IMPROVED METHODS FOR THE PREPARATION OF ENDOTOXIN-BINDING PROTEINS

Abstract: Disclosed are improvements in methods for the isolation of endotoxin-binding proteins which are secreted by transfected host cells in appropriate cell culture media. In its preferred embodiment, the invention comprises addition of a cation exchange material to the media as the means of increasing the yield of recombinant endotoxin-binding proteins, such as bactericidal/permeability-increasing protein and lipopolysaccharide-binding protein.

Description: IMPROVED METHODS FOR THE PREPARATION OF E D0T0XIN-BINDIN6 PROTEINS This application is a continuation-in-part of U.S. Patent Application Serial No. 07/885,501, filed May 19, 1992. FIELD OF THE INVENTION The present invention generally relates to improved procedures for the preparation of endotoxin- binding proteins by recombinant methods and more particularly to processes for the large scale production of recombinant endotoxin-binding proteins, such as bactericidal/ permeability-increasing (BPI) protein, lipopolysaccharide-binding protein (LBP) , high density lipoprotein, Limulus anti-LPS factor, tachyplesin, and structurally related proteins using genetically transformed host cells grown in culture, including culture in fermentors. BACKGROUND OF THE INVENTION Endotoxin, or lipopolysaccharide, is a component of the cell wall of Gram-negative bacteria and is implicated in the manifestation of acute bacterial infections. Numerous proteins have been reported which bind to the principal form of endotoxin, lipopolysaccharide ("LPS") . Examples of such LPS -binding prote ins are bactericidal/permeability-increasing protein ("BPI protein") lipopolysaccharide-binding protein ("LBP") , incorporated by reference herein] , high density lipoprotein, and tachyplesin [Nakamura, et al . , J. Biol . Chem. , 263 : 16709-16713 (1988), incorporated by reference herein] . Certain of these proteins share significant structural homology. For example, both BPI and LBP possess a positively-charged a ino terminal region of approximately 25 Da which is the portion of each molecule which binds to the lipid A portion of LPS. See Schumann, et al .. Science, 249:1429-1431 (1990). Binding of BPI protein to membrane-bound LPS increases the envelope permeability of susceptible Gram negative bacteria. Ooi, et al . , J. Biol . Chem . , 252:14891 (1987). BPI protein also binds to soluble LPS and human BPI protein has been isolated from polymorphonuclear neutrophils ("PMΝs") by acid extraction combined with either ion exchange chromatography or E. coli affinity chromatography. Elsbach, et al . J. Biol . Chem. , 254:11000 (1979); Weiss et al . , Blood, 69: 652 (1987). The holo-BPI protein isolated from human PMΝs has potent bactericidal activity against a broad spectrum of Gram-negative bacteria. Elsbach, et al . , J. Biol . Chem., 254:11000 (1979). This antibacterial activity appears to be associated with the amino terminal region of the isolated human holo-BPI protein. In contrast, the carboxyl terminal region of the isolated hu an BPI protein displays only slightly detectable anti-bacterial activity. Ooi, et al . , J. Exp. Med. , 174 : 649 (1991). Human DNA encoding BPI has been cloned and the amino acid sequence of the encoded protein has been elucidated [See, Gray et al . , J. Biol . Chem . , 264 : 9505 (1989), hereinafter referred to as "Gray"; U.S. Letters Patent No. 5,198,541, both of which are incorporated by reference herein] allowing for the large scale production of recombinant BPI and biologically active (e.g. , amino and carboxy1 terminal) fragments thereof. Initial attempts to purify recombinant BPI and BPI-related proteins from the medium of transfected cells utilizing traditional protein purification methods provided low yields. Pulse-chase experiments using 35 S labelled methionine and performed c cell cultures of transfected Chinese Hamster Ovary HO) cells expressing a recombinant product comprising the amino terminal 199 amino acids of the mature BPI protein [hereinafter rBPI(1-199)] indicated that the recombinant BPI fragment disappeared from the media during 3.5 hours to 7 hours of chase. Preliminary experimental procedures aimed at determining the basis for this low product yield indicated that the protein product displays significant "stickiness" and, in fact, adheres to itself, to other media components (including host cells), and to plastic and glass culture vessels. However, the precise reason(s) for protein loss have yet to be elucidated. Like BPI protein, LBP binds to the lipid A portion of LPS. The holo-LBP protein is a 60 kD protein secreted by the liver and has been reported to be responsible for delivering LPS to macrophages. Ooi r et al . , J. Exp. Med. , 