 is a graph depicting the secretion of tryptase from GS115 and KM71 cells transformed to contain pPIC9-HumTry. Fig. 3A depicts an electrophoresis gel of culture supernatant from cells transformed to contain pPIC9-HumTry sampled during an induction time course study to evaluate the production of recombinant tryptase after addition of an inducer. Fig. 3B depicts a Western blot of the electrophoresis gel depicted in Fig. 3A. The gel was visualized by probing with biotinylated anti-human tryptase AA5 monoclonal antibody (Promega Corporation). Fig. 4 depicts an electrophoresis gel of culture supernatant from cells transformed to contain pPIC9-HumTry, blotted onto nitrocellulose, blocked with BSA, and probed with a biotinylated anti-human tryptase monoclonal antibody, AA5 (Promega Corporation), to indicate the presence of tryptase. Biotinylated or prestained molecular weight markers were used as protein size references. Fig. 5 is a graph depicting heparin stabilization of the recombinant trytase produced according to the present invention. Fig. 6 is a Western blot depicting recombinant human tryptase according to the present invention and cadaveric human lung tryptase before and after digestion with Endoglycosidase H (Endo H, New England Biolabs, Beverly, Massachusetts, USA) and probed with biotinylated AA5 anti-human tryptase monoclonal antibody. Fig. 7 is a Western blot depicting recombinant human tryptase according to the present invention and cadaveric human lung tryptase before and after digestion with Peptide N-glycosidase F (PNGase F, New England Biolabs). DETAILED DESCRIPTION OF THE INVENTION Definitions: To provide a clear and consistent understanding of the specification and claims, the following definitions are used herein. Terms not expressly described have their standard meaning as understood by those skilled in the art. Enzymatically active - As applied to the expression of heterologous proteins from a genetically-engineered host cell, a protein is enzymatically active when it does not require post-expression or post-isolation chemical processing such as artificial cleavage of a leader peptide or artificial glycosylation in order for the expressed/isolated protein to have the desired activity. Used synonymously with "mature multimeric /3-tryptase. " Expression construct - A DNA construct containing at least one sub-sequence encoding a protein or peptide of interest which is operationally linked to one or more regulatory sub-sequences which drive expression of the encoded protein or peptide when the construct is transformed into a suitable host cell. Such constructs also may contain sub-sequences encoding means for selecting host cells transformed to contain the construct, such as sub-sequences which confer antibiotic resistance or dietary limitations to transformed cells. Host cells - In general, any eukaryote cell amenable to transformation, including, but not limited to, organisms of the genera Hansenula, Kluyveromyces, Pichia, Saccharomyces, Schizosaccharomyces, Schwanniomyces, Yarrowia, and the like, including Hansenula polymorpha, Kluyveromyces lactis, Pichia pastoris, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Schwanniomyces occidentalis and Yarrowia lipolytica. It is preferred that the host be of the genus Pichia and most preferred that the host cell be a Pichia pastoris having the characteristics of ATCC 20864. Leader peptide - An N-terminal extension of generally from 10 to 85 predominately hydrophobic amino acid residues. The leader peptide initiates a secretory pathway resulting in mobilization of the mature protein out of the cytoplasmic compartment. The leader peptide is cleaved from the mature protein chain post-translation and forms no part of the mature protein. "Leader peptide" is synonymous with the term "signal peptide. " Leader sequence - A DNA sequence located between the transcription start site of an operon and the first structural gene. "Leader sequence" is synonymous with the term "signal sequence. " The leader encodes a short peptide called the "leader peptide. " Operationally linked - When referring to joined DNA sequences, denotes that the sequences are in the same reading frame and that upstream regulatory sequences will perform as such in relation to downstream structural sequences. DNA sequences which are operationally linked are not necessarily physically linked directly to one another but may be separated by intervening nucleotides which do not interfere with the operational relationship of the linked sequences. Pichia pastoris - Any strain of the species Pichia pastori , including, but not limited to, those strains having the characteristics of the deposited strains bearing American Type Culture Collection (ATCC, 12301 Parklawn Drive, Rockville, Maryland 20852, USA) Accession Numbers 2604, 20864 (synonymous with strain GS115), 28485, 60372, 66390-66395, 76273, and 76274, as well as Pichia pastoris strain KM71, available commercially from Invitrogen Corporation (San Diego, California, USA). ATCC 20864 (strain GS115) and strain KM71 are the preferred host cell types. Polymerase Chain Reaction (PCR) - A technique in which cycles of denaturation, annealing with a primer pair, and extension with DNA polymerase are used to generate a large number of copies of a desired polynucleotide sequence. See U.S. Patent Nos. 4,683,195 and 4,683,202 for a description of the reaction. Promoter - The DNA sequence site where RNA polymerase binds to the beginning of an operon. A promoter is a DNA sequence that directs the specific transcription of downstream (i.e. , 3') DNA sequences