METHOD OF REMOVING N-TERMINAL ALANINE RESIDUES FROM POLYPEPTIDES WITH AEROMONAS AMINOPEPTIDASE

Abstract: This invention describes a method of removing N-terminal alanine residues from polypeptides, preferably recombinant proteins, using an aminopeptidase derived from the marine bacterium Aeromonas proteolytica. Accordingly, Aeromonas aminopeptidase (AAP; E.C. 3.4.11.10) can be used to remove N-terminal alanyl residues from derivatives of human somatotropin (hST, human growth hormone, or hGH), porcine somatotropin (pST), and bovine somtotropin (bST), for example, to yield proteins having their native amino acid sequences. The enzyme reactions can be carried out in free solution, or the AAP can be immobilized on a solid support, for reactions carried out in vitro. An efficient method for converting Ala-hGH to hGH, for example, comprises expression of Ala-hGH in E. coli, recovery of inclusion bodies, solubilization and refolding in detergent, detergent removal by ultrafiltration, selective precipitation, enzyme cleavage, followed by two column chromatography steps.

Description: Method of removing N-terminal alanine residues from polypeptides with Aeromonas aminopeptidase Priority The present application claims priority under Title 35, United States Code, § 119 of United States Provisional Application Serial No. 60/132,062, filed April 30, 1999. Field of the invention This invention describes a method of removing N-terminal alanine residues from polypeptides, preferably recombinant proteins, using an aminopeptidase derived from the marine bacterium Aeromonas proteolytica. Accordingly, Aeromonas aminopeptidase (AAP; E.C. 3.4.11.10) can be used to remove N- terminal alanyl residues from derivatives of human somatotropin (hST, human growth hormone, or hGH), porcine somatotropin (pST), and bovine somatotropin (bST), for example, to yield proteins having their native amino acid sequences. The enzyme reactions can be carried out in free solution, or the AAP can be immobilized on a solid support, for reactions carried out in vitro. An efficient method for converting Ala-hGH to hGH, for example, comprises expression of Ala- hGH in E. coli, recovery of inclusion bodies, solubilization and refolding in detergent, detergent removal by ultrafUtration, selective precipitation, enzyme cleavage, followed by two column chromatography steps. Background of the invention Recombinant proteins that mimic or have the same structure as native proteins are highly desired for use in therapeutic applications, as components in vaccines and diagnostic test kits, and as reagents for structure/function studies. Mammalian, bacterial, and insect cells are commonly used to express recombinant proteins for such applications. Bacterial expression systems, however, are often used when large quantities of protein are needed for experimental or clinical studies, and the protein is capable of being refolded to its proper conformation. Bacterial systems, in particular, offer significant cost advantages over other expression vector systems when eukaryotic post-translational modifications (e.g., glycosylation) are not required, or desired, in the final protein product. Recombmant proteins expressed in bacteria such as E coli, are often sequestered into insoluble inclusion bodies Heterologous protems harvested from inclusion bodies often retam an additional ammo acid residue such as methionme at their ammo terminus This methionme residue (encoded by the ATG start codon) is often not present, however, on native or recombinant proteins harvested from eukarvotic host cells The ammo termini of many protems made m the cytoplasm of E coli, however, are processed by enzymes, such as methionme aminopeptidase (Ben Bassat et al , J Bactenol 169: 751-757, 1987), so that upon expression the methionme is ordinarily cleaved off the N-termmus The ammo acid composition of protein termini are biased in many different manners (Berezovsky et al , Protein Engineering 12(1) 23-30, 1999) Systematic examination of N-exopeptidase activities led to the discovery of the 'N-termmal'- or 'N-end rule' the N-termmal (f)Met is cleaved if the next ammo acid is Ala, Cys, Gly, Pro, Ser, Thr, or Val If this next ammo acid is Arg, Asp, Asn, Glu, Gin, He, Leu, Lys or Met, the initial (f)Met remains as the first ammo acid of the mature protein The radii of hydration of the ammo acid side chains was proposed as phvsical baει« for these observations (Bachmam et al Science 234 179-186 1986 V arshavsky, Cell, 69 725-735, 1992) The half-life of a protein (from 3 mm to 20 hours), is dramatically influenced by the chemical structure of the N-termmal ammo acid (Stewart et al , J Biol Chem , 270 25-28, 1995, Gπegoryev et al , J Biol , Chem , 271 28521-28532, 1996) Site-directed mutagenesis was subsequently used to confirm the 'N-end rule' by monitoring the life-span of recombinant proteins containing altered N-termmal ammo acid sequences (Varshavsky, Proc Natl Acad Sci USA, 93 12142-12149, 1996) A statistical analysis of the amino acid sequences at the amino termini of proteins suggested that Met and Ala residues are over-represented at the first position, whereas at positions +2 and +5, Thr is preferred (Berezovsky et al , Protein Engineering 12(1) 23-30, 1999) C terminal biases, however, show a preference for charged ammo acids and Cys residues (Berezovsky et al , Protein Engineering, 12(1) 23-30, 1999) Recombinant proteins that retain the N-termmal methionme, in some cases, have biological characteristics that differ from the native species lacking the N-terminal methionme Human growth hormone that retains its N-termmal methionme (Met-hHG), for example, can promote the induction of undesireable antibodies, compared to hGH purified from natural sources or recombinant hGH that is prepared m such a way that has the same primary sequence as native hGH (lacking an N-terminal methionme) Low-cost methods of generatmg recombinant protems that mimic the structure oi native proteins are often highly desired for therapeutic