174 : 649-65 (1991). Unlike BPI protein, LBP generally enhances the inflammatory response generated by LPS. For example, LBP stimulates LPS-induced tumor necrosis factor ("TNF") production. Of interest to the present invention is the use of ion exchange materials in the isolation and purification of proteins and related substances. For example, published PCT application No. WO 89/05157 by Prior, et al . , reports the purification and isolation of recombinant immunoglobulins by passing the cell culture medium over a chromatography column, wherein the immunoglobulin is adsorbed onto an exchange material. The immunoglobulin is then eluted by raising the salt concentration in the column. As another example, published PCT application No. WO 90/08159 by Robins, et al . , reports removal of DNA from protein preparations by incubation in the presence of an anion exchange material. Wang, Ann. N.Y. Acad . Sci . , 413:313-321 (1983) presents the results of "hybrid" ermentation-extraction procedures for the production and isolation of a model antibiotic, cycloheximide, from fermentation cultures using non-ionic resins and noted that for one resin (XAD-4, Rohm and Haas, Philadelphia, PA) the product was absorbed on the resin surface making it "conceivable" to harvest the product from the resin. Due to the utility of endotoxin binding proteins such as BPI protein and LBP as regulators of bacterial infection and the sequelae thereof, there exists a need in the art for improved methods for the isolation of such proteins from cell culture media. BRIEF SUMMARY OF THE INVENTION The present invention provides improved methods which facilitate the isolation of endotoxin- binding proteins, and especially lipid A binding proteins, in high yields. The improved methods generally comprise the incorporation of a particulate cation exchange material into cell culture medium containing host cells which have been genetically transfected with DNA encoding the endotoxin-binding protein. Such proteins which are secreted into the cell culture medium by said host cells are reversibly bound to said cation exchange material. The cation exchange material with bound protein is then separated from the cell culture medium. Finally, the desired endotoxin-binding protein is then isolated from the cation exchange materi l. The improved methods comprise the incorporation of a particulate cation exchange material (preferably S-Sepharose particles) into a cell culture medium containing host cells (preferably CHO-K1 or CHO-DG44 cells) which have been genetically transformed with DNA for expression of endotoxin- binding proteins or fragments thereof. The protein secreted into the cell medium by said host cells is reversibly bound to said cation exchange material. The cation exchange material with bound protein is then separated from the cell culture medium. Finally, the protein is isolated from the cation exchange material. A presently preferred cation exchange material for practice of the invention is S-Sepharose and presently preferred isolation procedures comprise sequentially contacting the cation exchange material with a gradient or steps of increasing ionic strength. In a preferred embodiment of the invention, the improved methods are applied to the production of recombinant BPI products, including but not limited to, bactericidal/permeability-increasing protein and biologically active fragments thereof as well as BPI- related products such as fusion proteins comprising, at their amino terminal, the BPI protein or a biologically active fragment thereof and, at their carboxy terminal, at least one constant domain of an immunoglobulin heavy chain region or an allelic variant thereof. Proteins of interest are secreted by genetically transformed host cells which are grown and maintained in a culture medium suitable for growth of host cells and secretion of the protein products. Also, in another embodiment of the invention, the present improved methods are applied to the isolation of lipopolysaccharide-binding protein and amino-terminal fragments thereof. The foregoing brief summary illustrates the preferred embodiments of the invention. Numerous aspects and advantages of the present invention will become apparent to the skilled artisan upon reading the following detailed description thereof. DESCRIPTION OF THE DRAWING FIG. 1 depicts the results of comparative experiments using methods according to the invention and traditional chromatography methods to isolate the rBPI(1-199) protein. FIG. 2 depicts the results of the stepwise elution of rBPI(1-99) from S-Sepharose. FIG. 3 depicts results of Western blot analysis of products prepared according to the invention. FIG. 4 is a Western blot depicting rBPI-Ig fusion