into corresponding RNA sequences. A promoter functions as the start signal for RNA synthesis. The promoter itself is not transcribed. Terminator - A DNA sequence situated at the 3' end of a transcribed sequence that signals the end of transcription. Tryptase: Unless expressly identified otherwise, human mast cell / 3-tryptase. Genetic Engineering: Many of the steps noted below for the manipulation of DNA, including digesting with restriction endonucleases, amplifying by PCR, hybridizing, ligating, separating and isolating by gel electrophoresis, transforming cells with heterologous DNA, selecting successful transformants, and the like, are well known and widely practiced by those skilled in the art and are not extensively elaborated upon herein. Unless otherwise noted, the DNA protocols utilized herein are described in Sambrook, Fritsch, and Maniatis (1989). Isolation of Tryptase-Encoding DNA: DNA sequences encoding human tryptase are isolated by first collecting mast cell samples (4 x 10 6 , 1.1 % of total cells) from a human donor. Poly(A) + RNA is then isolated by LiCl precipitation and oligo(dT)-cellulose chromatography. A cDNA library is constructed in a suitable phage vector (λ ZAP II vector, Stratagene, LaJolla, California, USA) and amplified once in E. coli XLl-Blue cells prior to screening. The library is screened at 42 °C with a dog tryptase cDNA labeled to 2 x 10 8 cpm/μg by nick-translation, in conventional fashion except for using 30% formamide in the hybridization solution. Positive recombinants are identified by autoradiography, plaque -purified, and re-probed. Phagemids containing inserts that hybridize to the cDNA probe are excised from the phage vector using R408 helper phage, transformed into E. coli XLl-Blue cells, and purified by alkaline lysis. The sequence of the cDNA inserts can be determined by dideoxy chain termination modified for double-stranded DNA by using "SEQUENASE" -brand sequencing kit (United States Biochemical, Cleveland, Ohio, USA). The Ml 3 forward, reverse, and KS primers (Stratagene) are used for the initial sequence reaction. Subsequent sequencing reactions use oligonucleotide primers designed from the previously determined sequence. Positive clones can also be used to screen commercial libraries, such as the human placental genomic library in EMBL-3 (Clontech, Palo Alto, California, USA). Here, the cDNA is labeled with biotin-7-dATP by nick-translation and hybridized at 50°C to the immobilized phage DNA and visualized. Positive clones are plaque- purified and re-screened. Phage DNA is purified by the plate lysate method in conventional fashion and digested with BamJAl to yield genomic fragments. The genomic fragments are separated by agarose gel electrophoresis, transferred to nitrocellulose, and hybridized to tryptase cDNA. Hybridizing fragments are ligated into the BamϊJJ site of pBluescript KS + phagemid (Stratagene), and the nucleotide sequence determined as described for the cDNAs. See Vanderslice et al. (1990). A DNA sequence of a tryptase-encoding fragment isolated as described above is depicted in SEQ. ID. NO: 1. Incorporation of Tryptase DNA Into Expression Construct: The DNA encoding the tryptase is then operationally linked with suitable regulatory sub-sequences to drive expression of the tryptase-coding sequence in a eukaryotic host, to yield an expression construct. Preferably, the construct also contains one or more sub-sequences to enable the easy identification of postive transformants. At a minimum, the expression construct should include, operationally linked in 5' to 3' order, a promoter sequence, a signal sequence, the tryptase coding sequence, and a terminator sequence. In this fashion, the promoter will initiate transcription of the downstream signal sequence and tryptase structural gene when incorporated into a suitable host. Several plasmids containing the required regulatory sub-sequences, as well as sub-sequences encoding selectable antibiotic and/or auxotrophic markers and multiple cloning sites are available commercially. A preferred plasmid, pPIC9, is available from Invitrogen (San Diego, California, USA). A schematic of pPIC9 is provided in Fig. 1. pPIC9 is a circular DNA plasmid of 8023 base pairs and contains a 5' AOX1 promoter fragment at bases 1-948, an α-Factor secretion signal (designated S in Fig. 1) at bases 949-1218, a multiple cloning site at bases 1192-1241, and a 3' AOX1 terminator fragment (designated 3' AOX1 (TT)) at bases 1253-1586. pPIC9 also contains an ampicillin resistance gene at bases 7713-6853 and a ColEl origin at bases 6708-6034. The multiple cloning site includes recognition sites for Xhol, SnaBI, EcoRI, Avrll, and Notl. The plasmid also contains Bglll, Sad, Sail, and Stul recognition sites. Other eukaryotic promoter and terminator sequences can be used with comparable success in the expression construct. Generally, the promoter should be homologous to the chosen host in order to ensure efficient expression of the encoded tryptase, although this is not required. The promoter may be constituitive or inducible. Suitable eukaryotic promoter and terminator sequences include (in addition to AOX1) GAP, MOX, FMD, ADH, LAC4, XPR2, LEU2, GAM1, PGK1, GAL7, GADPH, CYC1, CUP1, and the like. This list is illustrative, not exclusive. The DNA sequence encoding the tryptase is introduced into the multiple cloning site of pPIC9 by modifying the 5' and 3' ends of the isolated tryptase DNA sequence to yield complementary overhangs with the sticky ends afforded by the restriction sites contained in the multiple cloning site of