applications (Sandman et al , Bio / Technology 13 504-6 (1995)) One method of preparing native proteins m bacteria is to express the desired protein as part of a larger fusion protein containing a recognition site for an endoprotease that specifically cleaves upstream from the start of the native ammo acid sequences The recognition and cleavage sites can be those recognized by native signal peptidases, which specifically clip the signal peptide of the N- terminal end of a protein targeted for delivery to a membrane or for secretion from the cell In other cases, recognition and cleavage sites can be engineered into the gene encoding a fusion protem so that recombinant protein is susceptible to other non-native endoproteases in vitro or in vivo The blood clotting factor Xa, collagenase, and the enzyme enterokinase, for example, can be used to release different fusion tags from a variety of protems Economic considerations, however, generally preclude use of endoproteases on a large scale for pharmaceutical use Another method of preparing native proteins in bacteria is to use the enzvme methionme aminopeptidase (MAP) to proces= the N-terminal methionme from E coh-derived recombinant protems Met-hGH for example, can be treated with MAP to generate hGH United States Patents 4,870,017 and 5,013,662 descnbe the cloning, expression, and use of E coli methionme aminopeptidase to remove Met from a variety of peptides and Met-IL-2 The ability to release ammo acids from a variety of peptide substrates was analyzed, revealing that MAP cleaves only N-termmal methionme on peptides that are at least three amino acids long The nature of ammo acids m the second and third positions also appear to be significant Methionme was released, for example, from Met-Ala-Met, Met-Gly- Met, Met-Ala-Pro-Thr-Ser-Ser-Ser-Thr-Lys-Lys-Thr-Gln-Leu (SEQ ID NO 1), and Met-Pro-Thr-Ser-Ser-Ser-Thr-Lys-Lys-Gln-Cys (SEQ ID NO 2), but not Met-Phe- Gly, Met-Leu-Phe, Met-Met-Met, among others No amino acids were released from Leu-Ala-Pro-Thr-Ser-Ser-Ser-Thr-Lys-Lys-Thr-Gln-Leu (SEQ ID NO 3), Ala- Pro-Thr-Ser-Ser-Ser-Thr-Lys-Lys-Thr-Gln-Leu (SEQ ID NO 4), or Pro-Thr-Ser- Ser-Ser-Thr-Lys-Lys-Gln-Cys (SEQ ID NO 5) WO 84/02351 discloses a process for preparing ripe (native) proteins such as human growth hormone or human promsulm from fusion protems usmg leucme aminopeptidase A fusion protem having the ammo acid sequence (Y m Y 2 Y,)- (Pτo) p -(X,X 2 X.) m which the (Y„ Y 2 Y,)-(Pro) p is the pro-sequence and the rest is the πpe protein, m is an integer greater than 2, Y is an arbitrary ammo acid, p is 0, if X, or X j is Pro, and 1 if X, or X, is different from Pro X is an arbitrary ammo acid, and n is an mteger greater than or equal to 4 is converted by stepwise cleavage with aminopeptidase removing ammo acids Y_. Y 2 if p = 1 or X = Pro, or the groups Y a Y--Y, if X, = Pro and then the two ammo acids Y,-Pro if p=l are cleaved off enzvmatically in one or two steps m a manner known per se. and similarly Y alone is cleaved off, if X, = Pro European Patent Application EP 0 204 527 Al discloses a method of removing the N terminal methionme from protems of the formula H-Met-X-Pro-Y- OH to vield a protem represented by the formula H-X-Pro-Y-OH, where X is an ammo acid other than prohne and Y is a peptide cham Aminopeptidase M was preferred, but leucme aminopeptidase, ammopeptidase PO, or ammopeptidase P could also be used The N-terminal methionme was removed from derivatives of human mterleukm-2 and human growth hormone Aeromonas aminopeptidase (AAP), an exo-peptidase isolated from the marine bacterium Aeromonas proteolytica, can also be used to facilitate the release of N-termmal am o acids from peptides and protems (Wilkes et al., Eur. J Biochem 34(3) 459-66 1973) The most favorable sequence is X-//-Y- whereas Y is a hvdrophobic residue, preferably an aromatic ammo acid such as phenylalanme Residues susceptible to hydrolysis include all hydrophobic, aromatic, and basic ammo acids, plus prohne Aspartyl, glutamyl, and cysteic acid residues were not removed from the ammo terminus of any substrate tested, even at high enzyme concentrations Asparagine, glutamine, and aminoethylated cysteine, however, were released from ohgopeptide substrates Glycine was generally resistant to hydrolysis, but was slowly released from some substrates, depending on the adjacent residues The activity of AAP on peptide substrates can also be enhanced by changing the counter metal ions, such as Cu 2* and Ni 2* for free enzyme AAP (Prescott et al , Biochem Biophys. Res Comm 114(2) 646-652, 1983) AAP is a 29 5 kDa metalloenzyme containing two disulfide bonds European patent EP 0191827 Bl and U S patent 5,763,215 describe the sequential removal of N-terminal amino acids from analogs of eukaryotic proteins, formed m a foreign host, by use of Aeromonas aminopeptidase When 8 mg methionyl-human growth hormone (Met-hGH) (dissolved m 1 mL pH 9 5 10 mM Na borate buffer) was mixed with Aeromonas am opeptidase (dissolved at 0 4725 mg/ L m pH 9 5 Tns buffer) at a ratio of 900 to 19 and mcubated at 37°C, methionme cleavage was complete in 15 mm Cleavage of the new N-termmal ammo acid leucme, was slight after 22 h The N-termmal methionme from Met- pST Met-Interferon, Met-IGF-1, Met-mterleukιn-2 (Met-IL-2), and Met- Apolipoprotein E were removed by AAP. An N-terminal alanine, however, was not removed from mature superoxide dismutase. More complicated methods can also be used to generate recombinant proteins with a native amino terminus. United States Patent 5,783,413, for example, describes the simultaneous or sequential use of (a) one or more aminopeptidases, (b) glutamine cyclotransferase, and (c) pyroglutamine aminopeptidase to treat amino-terminally-extended proteins of the formula NH 2 -A- glutamine-Protein-COOH to produce a desired native protein. The first aminopeptidase(s) (selected from the group consisting of dipeptidylaminopeptidase I, Aeromonas aminopeptidase, aminopeptidase P, and proline aminopeptidase), catalyze