products prepared according to the methods of the present invention. FIG. 5 depicts the results of a Coomassie- stained gel depicting isolation of LBP prepared according to methods of the present invention. -7a- maintained in a culture medium suitable for growth of host cells and secretion of the protein products. Also, in another embodiment of the invention, the present improved methods are applied to the isolation of lipopolysaccharide-binding protein and amino-terminal fragments thereof. The foregoing brief summary illustrates the preferred embodiments of the invention. Numerous aspects and advantages of the present invention will become apparent to the skilled artisan upon reading the following detailed description thereof. DESCRIPTION OF THE DRAWING FIGS. 1A, IB, 1C and ID depict the results of comparative experiments using methods according to the invention and traditional chromatography methods to isolate the rBPI(1-199) protein. FIG. 2 depicts the results of the stepwise elution of rBPI(1-99) from S-Sepharose. FIG. 3 depicts results of Western blot analysis of products prepared according to the invention. FIG. 4 is a Western blot depicting rBPI-Ig fusion products prepared according to the methods of the present invention. FIG. 5 depicts the results of a Coomassie-stained gel depicting isolation of LBP prepared according to methods of the present invention. SUBSTITUTESHEET ISA/EP -8- DETAILED DESCRIPTION OF THE INVENTION The following detailed description illustrates practice of methods of the invention in the context of recombinant production of three particular endotoxin-binding proteins, an amino- terminal portion of recombinant BPI protein ("rBPI protein") , an amino-terminal portion of recombinant LBP ("rLBP") , and rBPI-immunoglobulin fusion proteins ("rBPI-Ig fusions") from animal cell cultures. While the practice of the invention is exemplified herein by certain specific endotoxin-binding proteins, it is apparent to the skilled artisan that, due to their general structural and functional similarities, any endotoxin-binding protein may be isolated using methods of the invention. Such proteins include, but are not limited to, polymyxin B, high density lipoprotein, Limulus anti-LPS factor, and tachyplesin. More specifically, Example 1 demonstrates that addition of the cation exchange material, S- Sepharose, to a cell culture medium results in increased yields of rBPI protein. Example 2 provides further results which demonstrate that introduction of the cation exchange material to cell cultures produces increased yields of rBPI protein. Example 3 illustrates practice of the improved methods in the isolation of rBPI-immunoglobulin fusion proteins and Example 4 demonstrates the use of a cation exchange material in the isolation of LBP. -9- Example 1 Isolation of recombinant BPI products Methods of the present invention were used to isolate a recombinant BPI protein which is the expression product of DNA encoding the 31-residue signal sequence and the first 199 amino acids of the N-terminus of the mature human BPI, as set out in SEQ ID NOS: 1 and 2 and is designated "rBPI(1-199)" herein. The DNA sequence employed differs from the BPI-encoding DNA sequence reported in Gray, et al . , supra, in that the valine at position 151 of the rBPI(1-199) expression product is specified by GTG rather than by GTC as in Gray et al . and rBPI(1-199) encodes glutamic acid (specified by GAG) at position 185 rather than lysine (specified by AAG) as reported at that position in Gray et al . Recombinant production of rBPI(1-199) protein is reported in Gazzano-Santoro, et al . , Infection and Immunity, 60 : 4754-4761 (1992) , wherein the protein is referred to as "rBPI-23". The host cells employed in this example were CHO-K1 cells transformed with a DNA vector including DNA encoding the initial 199 amino terminal amino acids of human BPI preceded by its endogenous 31 residue secretory signal sequence. The desired expression product, rBPI(1-199), was a biologically active fragment of the human BPI protein comprising the initial 199 amino terminal residues from which the signal sequence residues were removed in the course of -10- post-translational secretory processing by the host cells. Two roller bottles containing the transfected CHO host cells in Hams-' F12 medium supplemented with 5% fetal bovine serum were prepared and the cells were grown to confluence (approximately 3 days) . Once confluency was reached, the Hams F12 medium was removed and replaced with 500 ml of HB-CHO serum free medium (Irvine Scientific, Irvine, Ca.). In the first roller bottle, approximately 8 gm (wet weight) of sterilized S-Sepharose (Pharmacia, fast flow, #17-0511-01, Uppsula, Sweden) was added to one