pPIC9. The pPIC9 plasmid and the amplified tryptase fragments are then digested with suitable restriction enzymes, hybridized, ligated (T4 DNA ligase), transformed (calcium chloride) into a suitable bacterial host (E. coli strain JM109, Promega Corporation, Madison, Wisconsin, USA is preferred), and positive clones selected by ampicillin resistance, all in conventional and well-known fashion. To modify the ends of the tryptase-encoding DNA fragment, the tryptase DNA is amplified using partially homologous nucleotide primers which include suitable restriction nuclease recognition sites but which do not alter the amino acid sequence of the encoded protein. The resulting amplicon thus encodes the same protein, but includes the restriction sites needed to incorporate the tryptase-encoding fragement into an expression construct. Using knowledge of the tryptase DNA sequence and the degeneracy of the DNA code, any number of suitable primers which will introduce an appropriate recognition site without altering the amino acid sequence of the encoded peptide can be constructed. As described more fully in the Examples, amplifying the DNA sequence as shown in SEQ. ID. NO: 4 with the illustrative primer depicted in SEQ. ID. NO: 2 yields an amplified tryptase-encoding DNA fragment which includes an Xhol restriction site near the 5' end of the fragment and a Notl restriction site near the 3' end of the fragment. These two restriction sites are exemplary only. Virtually any restriction site can be introduced at the terminal ends of the tryptase-encoding DNA fragment without altering the sequence of the encoded tryptase enzyme. The choice is up to the user, and depends almost entirely upon the nature, location, and number of the restriction sites available in the other sub-sequences which are to be incorporated into the ultimate expression construct. The modified amplicon containing the terminal Xhol and Notl sites can then be easily inserted into any plasmid or construct containing an Xhol recognition site and a Notl recognition site, in conventional and well-known fashion. Other sub-sequences may also be included in the expression construct. One particularly helpful sub-sequence is a signal sequence encoding a signal peptide to direct the secretion of the expressed protein from the cell. The signal peptide forms no part of the mature protein - the signal peptide is cleaved from the protein as it passes through the cell wall, thereby yielding the mature protein. For purposes of the present invention, the preferred signal sequence is one that encodes a KEX2 cleavage site in the unprocessed protein. The action of KEX2, a yeast signal peptidase, then will cleave the signal peptide from the remainder of the protein, thereby yielding the mature tryptase enzyme. An α-Factor secretion signal sub-sequence is preferred for secretion of the recombinant tryptase using a Pichia host. After transforming the tryptase-encoding construct into a bacterial host for cloning, positive transformants are screened for the properly assembled expression construct by restriction analysis of plasmids isolated from ampicillin-resistant colonies. The expression constructs are then isolated in standard fashion and transformed into a suitable eukaryotic host for expression of the human tryptase encoded thereon. Transformation of Eukaryotic Host: The expression construct encoding human tryptase then is incorporated into a suitable eukaryotic host. The preferred host is a yeast cell. A eukaryotic host must be used so that the expressed tryptase is properly processed by the cell after translation. Post-translational intracellular processing by the eukaryotic host is critical to impart enzymatic activity to the mature protein. As noted above, the expression constructs can be incorporated into any suitable eukaryotic host, yeast being preferred. The preferred hosts include Hansenula polymorpha, Kluyveromyces lactis, Pichia pastoris, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Schwanniomyces occidentalis and Yarrowia lipolytica. It is most preferred that the host be of the genus Pichia. From among Pichia, it is most preferred that the host cell be a Pichia pastoris cell having the characteristics of ATCC 20864 (strain GS115) or KM71. Transformation is preferably accomplished by electroporation in conventional fashion. The host cells are made electrocompetent by extensive washing with 1 M Sorbitol and then mixed with aliquots of the expression construct which have been pre-digested with a suitable single-cutting restriction enzyme (e.g. , in pPIC9, Sail or Sad) and transformed. Successfully transformed auxotrophs are screened on minimal media, and then rescreened on fresh media to identify clones which produce high levels of tryptase. If operationally linked to an inducible promoter, successfully transformed auxotrophs are screened in a medium containing the required inducer to initiate tryptase production. Tryptase can be assayed from the culture broth using an enzyme-linked immunosorbent assay as described in Niles and Haak-Frendscho, U.S. Patent 5,594, 116, issued January 14, 1997 and assigned to Promega Corporation, and which is incorporated herein by reference. Briefly, suitable microtiter plates are coated with capture antibodies specific for human tryptase derived from immunized avians, preferably chickens. This is done by coating the microtiter plates with a solution of the capture antibody and incubating for 8 to 48 hours at 4°C. The coated plates are then thoroughly rinsed with a solution of tris-buffered saline with "TWEEN" 20 (TBST). Non-specific