the removal of residues amino-terminal to the glutamine. The glutamine cyclotransferase catalyzes the conversion of the glutamine to pyroglutamine, and the pyroglutamine aminopeptidase catalyzes the removal of pyroglutamine to produce the desired protein product. United States Patents 5,565,330 and 5,573,923 disclose methods of removing dipeptideε from the amino-terminuε of precursor polypeptides involving treatment of the precursor with dipetidylaminopeptidase ( dDAP) from the slime mold Dictostelium descoideum, which has a mass of about 225 kDa and a pH optimum of about 3.5. Precursors of human insulin, analogues of human insulin, and human growth hormone containing dipeptide extensions were processed by dDAP when the dDAP was in free solution and when it was immobilized on a suitable solid support surface. More efficient strategies to process amino acids from the amino terminus of recombinant proteins are desirable to reduce the cost of generating therapeutic proteins that mimic the structure of native proteins. Methods that increase the levels of expression or facilitate the downstream processing of recombinant proteins will also accelerate the selection and development of small chemical molecules and other protein-based molecules destined for large scale clinical trials. Summary of the invention It is an object of the invention is to describe a method of removmg an N- terminal alanyl group from a recombinant protem which comprises contactmg said recombinant protem with Aeromonas ammopeptidase such that said N-termmal alanyl group is removed and recovering the resultmg recombinant protem Preferably, the recombinant protem is of eukaryotic origin Even more preferably, the recombinant protem is selected from the group consisting of human growth hormone (hGH), bovine somatotropin (bST), porcme somatotropm (pST), and human tissue factor pathway inhibitor (TFPI) Most preferably, the recombinant protein is hGH Preferably, the contacting process is earned out at a pH from about pH 7 to about pH 11 Even more preferably, the contactmg process is earned out at a pH from about pH 8 to about pH 10 Most preferably, the contacting process is earned out at a pH of about pH 8 0 to about pH 9 5 Preferably, the contactmg process is earned out the presence of a buffer selected from the group consistmg of borate, CHES, sodium bicarbonate, sodium phosphate, and Tns-HCl More preferably, the buffer is borate, phosphate, or Tns- HC1 Preferably, the contacting process can be earned out wherem the ammopeptidase is immobilized Preferably, the ammopeptidase is immobilized on a chromatography resm, chromatography surface, or chromatography gel Preferably, the recombinant protein is passed through a column containing the ammopeptidase immobilized on a chromatography resm Alternatively, the contactmg process can be earned out wherein the ammopeptidase is not immobilized (e g , in free solution) It is also conceivable that Aeromonas ammopeptidase may permit the processing of protems containing two or more closely-spaced alanyl residues in the N-termmal regions of polypeptides The ammopeptidase may proceed sequentially from the N-termmus of the polypeptide or perhaps recognize additional alanine residues withm a short distance of exposed N-termmal polypeptide residues Elucidation of a consensus sequence for the alanyl-specific recognition and cleavage sites can be evaluated on a vanetv of protem and peptide substrates Aeromonas ammopeptidase may also facilitate the processmg of non-alanyl residues m the N-termmal regions of protems under the conditions disclosed in this application Elucidation of a consensus sequence for the recognition and cleavage of these sites can be evaluated on a vanety of protem and peptide substrates It is another object of the invention is to descnbe a method of removmg ammo-termmal amino acids from a precursor polypeptide of the formula X-Y-Pro-Z with Aeromonas aminopeptidase to yield a polypeptide of the formula Y-Pro-Z, wherem X is one or more amino acids except prohne, Y is any ammo acid except prohne, and Z is one or more ammo acids Preferably. X is alanine Preferably, Y is selected from the group consisting of phenylalanine, methionme, threonine, and aspartic acid More preferably, Y is phenylalanine Most preferably, X is alanine and Y is phenvlalanme Preferab the precursor polypeptide is Ala-hGH Deβnitions The following is a list of abbreviations and the corresponding meanings as used interchangeably herein: g = gramis) HPLC = high performance liquid chromatography kb = kilobase(s) mb = megabase(s) mg = milligram(s) ml, mL = milliliter(s) RP-HPLC = reverse phase high performance liquid chromatography ug, μg = microgram(s) ul, uL, μl. μL = microliter(s) The following is a list of definitions of various terms and the corresponding meanings as used interchangeably herein: The terms '"aap " and "AAP' " mean Aeromonas aminopeptidase The terms "ap " and "AP " mean ammopeptidase The term "amino acid(s)" means all naturally occurring L-amino acids, including norleucine, norvaline, homocysteine, and ornithine. The term "fusion molecule" means a protein-encoding molecule or fragment thereof that upon expression, produces a fusion protein. The term "fusion protein" means a protein or fragment thereof that comprises one or more additional peptide regions not derived from that protein. The term "promoter" is used in an expansive sense to refer to the regulatory sequence(s) that control mRNA production. The term "protein fragment" means a peptide or polypeptide molecule whose amino acid sequence comprises a subset of the amino acid sequence of that protein. The term "protein molecule/peptide molecule" means any molecule that comprises five or more amino acids. The term ""recombinant" means any agent (e.g., DNA, peptide, etc.), that is, or results from, however indirectly, human manipulation of a nucleic acid molecule. The term "specifically bind" means that the binding of an antibody or peptide is not competitively inhibited by the