of the roller bottles for 3 days. The S-Sepharose was then isolated in order to generate a first column. Growth medium and S-Sepharose resin were removed from roller bottles, pooled and left for at least 15 minutes to allow the S-Sepharose to settle to the bottom of the container. The bulk of the medium, clear of resin, was removed by decanting and then filtered through a device, such as a fritted disc, to permit the removal of cells and the retention of the S-Sepharose. Following the decanting of the medium, the S-Sepharose was suspended in an Acetate buffer comprising 20 mM sodium acetate/acetic acid at pH 4.0 containing 0.1 M NaCl, stirred gently, and allowed to settle for 10 minutes. The buffer was then decanted and the S-Sepharose was transferred in a small volume to an appropriately-sized liquid chromatography column (1 x 10 cm, Econocolumn, BioRad, Richmond, CA) . -11- The second roller bottle contained cells grown under the conditions stated above but in the absence of S-Sepharose. The medium from this second roller bottle was removed from the roller bottle. CHO cells were removed by centrifugation and the clarified medium was adjusted to contain 20 mM sodium acetate/acetic acid, pH 4.0. The medium was diluted to a conductivity of 10-15 mS/cm and was then loaded onto a second, traditional S-Sepharose column which had been equilibrated in 20 mM sodium acetate/acetic acid pH 4.0 (Acetate buffer) containing 0.1 M NaCl in order to maximize binding of the rBPI(1-199) protein. Both the first and the second S-Sepharose columns were washed with 0.1 M NaCl-Acetate buffer until the A280 absorbance of the eluate was equal to that of the 0.1 M NaCl-Acetate buffer alone. The protein bound to each column was then eluted in a single step with 1.0 M NaCl-Acetate buffer. The eluates from both columns were subjected to an ELISA assay wherein samples from the eluates were bound to Immulon-2 flat bottom multiwell plates (Dynetech Labs) in the presence of PBS overnight at 4°C. The plates were then washed with 0.05% Tween-20 in PBS, and then incubated with a 1:1000 dilution of rabbit anti-rBPI(1-199) antisera in PBS containing 0.05% Tween-20 for one hour at room temperature. After incubation, the plate was again washed with 0.05% Tween-20 in PBS and the ELISA was developed using the TMB reagent (Pierce Rockford, IL) according -12- to the manufactures instructions and read at 450 nm in an EL309 microplate reader (Biotek Instruments, Winooski Vt.) . The ELISA results revealed that the eluate from the S-Sepharose column derived from the cell culture medium produced 3-8 fold stronger reactivity compared to the eluate from the S-Sepharose column to which medium had been added. Example 2 provides further results, demonstrating that culturing S-Sepharose together with transfected CHO cells increased the yield of rBPI(l- 199) protein produced by the transfected cells. Example 2 Quantitative Analysis of Isolation or rBPI (1-199) In order to more quantitatively demonstrate that the yield of the rBPI(1-199) protein product obtained from the CHO cell cultures in Example 1 was greater when a cation exchange material was added to the cell culture medium, stained gel and Western analyses were carried out on the eluate samples described above. Protein samples obtained from the 1.0 M NaCl-Acetate buffer eluates described in Example 1 were separated by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) . The samples of rBPI(l- 199) were first adjusted to contain less than 0.5 M NaCl and were then precipitated by the addition of ice-cold acetone to a final concentration of 75%. The -13- resulting protein precipitate was then pelleted by centrifugation at greater than 10,000 rpm for 5 to 10 minutes. The supernatant was removed and the precipitate was suspended in a gel sample buffer containing 8 M Urea, 2% SDS, 60 mM Tris HC1 at pH 6.8. The suspended samples and appropriate protein molecular weight standards (BioRad, Richmond, CA and BRL, Bethesda, MD) were heated to 95 * C for 3-5 minutes and then loaded onto uniform percentage or gradient percentage polyacrylamide gels (BioRad) and separated using a mini Protean II gel electrophoresis apparatus (BioRad) . Following electrophoresis the gels were used directly for Coomassie staining (0.5% Coomassie Brilliant Blue-R, 25% isopropanol, 10% methanol, 10% acetic acid) or were used for electrotransfer. The proteins which were separated by SDS-PAGE were electrotransferred along with appropriate prestain standard protein (BioRad) onto either nitrocellulose (BA85, Schleicher and Schuell, Keene, NH) or PVDF (Immobilon-P, Millipore, Bedford, MA) membranes. The transfer was achieved in 10% CAPS (cyclohexylamino-1- propane-sulfonic acid), 10% methanol, pH 11.5 