residual binding to the microtiter plate itself is then blocked by coating the plate with a blocking buffer. A commonly used blocking buffer is a solution of 0.05 % "TWEEN" 20 containing bovine serum albumin (BSA). The plates are again rinsed with TBST. The solutions to be tested are then diluted in the blocking buffer. Preparing a number of serial dilutions is recommended. The plates are then coated with the test solutions and incubated for at least two hours at room temperature. After incubation the plates are again rinsed with TBST. Other buffered solutions, such as phosphate-buffered saline or phosphate-buffered saline with "TWEEN, " also may be used. The next step is to introduce a tryptase detect antibody solution which will bind to the captured tryptase. The preferred detect antibody is a murine-derived monoclonal antibody specific to tryptase. A solution of the monoclonal antibody is prepared and the wells are coated and incubated for at least two hours at room temperature. After incubation, the plates are again washed with TBST. The plates are rinsed with TBST, and are then coated with a conjugate specific antibody /horseradish peroxidase conjugate. Such antibody /horseradish peroxidase conjugates are well known in the art. A conventional method to prepare such conjugates includes using sodium periodate to oxidize the carbohydrate side chains of horseradish peroxidase, followed by the formation of a Schiff base between the activated peroxidase and amino groups of the antibody. The preferred antibody for the conjugate is goat anti-mouse IgG antibodies. The Schiff base then is reduced (sodium borohydride) to yield a stable antibody/enzyme conjugate. The wells of the microtiter plates then are incubated for at least two hours at room temperature. It is important here that the conjugate antibodies must not react with the capture antibody or the tryptase itself. It is preferred that the plates be rinsed with TBS three times prior to addition of the substrate. A horseradish peroxidase substrate solution is then added to each well and the wells incubated for 15 min at room temperature. Acid is added to stop the color reaction. The wells then are examined spectrophotometrically at 450 nm. For colorimetric detection, horseradish peroxidase-conjugated anti-mouse antibody used in conjunction with the substrate 3,3',5,5'-tetramethylbenzidine (TMB) is preferred. Other peroxidase substrates, such as o-phenylenediamine dihydrochloride (OPD) and anti-mouse alkaline phosphatase conjugates function with equal success. This colorimetric double antibody-sandwich ELISA has a sensitivity of about 20 pg/ml, a linear response range from 15 to 2000 pg/ml, and an r > 0.99. End Uses for Enzymatically- Active Recombinant Human Tryptase: A distinct advantage of the recombinant human tryptase described herein is that it is enzymatically active. Because the recombinant tryptase is active, it can be used in any application which would otherwise require using a cadaveric tryptase. For instance, because the recombinant tryptase of the invention has the same biological activity as cadaveric tryptase, it can be used as an antigen to generate anti- human tryptase antibodies in various animals. This is done in well known and conventional fashion by inoculating a test animal, such as a mouse, rat, rabbit, guinea pig, chicken, goat, or other animal, with an initial inoculation of the recombinant tryptase, followed by a series of booster injections. The injections initiate an immunogenic reaction in the animal, resulting in the production of polyclonal antibodies to the recombinant tryptase. To isolate the antibodies, the IgG fraction of the blood serum (or from egg yolks in the case of avians) is isolated in standard fashion. With egg yolks, this can be accomplished utilizing a commercial product such as Promega Corporation's "EGGstract" TM IgY Purification System (Promega Corporation, Madison, Wis. U.S.A.). There also are a number of other methods for isolating immunoglobulins from serum or egg yolks, such as other sequential precipitation methods, which are well known to those skilled in the field. See, for instance, Scopes, R. K. , (1994), "Protein Purification, Principles and Practice, " Springer- Verlag: New York. The conventional method of protein isolation, which is completely satisfactory to isolate anti-human tryptase antibodies, is to "salt out" the protein fractions by precipitation of the proteins from a salt solution. The IgY polyclonal antibodies from the serum of the test animal can be isolated using, for instance, chromatographical methods. Again, there are a number of methods well known to those skilled in the art for isolating immunoglobulins from serum or egg yolk samples. In the same fashion, the recombinant tryptase described herein can be used to generate monoclonal anti-human tryptase antibodies using conventional hybridoma technology. In this technology, a mouse or other test animal is immunized with the recombinant human tryptase to initiate the required immunogenic response. For murine-derived monoclonal antibodies, pristane-primed mice are widely utilized. Spleen cells from the immunized animals are then immortalized by fusion with an immortal cell line, such as a myeloma cell line. The hybrid cells are then serially- diluted, cultured, and screened for those cells which secrete antibodies specific for the recombinant tryptase. The monoclonal antibodies so formed can be used in any number of applications, such as assaying to detect human tryptase, epitope mapping of human tryptase, or for inhibiting tryptase activity