presence of non-related molecules. The term "substantially-purified" means that one or more molecules that are or may be present m a naturally-occurnng preparation containing the target molecule will have been removed or reduced in concentration. Brief description of the figures Figure 1 - Structure of Ala-hGH and hGH Human growth hormone (right) is a single-chain polypeptide (22 kDa) with four cysteine residues involved in two disulfide bond linkages. The correct N- terminal sequence can be achieved by the in-vitro enzymatic cleavage of Ala-hGH (left) with Aeromonas aminopeptidase. Figure 2 - Process for Production of hGH from Ala-hGH A general process for the purification of hGH from Ala-hGH involves purification of Ala-hGH from bacterial inclusion bodies, refolding of Ala-hGH in detergent, detergent removal, acid precipitation, treatment with aminopeptidase, and purification of the native hGH by cation and amon exchange column chromatography. Figure 3 - Kinetics of removal of Ala from Ala-hGH by AAP The kinetics of removal of Ala from Ala-hGH by AAP are illustrated in Figure 3. Ala-hGH was present at 3 mg/ml and AAP at was present at 0.5, 1.0, 2.0, 3.0, and 4.0 units/ml in a total volume of 6 ml. The reactions were performed at room temperature and samples collected up through 25 hours and the products analyzed by ES/MS. Most of the reactions for the three highest concentrations of AAP were complete by 6 hours. Figure 4 - Enzymatic cleavage process options - Column mode A schematic comparison of steady-flow and continuous-flow cleavage process modes are illustrated. Figure 5 - Batch mode cleavage of Ala-hGH Figure 5 illustrates a time course of enhanced cleavage of Ala-hGH by Cu- AAP compared to Zn-AAP in batch mode. Figure 6 - Recirculation mode cleavage of Ala-hGH Figure 6 illustrates a time course of Ala-hGH by Cu-AAP compared to Zn-AAP carried out in column recirculation mode. Figure 7 - Cleavage efficiency analyzed by HPLC Figure 7 illustrates HPLC profiles of Ala-hGH before cleavage with AAP, incomplete cleavage, and after the reaction is complete. Figure 8 - Product comparison by RP-HPLC Figure 8 illustrates the HPLC profile of hGH prepared by treating Ala- hGH with AAP, and two commercial preparations of hGH (Humatrope and Zomacton). Figure 9 - Products of Ala-hGH treated with AAP analyzed by tryptic mapping Figures 9-12 illustrate typical tryptic map profiles Figure 9 illustrates the profile tracings illustrating the difference in mobility of the Ala-Tl peptide compared to the Tl peptide. Figure 10 - Quantitative analysis of residual Ala-hGH in hGH by tryptic digest Figure 10 shows a vertically expanded profile tracing, illustrating the differences in peak areas under the elution positions for Ala-Tl and Tl. Figure 11 - Product comparison by tryptic mapping Figure 11 illustrates the tryptic maps of hGH purified after treatment of Ala-hGH with AAP compared to tryptic maps of hGH from commercial sources (Humatrope and Zomacton). Figure 12 - Residual levels of Ala-hGH in the final product by tryptic mapping Figure 12 shows a vertically expanded profile tracing illustrating the presence or absence of Ala-Tl in a crude preparation of hGH, the final bulk preparation of hGH, and hGH from two commercial sources (Humatrope and Zomacton). Figure 13 - Cleavage efficiency analyzed by ES/MS Figure 13 illustrates ES/MS profiles of Ala-hGH before cleavage with AAP, incomplete cleavage, and after the reaction is complete. Figure 8 illustrates the HPLC profile of hGH prepared by treating Ala-hGH with AAP, and two commercial preparations of hGH (Humatrope and Zomacton). Figure 14 - Product analysis by RP-HPLC, SE-HPLC, and ES/MS Figure 14 illustrates a supenmposed ES/MS profile of Ala-hGH and hGH (bottom panel) along with HPLC tracings of the final product resolved on RP-HPLC and SE-HPLC columns. Figure 15 - Product analyzed by N-terminal sequencing Figure 15 illustrates tracmgs of the products released after cycle 1 and cycle 2 from an automated protein sequencer. Phenylalanine (18.3 min) is the only significant residue detected after one cycle (left panel) Proline (14.2 min) is the only significant residue detected in cycle 2 The amount of alanine (*) is negligible in both cycles, indicating lack of N-termmal alanine residues m the final purified product. Detailed description of the invention The following examples will illustrate the invention m greater detail, although it will be understood that the invention is not limited to these specific examples Vanous other examples will be apparent to the person skilled in the art after reading the present disclosure without departing from the spmt and scope of the invention It is intended that all such other examples be included withm the scope of the appended claims General methods General methods of cloning, expressing, and charactenzing protems are found m T Maniatis, et al , Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory, 1982, and references cited therein, incorporated herein by reference, and m J Sambrook, et al., Molecular Cloning, A Laboratory Manual, 2 nd edition, Cold Spring Harbor Laboratory, 1989, and references cited therein, incorporated herein bv reference General and specific conditions and procedures for the construction manipulation and isolation of antιbodιe c are well known the art (see, for example, Harlow and Lane, In Antibodies A Laboratory Manual, Cold Spnng Harbor Press, Cold Spring Harbor, New York (1988)) Reagents Aeromonas ammopeptidase and all specialty chemicals, unless noted otherwise, were obtained from Sigma Chemical Company (St Louis, MO) Humatrope was obtained from Eh Lilly Zomacton was obtained from Gentechnisch Protein Purification Protem punfication can be accomplished usmg any of a vanety of chromatographic methods such as ion exchange, gel filtration, hydrophobic chromatography, or reversed phase HPLC These and other protem punfication methods are descnbed m detail in Methods in Enzvmology, Volume 182 "Guide to Protem Punfication" edited by Murray Deutscher, Academic Press, San Diego, Califorma, 1990 Folded proteins can also be affinity-punfied usmg affinity reagents such as monoclonal antibodies or receptor subunits attached to a suitable matrix Punfied proteins can be analyzed bv RP-HPLC, electrospray mass spectrometry, and SDS-PAGE Protein quantitation is accomplished by ammo acid composition, RP-HPLC and Bradford protem determination techniques Tryptic peptide mapping, performed m conjunction with electrospray mass spectrometry, can also be used to confirm the identity of protems Example 1: Preparation of Alanyl-human growth hormone (Ala-hGH) Ala-hGH (Figure 1) was expressed m E coli usmg mini-Mu-based chromosomal expression system (Wemberg et al , Gene 126 25-33, 1993, U S patents 5,395,763 and 5,514,483, U S patent application 09/044,369, filed March 19, 1998, each herein specifically incorporated by reference) Ala-hGH was expressed at levels of about 1 5 to about 2 0 g/liter Ala-hGH was punfied refolded, and processed to a punty of >90% based on analysis of Ala-hGH (by RP-HPLC) and total protem concentration (by absorbance at A, 80 ) Bnefly, inclusion bodies were isolated and Ala-hGH was punfied and refolded using methods described previously (WO 98/29433) Refolding was most common a detergent The detergent was then removed from the refold mixture by exhaustive ultrafiltration (10 TOVs) against pH 10 water This was followed by an acid precipitation step to remove most of the recombinant E coli protems The average recovery of Ala-hGH from this precipitation step was -80-85% This semi-punfied Ala-hGH was diafiltered against the cleavage buffer (10 mM phosphate, pH 8 0) before being treated with the enzyme, preferably in an immobilized mode After the enzymatic cleavage step, hGH was further punfied by ion exchange chromatography to bulk powder A general process outline is illustrated m Figure 2 Example 2: In-υitro processing of Ala-human growth hormone (Ala-hGH) with Aeromonas aminopeptidase in free solution Pnor to the cleavage step, Ala-hGH was adjusted to 3 mg per ml concentration in 10 mM borate, pH 9 5 To this, Aeromonas ammopeptidase was added m 3 units per ml and the reaction was allowed to proceed for 24-36 hours at ambient temperature or at a shorter time at 37°C The progress of the cleavage reaction can be monitored by RP-HPLC or by ammo acid analysis of the release of alanine from Ala-hGH At the end of reaction, the solution was quenched by adding 2% acetic acid (1 1 5 dilution w /w) The kinetics of removal of Ala from Ala-hGH by AAP are illustrated in Figure 3. Ala-hGH was present at 3 mg/ml and AAP at was present at 0.5, 1.0, 2.0, 3.0, and 4.0 units/ml m a total volume of 6 ml. The reactions were performed at room temperature and samples collected up through 25 hours and the products analyzed by ES/MS. Most of the reactions for the three highest concentrations of AAP were complete by 6 hours. Example 3: In-vitro processing of Ala-human growth hormone (Ala-hGH) using immobilized aminopeptidase Preparation of immobilized aminopeptidase Aeromonas ammopeptidase (AAPj was coupled onto resms such as Sepharose 4B resin via the cyanogen bromide (CNBr) chemistry Commercial CNBr-activated Sepharose 4B resm was washed exhaustively with cold water and then suspended m 0 1 M sodium carbonate buffer. pH 8 5 or 10 mM phosphate, pH 8 AAP was added (100 units per gram of resm) and the mixture was gently agitated at 4°C for overnight After washing with water, the resm was capped with ethanolamine (0 5-1 M) at room temperature for two hours Resm was then washed with water and equilibrated with the enzyme cleavage buffer, such as 10 mM phosphate, pH 8 The activity of this immobilized enzyme was measured by the standard assay, suggested by Sigma, usmg L-leucme-p-nitroamlide as a substrate The average activity was typically 10-20 units per ml of resm bed ]n vitro cleavage of Ala human growth hormone (hGH) Batch mode: Immobilized aminopeptidase was suspended as 1.1 mix in borate or phosphate buffer. To a 7-ml tube containing 5 ml Ala-hGH in phosphate or borate buffer, one ml resm was added. This gave a total of 6 ml with 3 mg/ml protem concentration. The mixture was rocked for 10-24 hours at 20-40°C At the end of reaction, resm was filtered off and the resulting solution was analyzed by RP- HPLC The remaining of the solution was centnfuged using a CentnCon micro- filtration device The filtrate was analyzed by the ammo acid analyzer for the releasmg of alanme The retentate was exchanged 4-5 times with 2% acetic acid before bemg dned down to powder for mass spectrometry analysis Table 1 illustrates the effect of temperature on batch mode cleavage of Ala- hGH usmg immobilized AAP The reaction is accelerated at ambient temperatures, and essentially complete beyond 54 hours Table 1: Effect of temperature on batch mode cleavage of Ala-hGH using immobilized AAP Temperature Time, hrs % cleavage 4-6 c C 16 48 54 65 89 75 Ambient 16 82 54 >97 89 >97 Circulation mode. Ala-hGH in 10 mM borate, pH 9.5 or 10 mM phosphate, pH 8.0 was circulated onto a Sepharose column that was previously immobilized with Aeromonas aminopeptidase. The volume of the reservoir is between 100 ml to 700 ml depending on the concentration of the protem. Typically, Ala-hGH is in 5-10 mg per ml. The flow rate is between 2-4 ml per minute. This was performed at 20°C for about 24 hours. The reaction was monitored by RP-HPLC. Cleavage efficiency was confirmed by mass spectrometry and N-terminal sequencing. Finished product was then further purified by ion exchange chromatography. Table 2 illustrates the effect of flow rate on cleavage of Ala-hGH using immobilized AAP at 28°C in recirculation mode. Shorter residence times, were generally associated with higher levels of uncleaved substrate. Table 2: Circulation mode cleavage of Ala-hGH at 28 °C Flow rate Flow rate Residence time % Non-cleaved * (ml/min) ( l/hr) (hrs) Trypsin digest 0.119 7.14 7.14 0.92 0.167 10.03 5.08 1.18 0.262 15.72 3.24 2.11 0.400 24.00 2.13 (1.65) 0.573 34.38 1.48 2.26 0.867 52.02 0.98 2.17 * The experiment was performed at 28°C in a column volume of 51 ml using 10 mM phosphate, pH 8 as buffer using Ala-hGH: 8 mg/ml (HPLC). Table 3 illustrates the effect of flow rate on cleavage of Ala-hGH using immobilized AAP at 20 C C in recirculation mode. Shorter residence times, directly correlated with higher levels of uncleaved substrate. Table 3: Circulation mode cleavage of Ala-hGH at 20 °C Flow rate Flow rate Residence time % Non-cleaved ' (ml/min) (ml/hr) (hrs) Trypsin digest 0.117 7.02 7.26 1.34 0.164 9.84 5.18 2.12 0.255 15.27 3.34 3.83 0.404 24.21 2.11 4.54 0.567 34.87 1.46 5.20 0.849 50.94 1.00 14.99 1.23 73.64 0.69 21.27 The experiment was performed at 20°C with a column volume of 51 ml. in 10 mM phosphate buffer, pH 8 using Ala-hGH: 8 mg/ml (HPLC). * Approximately 1% are the cysteine adduct that co-eluted with the non-cleaved Ala-Tl peptide. Flow-through mode: Ala-hGH (8 mg/ml concentration) in 10 mM borate, pH 9.5 or 10 mM phosphate, pH 8.0 was introduced onto a Sepharose column (column volume is 50 ml) that was previously immobilized with Aeromonas aminopeptidase. The flow was adjusted to 15 ml per hour so the residence time to be around 3 hours. Cleavage efficiency was confirmed by RP-HPLC, tryptic digest, mass spectrometry or N-terminal sequencing. The eluent was collected and processed for downstream chromatographic purification. Table 4 illustrates the effect of flow rate on cleavage of Ala-hGH using immobilized AAP at 28°C in flow-through mode. Most of the Ala-hGH was processed by AAP under these conditions. Table 4. Flow-through mode cleavage at 28 °C Flow rate (ml/hr) Residence ti e (hrs) % non-cleaved * (based on Trypsin digest) 7.14 7.14 <0.92 10.03 5.08 <1.18 15.72 3.24 <2.11 24 2.13 NA 34.4 1.48 <2.26 52.02 0.98 NA * All the tryptic data are based on the combination of uncleaved Ala-hGH and a process impurity. The real value of the uncleaved Ala-hGH is estimated about 50% of the reported values. Example 4: Comparison of steady-flow and continuous-flow cleavage processes Column mode cleavage can be done at a much lower flow rate in one pass as long as the overall residence time is met Run #1 was a typical run in the recirculating mode Run #2 was operated at 1/10 of the flow rate of run #1 However, run #2 was performed at 175 mm per pass as compared to 18 mm per pass for run #1 The overall residence time for both runs is about the same, -180 minutes The two modes are illustrated in Figure 4 Table 5 Effect of flow rate on activity Run # Column Volume, Flow rate, Total Residence Residence ml ml hr passes time per time total pass contact time 57 192 10 18 min 180 mm 0 i 19 8 1 1 75 mm 175 mm Table 6 illustrates the effect of the number of passes on cleavage of Ala- hGH usmg immobilized AAP at 28°C in recirculation mode. Most of the Ala-hGH was processed by AAP under these conditions. Table £> • Re-circulation at 28 °C in phosphate buffer Time, hrs # passes % cleavage Analyzed by 2 92 1 06 >93 RP-HPLC 5 73 2 08 >96.1 Tryptic map 15.57 5.66 >98.6 Tryptic map 17 73 6.45 >98 6 Tryptic map 20.4 7.42 >98.6 Tryptic map 23 4 8 8 >98.8 Tryptic map 24 4 8 87 >98 8 Tryptic map 39 7 14 44 >99 2 Tryptic map [Ala-hGH] = 9 2 mg/ml, 500 ml load Table 7 illustrates the effect of temperature and residence time on cleavage of Ala-hGH A ten degree difference m temperature appears to affect the cleavage efficiency A longer residence time may be required if a higher % cleavage is needed Table 7 Effect of temperature and residence time on steady-flow cleavage process Run # Temperature, Flow rate, Residence time, % cleavage* °C ml hr min 1A 20 0 28 182 >98 5 IB 30 0.28 182 >99.1 2A 20 0.51 100 >95 8 2B 30 0.51 100 >98 3 * Cleavage products were analyzed by the peptide mappmg method Example 5: Enhancement of AAP alanyl-processing activity with copper The effects of substituting Cu 4 or Ni ' for the native Zn * catalytic cofactor of AAP were examined in the immobilized system for in vitro processing of Ala- hGH. This Cu-AAP can be prepared either directly from the AAP purification process step or be converted to the copper species by replacing the zinc counter metals that is present as in the commercial material. The conversion can be done either as the free enzyme or as the immobilized form. Immobilized Cu-AAP from Zn-AAP Sepharose: Cu-AAP was immobilized as described above. Resin slurry (sample A, 20 ml with 10 ml resin bed volume) was placed in a 250-ml sinter-glass funnel and drawn to near dryness using by vacuum. To this, 20 ml of 50 mM Tricine/50 mM KC1, pH 7.5 and 20 mM 1,10 phenanthroline were added and mixed for 20 minutes. The solution was removed and placed in fresh buffer containing 1,10- phenanthroline and mixed for another 2 hours. The buffer was removed and the resin slurry was washed with water and HEPES buffer. pH 7.5. The resulting resin was divided into two tubes each with a total volume of 12 ml. To B, 0.2 mM CuCL, in 50 mM HEPES, pH 7.5 was added, and to C, 0.2 mM ZnCL, in 50 mM HEPES, pH 7.5 was added. Both tubes were rocked gently for 3 hours. The slurries were washed extensively with water and stored in the desired buffer, such as borate, pH 9.5. Table 8: Activity of metallo-modified AAP against Leu-pNA Samples Metallo AAP Activity unit/ml bed substrate: Leu-pNA A (as is) Zn-AAP 8.94 B Zn-AAP 8.59 C Cu-AAP 5.47 The rate of Ala-hGH cleavage by Cu-AAP and Zn-AAP was compared in both batch and recirculating column modes. In the batch cleavage trial, 0.5 ml of a 1:1 slurry of each resin (B or C) was added to 2.056 ml of 10 mM borate buffer, pH 9.5 prior to the addition of Ala-hGH to a final concentration of 0.8 mg/ml. The reactions were followed over 24 hours bv collection of samples that were quenched by filtering out the immobilized enzvme through a 0 45 um filter The filtrate was then analyzed bv RP-HPLC to determine the fraction of Ala-hGH that had been cleaved In the recirculating column cleavage tnal, 1 cm x 5 cm columns were poured containing either the