for therapeutic or other applications. The tryptase of the present invention can also be used in drug screening for compounds which act as tryptase inhibitors, antagonists, agonists, etc. For example, like most proteins, the recombinant tryptase can be immobilized on a host of supports, such as the plastic of a microtiter plate. So, to screen for tryptase inhibitors, the recombinant tryptase of the present invention can be coated onto a plastic plate, non-specific binding blocked by washing the plate with bovine serum albumin (BSA), and the plate contacted with a putative tryptase inhibitor. The effectiveness of the inhibitor is then determined by measuring the loss of tryptase enzymatic activity as compared to a standard curve of tryptase activity. Likewise, the same approach can be used to screen promising drug candidates for their effects on the enzymatic activity of tryptase. This can be done with the recombinant tryptase immobilized on a suitable solid support, as noted above, or in solution phase. Because the subject recombinant tryptase is enzymatically active, the effect of any given compound on the tryptase can be easily determined by measuring the effect the compound has on the enzymatic activity of the tryptase. The recombinant tryptase can also be used to assay for the presence of tryptase in biological or other solutions. For example, the recombinant tryptase can be used to develop enzyme-linked immunosorbent assays ELISA's for human tryptase. See, for example, U.S. Patent No. 5,744,319 to Niles and Haak-Frendscho for a description of a double antibody-sandwich ELISA. ELISA's come in many different, but related formats, all of which are exceedingly well known to those skilled in the field. A format widely used due to its relative ease of use and wide linear response range is known as the double antibody-sandwich ELISA. The basic protocol for a double antibody-sandwich ELISA is as follows: A plate is coated with antibodies (called capture antibodies) specific for the immunoglobulin being assayed. In this case, the capture antibodies are polyclonal or monoclonal antibodies specific for the recombinant tryptase which are isolated as described above. The plate then is washed with a blocking agent, such as bovine serum albumin (BSA) to block non-specific binding of immunoglobulins to the test plate. The solution to be tested for the presence of tryptase then is incubated on the plate coated with the capture antibodies. The plate then is washed, incubated with detect antibodies, washed again, and incubated with a specific antibody-enzyme conjugate. After incubation, the unbound conjugate is washed from the plate and enzyme substrate is added. The presence of the bound antibody-enzyme conjugate results in a proportional color change which can be measured and quantified. For detecting very low levels of tryptase, levels which might be below the detection limit of a given assay, the recombinant tryptase can be used in known quantities (or activities) to spike samples, thereby increasing the concentration of tryptase in the samples being assayed above the detection limit and into the linear response range of the assay being used. Because the present invention enables the production of large amounts of enzymatically active recombinant tryptase which can be extensively characterized and subjected to quality control measures, antibodies against the recombinant tryptase can be raised and utilized in any number of assay formats to detect the presence of tryptase and to measure the effect of different compounds on the enzymatic activity of tryptase. EXAMPLES The following Examples are included solely to provide a more complete understanding of the subject invention. The Examples do not limit the scope of the invention described and claimed herein in any fashion. Example 1: Construction of pPIC9-HumTry: The 5' and 3' ends of the human tryptase gene encoded by pBSHumTry (see Vanderslice et al. , 1990) were modified via PCR using a pair of partially homologous oligonucleotide primers, SEQ. ID NO: 2 and SEQ. ID NO: 3. The modified tryptase fragment was ligated to the Xho I and Not I sites of pPIC9 (Invitrogen) downstream of the α-Factor secretion signal found on pPIC9 (see "S" in Fig. 1) to yield an expression construct designated pPIC9-HumTry. E. coli strain JM109 (Promega Corporation, Madison, Wisconsin, USA) was transformed with the ligation mix using standard protocols (calcium chloride). Transformants were screened for properly constructed pPIC9-HumTry constructs by restriction analysis of the plasmid DNA isolated from ampicillin-resistant colonies. Example 2: Transformation of Pichia pastoris with pPIC9-HumTry: Fresh cultures of Pichia pastoris strains GS115 (ATCC 20864) and KM71 (Invitrogen) were prepared for electroporation by extensive washing with 1M Sorbitol. Electrocompetent cells were mixed with aliquots of pPIC9-HumTry DNA produced according to Example 1 that had been digested with one of either Sail, Bglll, or Sad, and transformed. Transformants were initially identified as His + prototrophs on minimal media. Methanol utilization phenotypes were analyzed via replica plating on both minimal dextrose and minimal methanol grid plates. Table 1: Media Composition: Filter sterilize. Example 3: Screening for Tryptase Expression: Those clones from Example 2 that secreted detectable levels of tryptase were further screened in order to identify those that secreted high levels of tryptase. Cells were grown overnight at 30°C in 96-well plates in a suitable media. In this Example, the media used was BMGY (buffered