Cu-AAP resm (B) or the control AAP resm (B) These columns were equilibrated with 10 mM phosphate and 50 ml of 4 75 mg/ml Ala- hGH was recirculated through each of the columns at 2 CV per hour Aliquots were collected and quenched at 3 hr, 6 hr, 18 hr and 28 hr for analysis as above Figure 5 illustrates a time course of enhanced cleavage of Ala-hGH by Cu- AAP compared to Zn-AAP batch mode Figure 6 illustrates a time course of Ala- hGH by Cu-AAP compared to Zn-AAP earned out in column recirculation mode Under all reaction conditions examined, Cu 2* -substιtuted AAP was the most active against Ala-hGH (Figures 5 and 6), even though the Cu-AAP is less active the hydrolvsis of the chromogenic substrates Leu-p-mtroanihde (pNA) (Table 8) Example 6: Detailed structural analysis of the product produced by treatment of Ala-hGH with Aeromonas aminopeptidase Purification of Ala-hGH Dissolution I Re fold The inclusion body (IB) slurry was added to a pre-mixed solution containing 34 5 grams of sodium bicarbonate, 156 grams of ammo-acid (e g , sarcosme and/or glutamic acid) based detergent and 826 ml of water The dissolved IB solution was held for 20 minutes at room temperature and cystine solution (100 mM, pH 10 0) was added The solution was stined for 15 hours at room temperature before cooling down to 4°C The finished refold mixture was then concentrated to 4 liters, before being diafiltered against pH 10 water Acid precipitation The diafiltered solution was diluted with pH 10 0 water to an Ala-hGH concentration of -2 5 mg/ml A 2% acetic acid solution was added usmg a penstaltic pump until the pH reached -5 6 at 4-6°C The acidified solution was stirred for an additional 30 minutes The solution was then centnfuged at 6000 RPM for 30 minutes using a Sorvall RC5C centrifuge at 4°C. The supernatant was decanted and was then diafiltered against 10 mM sodium phosphate, pH 8.0. The protein concentration was then adjusted to 8 mg/ml. Enzymatic cleavage: Aeromonas aminopeptidase was coupled onto resins such as Sepharose 4B resin via the cyanogen bromide chemistry (Hermanson, 1992). The activity of this immobilized enzyme was measured by the standard assay as suggested by Sigma using L-leucine-p-nitroanilide (Leu-pNA) as a substrate. Cold Ala-hGH solution (8 mg/ml) in 10 mM phosphate, pH 8.0 was passed through an immobilized enzyme column that was equipped with a water jacket and maintained at 25°C. The flow rate was adjusted to -8 ml/hr to assure a sufficient contact time between Ala-hGH and the immobilized enzyme. The cleavage pool was then buffer exchanged against 3 M urea, 0.05 M acetic acid, pH 5.0 (buffer A) before loading onto the cation column. Cation column: The cation load was introduced onto a 2.2 x 20 cm Amicon column packed with CM Sepharose resin. The total column load was 2.0 g of Ala-hGH. After loading, the column was washed with 1 CV (column volume) of buffer A, then eluted with a salt gradient from 0-0.2 M NaCl over a total of 54 CVs. The flow rate was 4 CV/hour. Column eluent was collected in 0.2 CN fractions and the eluent was monitored with a Gilson holochrome detector at 280 nm. Fractions were analyzed by cation exchange HPLC, and fractions with >95% purity were pooled. Anion column: The cation pool was loaded onto a 1.6 x 20 cm Amicon column that was packed with Pharmacia Q-Sepharose resin. After loading, column was washed with one CV of Buffer A. A 40 CN linear gradient of 0-0.15 M ΝaCl in 0.05 M Tris- Cl pH 7.5 was done. The column eluent was collected as above. Fractions were analyzed by anion exchange HPLC and fractions with >98% purity were pooled. Structural analysis of the cleavage products The most convenient method for the analysis of a cleavage reaction is the RP-HPLC method. However, the only reliable quantitative analysis is the peptide digest method. In this method, the detection limit for Ala-Tl is 0.25%. Amino acid analysis: After the cleavage reaction, the solution was centrifuged using a Centricon with 10 kDa molecular weight cut-off membrane. The alanme concentration in the filtrate can be measured by an amino acid analyzer. The degree of cleavage can then be calculated by the amount of alanine released from the reaction. In addition, any other amino acid detected should be an indication of non-specific cleavage. RP-HPLC analysis: An isocratic method utilizing N-propanol (NPA)/0.25M phosphate pH 6.5 (26:74) as the mobile phase was used for analyzing Ala-hGH and hGH on a Vydac 214ATP54 column. The separation was carried out at 40°C. This method was used mainly in monitoring the formation of hGH via enzymatic cleavage of Ala-hGH. It also served as a secondary tool in deciding which fractions to collect from a cation exchange column. ■ ■■ _ Figures 7 and 8 illustrate typical HPLC profiles. Figure 7 illustrates HPLC profile ' s, of Ala-hGH before cleavage with AAP, incomplete cleavage, and after the reaction is complete. Figure 8 illustrates the HPLC profile of hGH prepared by treating Ala-hGH with AAP, and two commercial preparations of hGH (Humatrope and Zomacton). Peptide mapping using trypsin: A solution of hGH was adjusted to pH 7.5 with 0.5 N NaOH. This solution was diluted with Tris base (50 mM, pH 7.5) so that the final concentration was 2 mg/ml. Then 15 L of trypsin solution (1 mg/mL in 50 mM Tris base, pH 7.5) was added. The sample was mixed and incubated at 37°C for 4 hrs, then quenched with 50 mL of HC1 (0.5 M). An aliquot of the digested solution was injected on RP- HPLC and peptides were resolved by an acetonitrile gradient with 0.1% TFA. This method provides information for the assessment of the primary and secondary structural integrity of hGH. Most importantly, this is the best method for analyzing trace level of un-cleaved Ala-hGH in the cleavage reaction and in the final product. The only difference between the tryptic digests of hGH and Ala-hGH is the N-terminal octa-peptide, Tl vs. Ala-Tl. These two peptides are baseline resolved using an isocratic RP-HPLC method. Tl : FPTIPLSR ( SEQ ID NO : 