minimal glycerol complex media) (commercially available from Invitrogen), the composition of which is listed above in Table 1. Overnight cultures were transferred to fresh media using a 96-pin inoculating device, then incubated overnight at 30°C. Following a third culture step, the growth of each set of 96 cultures was nearly synchronous. Induction of the synchronized cultures was conducted in 96-well plates containing 200 μl BMMY (buffered minimal methanol complex media) (Invitrogen) per well for 3 days at 30 °C. Culture supernatants were sampled each day in order to monitor tryptase accumulation, and to reduce culture volumes for the addition of more methanol. Those clones that excelled at tryptase secretion in 96-well plates were re-screened following induction of the 5 ml cultures. The cumulative results of the screening are depicted in Fig. 2. To generate the data presented in Fig. 2, individual transformants were plated on minimal methanol grid plates. Mature colonies were transferred from the grid plates to nitrocellulose filters and screened for secreted tryptase using a modified Western blot protocol (Wung et al. 1996). Filters were sequentially incubated with anti-tryptase IgY (chicken) and goat anti-chicken alkaline phosphatase conjugate. Blots were developed using a NBT/BCIP substrate ("WESTERN BLUE"-brand, Promega Corporation) according to standard protocols. Colonies associated with purple spots were scored as immunoreactive, all others were scored as negative. Out of the 257 colonies screened in this Example, 197 secreted immunologically detectable levels of tryptase. The fraction of GS115 transformants that secreted tryptase (81 %) was slightly larger than for KM71 (71 %). However, neither strain exhibited a clear advantage over the other in terms of the yield of productive clones generated from a single transformation. There was also no clear correlation between productive clone yield and integration site (i.e. , Bgl II, Sac I, or Sal I). A GS115 clone that arose from integration of pPIC9-HumTry at the Sail site (i.e. , a His+ insertion), was identified as one which secreted high levels of tryptase. This clone, designated GS115/HumTry 5-37, was used for all of the following Examples. The GS115/HumTry 5-37 clone has been deposited with the American Type Culture Collection, 10801 University Boulevard, Manassas, Virginia, USA, under accession no. ATCC 74468, in accordance with the terms of the Budapest Treaty. Example 4: Fermentation of GS115/HumTry 5-37: A glycerol stock of the GS115/HumTry 5-37 clone was fermented under standard conditions. Induction was performed under generic conditions known to be suitable for a wide variety of proteins. Supernatants were sampled after 0, 18.5, 26.5. 43.5, 51.5, 67.5, and 73.5 hours of induction. Samples of the fermentation were analyzed by SDS-PAGE, Western blot, and by activity assay. Fig. 3 A depicts an electrophoresis gel produced during the induction time course study. To produce this gel, 5 μL samples of each fermentation time point (labelled in hours post-induction in Fig. 3) were loaded onto a 4-20% Tris-glycine reducing gel. Following electrophoresis, the gel was stained with "SYPRO ORANGE "-brand stain (Molecular Probes, Eugene, Oregon, USA) and visualized using a "VISTA FLUORIMAGER" (Molecular Dynamics, Sunnyvalle, California, USA). Cadaveric tryptase was included as a control. As shown in Fig. 3 A, prior to induction, only modest levels of tryptase were detectable either by Western blot or enzymatic activity in the fermentation supernatants. Following induction, there was a dramatic increase in both tryptase concentration and tryptase activity. Tryptase accumulation was enhanced by supplementing the BMMY media with 0.5 mg/ml heparin (See Example 5 and Fig. 5). This resulted in nearly linear accumulation of both tryptase and tryptase activity. Prestained molecular weight markers were used as protein size references and mature cadaveric tryptase was used a positive reference control. Fig 3B depicts a Western blot of the gel depicted in Fig. 3 A. The gel was blotted onto nitrocellulose, blocked with BSA, and probed with a biotinylated anti- human tryptase monoclonal antibody, AA5 (Promega Corporation), to indicate the presence of tryptase. The blots were then incubated with streptavidin-alkaline phosphatase conjugate and developed with nitroblue tetrazolium/5-bromo-4-chloro-3- indolyl phosphate, in conventional fashion. This Western blot clearly shows the increased production of tryptase following induction. Another gel of culture supernate post-induction, run in parallel with biotinylated molecular weight markers, is depicted in Fig. 4. This Western blot was produced and visualized in the same fashion as Fig. 3B. Example 5: Heparin Stabilization of Secreted Tryptase: A single GS115/HumTry 5-37 colony was transferred to 200 ml BMGY and grown overnight at 30 °C in shake flasks. Overnight cultures were concentrated by centrifugation and resuspended at an Agoo of 0.5 in either BMMY or BMMY + 0.5 mg/ml heparin. Shake flask inductions were performed at 30°C for 3 days. Activity assays were performed at 24, 48, and 72 hours postinduction using the N-α-benzoyl- DL-arginine- -nitroanalide (BAPNA) cleavage assay. The results are presented in Fig. 5. As shown in Fig. 5, the presence of heparin during induction stabilized tryptase, thereby resulting in increased enzymatic activity. To generate the data in Fig. 5, supernatants with or without heparin were sampled at 24, 48, and 72 hours post- induction and assayed for activity using BAPNA. Activity of the secreted tryptase was measured by incubating the culture supernatants in 1 mM Tris-HCl (pH 8.0), 1 M glycerol, and 1 mM BAPNA at 37°C. Rates of change in absorbance at 410 nm were monitored for each sample. Relative reaction rates were expressed as the slope of the line plotting the change in absorbance over time (i. e. , ΔA 410 /Δt), thereby demonstrating the benefit of exogenous heparin. Example 6: Glycosidase Treatment: Aliquots of recombinant human tryptase and cadaveric human lung tryptase were digested with either Endoglycosidase H (Endo H, New England Biolabs, Beverly, Massachusetts, USA) or Peptide N-glycosidase F (PNGase F, New England Biolabs). Each glycosidase treatment contained 10 μg tryptase. Aliquots of each reaction were removed immediately prior to addition of the glycosidase to serve as undigested controls. Detection was by Western blot with anti-human tryptase monoclonal antibody AA5 (Promega). The results indicate that the recombinant protein produced according to the invention is glycosylated (see Figs. 6 and 7) and the specific activity compares favorable to materials isolated from cadavers. In Figs. 6 and 7, the glycosylation of the recombinant human tryptase (rHT) of the subject invention is compared to the glycosylation of cadaveric human lung tryptase (HLT). The lanes marked "U" in Figs. 6 and 7 are lanes containing recombinant or cadaveric human lung tryptase which were not treated with a glycosidase. The lanes marked "T" contain the corresponding recombinant or cadaveric tryptase after treatement with PNGase F (Fig 6) or Endo H (Fig. 7). The lanes marked "No Tryptase" are negative controls which do not contain tryptase but do contain glycosidases and all buffers. Protein molecular weight markers are included in the outermost lanes of Fig. 6 and the right-hand lane of Fig. 7. Figs. 6 and 7 indicate the presence of three major immunoreactive isoforms of tryptase with apparent molecular weights of 29, 32, and 34 kD. A fourth (apparently minor) isoform migrates as a diffuse smear at about 45 kD. The heterogeneity of the tryptase isoform mixture is reduced to a "core protein" of 29kD by digestion with either PNGase F or Endo H. (See the columns marked "rHT + " in Figs. 6 and 7.) Tryptase isolated from natural sources contains at least 4 electrophoretically distinguishable isoforms having apparent molecular weights that range from 29 to 32kD. In the same fashion as the recombinant tryptase, the heterogeneity of the cadaveric tryptase is reduced to a "core protein" of 29kD following PNGase F digestion (Fig. 6). However, in contrast to the recombinant material, the isoforms present in the cadaveric tryptase are resistant to digestion by Endo H. Example 7: Purification from Culture Media: In this Example, the yield and activity of tryptase from a 112 mL sample of media from a fermentation of GS115/HumTry 5-37 is presented. This Example demonstrates the ease of purification and high recovery of tryptase using the subject invention: Table 2: Purification Data from 112ml conditioned media preparation Specific activity was determined by TBE assay. Example 8: Comparision of Kinetics: In this Example, the kinetics of the recombinant human tryptase according to the present invention (rHT) were compared to the kinetics of cadaveric human lung tryptase (HLT). The results are shown in Table 3: Table 3: Kinetic Data - rHT v. HLT: Example 9: Comparison of Activity: In this Example, the activity of the recombinant human tryptase according to the present invention (rHT) was compared to the kinetics of cadaveric human lung tryptase (HLT) available commercially from Bioprocessing, Inc ("BPI," Scarborough, Maine, USA). Activity was assayed using the BAPNA assay as described above. The results are shown in Table 4: Table 4: Activity: rHT v. Commercially-Available HLT Tryptase: Buffer = Tris/glycerol (pH 7.8) Substrate = BAPNA Samples were diluted 1:50 and 1 : 100 in buffer It is understood that the recombinant human tryptase and the methods to obtain the recombinant human tryptase are not confined to the particular reagents, host organisms, and genetic manipulations expressly illustrated and described herein, but embrace all modified and equivalent forms thereof as come within the scope of the attached claims. BIBLIOGRAPHY Blom, T. and Hellman, L. (1993), Scand. J. Immunol.37:203-208. Buckholz, R.G. and Gleeson, M.A.G. (1991), Biotechnology.9:1067-1072. Faber K.N.; Harder, W.; Ab, G.; and Veenhuis, M. (1995), Yeast.11:1331- 1344. Ide, H.; Itoh, H.; Tomita, M.; Murakumo, Y.; Kobayashi, T.; Maruyama, H.; Osada, Y.; and Nawa, Y. (1995), J. Biochem.118:210-215. Miller, J.S.; Moxley, G.; and Schwartz, L.B. (1990), J. Clin. Invest.86:864- 870. Nilsson and Schwartz (1994) "Mast-Cell Heterogeneity: Structure and Mediators," Blackwell Scientific Publications, Boston, pp.195-208. Sakai K.; Long, S.D.; Dove-Pettit, D.A.; Cabral, G.A.; and Schwartz, L.B. (1996), Protein Express. & Purif.7:67-73. Sambrook, J.; Fritsch, E. F.; and Maniatis, T. (1989), Molecular Cloning: A Laboratory Manual; Cold Spring Harbor Laboratory Press: New York, NY. Schwartz (1995), "Structure and Function of Human Mast Cell Tryptase," Biological and Molecular Aspects of Mast Cell and Basophil Differentiation and Function, chapter 14:161-173, Raven Press, Ltd: New York. Smith, T.J.; Hougland, M.W.; and Johnson, D.A. (1984), J. Biol. Chem. 259(17): 11045-11051. Vanderslice P.; Ballinger, S.M.; Tam, E.K.; Goldstein, S.M.; Craik, C.S.; and Caughey, G. H. (1990), Biochemistry.87:3811-3815. Wung, J.L. and Gascoigne, R.J. (1996), BioTechniques .21:808-812.