6 ) Λia-Tl : AFPTIFLSR ( SEQ ZD NO : Figures 9-12 illustrate typical tryptic map profiles. Figure 9 illustrates the profile tracings illustrating the difference in mobility of the Ala-Tl peptide compared to the Tl peptide. Figure 10 shows a vertically expanded profile tracing, illustrating the differences in peak areas under the elution positions for Ala-Tl and Tl. Figure 11 illustrates the tryptic maps of hGH purified after treatment of Ala- hGH with AAP compared to tryptic maps of hGH from commercial sources (Humatrope and Zomacton). Figure 12 shows a vertically expanded profile tracing illustrating the presence or absence of Ala-Tl in a crude preparation of hGH, the final bulk preparation of hGH, and hGH from two commercial sources (Humatrope and Zomacton). Electrospray mass spectrometry (ES/MS): Measurement is based on the peak intensity for hGH (22,125) and Ala-hGH (22,195). The presence of other peaks is indicative of non-specific enzymatic cleavage. Figure 13 illustrates ES/MS profiles of Ala-hGH before cleavage with AAP, incomplete cleavage, and after the reaction is complete. Figure 8 illustrates the HPLC profile of hGH prepared by treating Ala-hGH with AAP, and two commercial preparations of hGH (Humatrope and Zomacton). Figure 14 illustrates a superimposed ES MS profile of Ala-hGH and hGH (bottom panel) along with HPLC tracings of the final product resolved on RP-HPLC and SE-HPLC columns. N-terminal sequencing: N-terminal protein sequencing was performed by standard methods. The relative amounts of Ala (present in Ala-hGH) and Phe (in hGH) as the N-terminal amino acid are indicative of the degree of cleavage. Internal cleavage can also be detected by N-terminal sequence analysis. Figure 15 illustrates tracings of the products released after cycle 1 and cycle 2 from an automated protein sequencer. Phenylalanine (18.3 min) is the only significant residue detected after one cycle (left panel). Prohne (14.2 min) is the only significant residue detected in cycle 2. The amount of alanine (*) is neghgible in both cycles, indicating lack of N-terminal alanine residues in the final purified product. Example 7: In-vitro processing of Alanyl Tissue Factor Pathway Inhibitor (Ala-TFPI) using amino peptidase: Ala-TFPI, isolated from E coli ( US 5,212,091), can be processed to TFPI usmg AAP in solution. Properly refolded Ala-TFPI is adjusted to 0.5-3 mg per ml concentration m 10 mM phosphate, pH 8.0 or 10 mM borate, pH 9.5 To this, Aeromonas ammopeptidase is added to a concentration of 3 units per ml and the reaction is allowed to proceed for 24-36 hours at ambient temperature or for a shorter time at 37°C. The progress of the cleavage reaction can be monitored by HPLC method or by ammo acid analysis of the release of alanme from Ala-TFPI. At the end of reaction, the solution is quenched by add g 2% acetic acid (1:1.5 dilution w/w) The degree of cleavage is determmed by HPLC analysis of the tryptic peptide fragments and by ES/MS of the isolated product Ala-TFPI can also be processed to TFPI using an immobilized AAP as described above. The degree of cleavage is determined by HPLC analysis of the tryptic peptide fragments and by ES/MS of the isolated product All references, patents, or patent applications cited herein are incorporated by reference in their entirety, as if written herem.

Claims: Claiπis A method of removing an N-termmal alanvl group from a recombmant protem which compnses contactmg said recombinant protem with Aeromonas ammopeptidase such that said N-termmal alanyl group is removed and recovenng the resulting recombinant protem 2 A method of claim 1 wherem said recombinant protem is of eukaryotic ongm 3 A method of claim 2, wherem said recombinant protem is selected from the group consistmg of human growth hormone (HGH), bovine somatotropin (bST), porcme somatotropin (pST), and human tissue factor pathway inhibitor (TFPI) A method of claim 1, wherem said contacting is earned out at a pH from about pH 7 to about pH 1 5 A method of claim 4, wherem said contactmg is earned out at a pH from about pH 8 to about pH 10 6 A method of claim 5, wherem said contactmg is earned out at a pH of about pH 8.0 to about pH 9.5 A method of claim 1, wherem said contactmg is earned out m the presence of a buffer selected from the group consistmg of borate, CHES, sodium bicarbonate, sodium phosphate, and Tns-HCl 8 A method of claim 7, wherem said buffer is borate 9 A method of claim 7 wherem said buffer is sodium phosphate 10 A method of claim 7, wherem said buffer is Tns-HCl A method of claim 1, wherem said ammopeptidase is immobilized 12 A method of claim 11, wherem said ammopeptidase is immobilized on a chromatography resm, chromatography surface, or chromatography gel 13 A methoα of claim 12 wnerein said recombmant protem is passed through a column containing said ammopeptidase immobilized on a chromatography resin 14 A method of claim 1, wherem said aminopeptidase is not immobilized (earned out in free solution; 15 A recombmant protem lacking an N-terminal alan e prepared by the method of claim 1 A method of removing ammo-termmal ammo acids from a precursor polypeptide of the formula X-Y-Pro-Z with Aeromonas aminopeptidase to yield a polypeptide of the formula Y-Pro-Z, wherem X is one or more ammo acids except proline, Y is any ammo acid except prohne, and Z is one or more ammo acids. 17 The method of claim 16 wherein X is alanme 15 The method of claim 16 wherem " . is selected from the group consisting of phenylalanine, methionme, threonme, and aspartic acid. 19. The method of claim 18, wherem Y is phenylalanine. 20. The method of claim 16, wherem X is alanme and Y is phenylalanine. 21 The method of claim 19 or claim 20, wherem the precursor polypeptide is Ala-hGH

Inventors: TAYLOR DOUGLAS W, TOU JACOB S, TAYLOR, DOUGLAS, W., TOU, JACOB, S.
Applicants: MONSANTO CO, TAYLOR DOUGLAS W, TOU JACOB S, MONSANTO COMPANY, TAYLOR, DOUGLAS, W., TOU, JACOB, S.
Application year: 2000
Main classification: C12P21
IPC codes: C07K1, C07K14, C12P21