Claims: CLAIMS What is claimed is: 1. A DNA expression construct characterized by, in 5' to 3' order: a promoter, the promoter operationally linked to a signal sequence, the signal sequence operationally-linked to a DNA sequence encoding human /3-tryptase, and wherein the expression construct drives the expression of enzymatically-active human / 3-tryptase in hosts transformed to contain the expression construct. 2. The DNA expression construct according to Claim 1, wherein the DNA sequence encoding human /3-tryptase encodes human lung tryptase. 3. The DNA expression construct according to Claim 1 or Claim 2, wherein the DNA sequence encoding human /3-tryptase encodes an amino acid sequence as shown in SEQ. ID. NO: 6 4. The DNA expression construct according to any one of Claims 1, 2, or 3, wherein the DNA sequence encoding human /3-tryptase is SEQ. ID. NO: 1 5. The DNA expression construct according to any one of the preceding claims, wherein the signal sequence encodes a KEX2 cleavage site. 6. The DNA expression construct according to any one of the preceding claims, wherein the signal sequence includes a 3' terminus encoding amino acid residues Leu-Glu-Lys-Arg. 7. The DNA expression construct according to any one of the preceding claims, wherein the promoter is a constituitive promoter. 8. The DNA expression construct according to any one of the preceding claims, wherein the promoter is an inducible promoter. 9. A DNA expression construct characterized by, in 5' to 3' order: a promoter selected from the group consisting of AOX1, GAP, MOX, FMD, ADH, LAC4, XPR2, LEU2, GAMl, PGKI, GAL7, GADPH, CYCI, and CUPl, the promoter operationally linked to a signal sequence, the signal sequence operationally- linked to a DNA sequence encoding human /3-tryptase, the DNA sequence operationally linked to a terminator sequence. 10. The DNA expression construct according to Claim 9, wherein the DNA sequence encoding human (3-tryptase encodes human lung tryptase. 11. The DNA expression construct according to Claim 9 or Claim 10, wherein the DNA sequence encoding human /3-tryptase encodes an amino acid sequence as shown in SEQ. ID. NO: 6 12. The DNA expression construct according to any one of Claims 9, 10, or 11, wherein the DNA sequence encoding human (3-tryptase is SEQ. ID. NO: 1 13. The DNA expression construct according to any one of Claims 9 through 12, wherein the signal sequence encodes a KEX2 cleavage site. 14. A method of producing enzymatically-active human /3-tryptase characterized by transforming a yeast host cell with an expression construct according to any one of the preceding claims, wherein the host cell expresses enzymatically- active human (3-tryptase. 15. The method according to Claim 14, wherein a host cell of the genus Pichia is transformed. 16. The method according to Claim 14, wherein a Pichia pastoris host cell is transformed. 17. The method according to Claim 14, wherein a host cell having the characteristics of Pichia pastoris ATCC 20864 or Pichia pastoris strain KM71 is transformed. 18. The method according to any one of Claims 14 through 17, further comprising isolating the enzymatically-active human /3-tryptase produced. 19. A method of producing enzymatically-active human /3-tryptase comprising transforming a yeast host cell with an expression construct according to Claim 9, wherein the host cell expresses enzymatically-active human /3-tryptase. 20. A genetically-engineered yeast cell which expresses enzymatically-active human /3-tryptase comprising a Pichia pastoris host cell transformed to contain and express an expression construct according to any one of Claims 1 through 13. 21. A genetically-engineered yeast cell according to Claim 20, having the characteristics of ATCC 74468. 22. An enzymatically-active, glycosylated, recombinant protein having tryptase activity produced according to the method recited in any one of Claims 14 through 19. 23. A method of generating polyclonal or monoclonal anti-human tryptase antibodies comprising inoculating an animal with an enzymatically-active protein produced according to Claim 22. 24. Polyclonal or monoclonal anti-human tryptase antibodies produced according to the method of Claim 23. 25. A method of screening a substance for its effect on enzymatic activity of tryptase enzymes comprising contacting the substance with an enzymatically-active protein according to Claim 22 and then measuring the enzymatic activity of the enzymatically-active protein.

Inventors: HAAK-FRENDSCHO MARY, MAFFITT MARK A, NILES ANDREW L, HAAK-FRENDSCHO, MARY, MAFFITT, MARK, A., NILES, ANDREW, L.
Applicants: PROMEGA CORP, PROMEGA CORPORATION
Application year: 1998
Main classification: C12N15
IPC codes: C07K16, C12N1, C12N9, C12N15, C12P21, C12Q1, C12R1