for 20 minutes at 0.5 amps. The resulting blots were processed using a 1:1000 dilution of rabbit anti-human BPI (holoprotein) antisera and the Western Lite Chemiluminescent Detection System (Tropix System, Bedford, MA) according to the manufacturer's instructions. Gelatin (BioRad) at 0.25% was used in place of Tropix I-Block and the membranes were not -14- dried following electrotransfer. The processed membranes were exposed to Cronex 4 film (Dupont, Wilmington, DE) . The results of the stained gel and Western analysis are shown in Fig. 1, wherein quadrants A and B respectively present coomassie stain and Western blot analysis of the flow through (FT) , 0.1 M NaCl and 1.0 M NaCl eluates of columns formed from S-Sepharose beads incubated with culture medium. Quadrants C and D correspondingly present Coomassie stain and Western blot analysis of eluates from "traditional" columns of S-Sepharose. The arrow in quadrants A and C indicates the region corresponding the molecular weight of the rBPI(1-199) protein product. The yield of rBPI(l- 199) protein was estimated to be at least 10-fold higher when the cationic exchange resin, S-Sepharose, had been added to the culture medium during cell growth. Subsequent experiments involved the isolation of rBPI(1-199) from 20 to 40 g of S- Sepharose obtained from 3 to 5 roller bottles. The bound samples were eluted with increasing concentrations of NaCl in Acetate buffer. As shown in Fig. 2, the rBPI(1-199) product, visualized by Coomassie blue staining, is seen as a 23 kd protein in the 0.8, 0.9, 1.0, and 1.5 M NaCl-Acetate buffer eluates from the S-Sepharose columns. Little or no rBPI(1-199) protein was observed in the 0.2 M to 0.7 M NaCl-Acetate buffer eluates. The results of the -14a- dried following electrotransfer. The processed membranes were exposed to Cronex 4 film (Dupont, Wilmington, DE) . The results of the stained gel and Western analysis are shown in Figs. 1A-1D, wherein Fig. 1A and IB respectively present coomassie stain and Western blot analysis of the flow through (FT), 0.1 M NaCl and 1.0 M NaCl eluates of columns formed from S-Sepharose beads incubated with culture medium. Figs. 1C and ID correspondingly present Coomassie stain and Western blot analysis of eluates from "traditional" columns of S- Sepharose. The arrow in Figs. 1A and 1C indicates the region corresponding the molecular weight of the rBPI(l- 199) protein product. The yield of rBPI(1-199) protein was estimated to be at least 10-fold higher when the cationic exchange resin, S-Sepharose, had been added to the culture medium during cell growth. Subsequent experiments involved the isolation of rBPI(1-199) from 20 to 40 g of S-Sepharose obtained from 3 to 5 roller bottles. The bound samples were eluted with increasing concentrations of NaCl in Acetate buffer. As shown in Fig. 2, the rBPI(1-199) product, visualized by Coomassie blue staining, is seen as a 23 kd protein in the 0.8, 0.9, 1.0, and 1.5 M NaCl-Acetate buffer eluates from the S-Sepharose columns. Little or no rBPI(1-199) protein was observed in the 0.2 M to 0.7 M NaCl-Acetate buffer eluates. The results of the SUBSTITUTESHEET ISA/EP -15- Western Blot (Figure 3) indicated that the strongest detectable rBPI(1-199) protein signal was obtained in the 0.8 M to 1.0 M NaCl-Acetate buffer eluates of the S-Sepharose columns. The 1.5 M NaCl eluate from the S-Sepharose column also contained protein which was identified as rBPI(l-199) (See Figure 2, right lane). The 1.5 M NaCl-Acetate buffer eluate from the S-Sepharose column contained protein having molecular weights of approximately 40 kDa and greater than 66 kDa (Fig. 2) which, upon treatment with dithiothreitol, could be reduced to a single band of approximately 23 kDa. The reduced protein was cross-reactive with anti-BPI antisera and had the N-terminal sequence of correctly processed rBPI(1-199). The 40 kDa and greater than 66 kDa proteins appear to be disulfide-linked multimers of rBPI(1-199) . The aforementioned results indicate that the addition of a cation exchange material to the cell culture medium improved recovery of rBPI(1-199) protein. In order to determine optimum concentration of S-Sepharose, 1.25 g to 10 g quantities of S- Sepharose were added to roller bottles containing 500 ml culture medium and transfected CHO cells and allowed to incubate as described above. The medium containing the cation exchange material was then poured into columns as described above. The columns were washed with 0.1 M NaCl-Acetate buffer, then with 0.7 M NaCl-Acetate buffer and the rBPI(1-199) sample -16- was eluted with 1.0 M NaCl-Acetate buffer. The yield of rBPI(1-199) was determined by chromatography on C4 reverse phase HPLC and was essentially constant for 2.5 g, 5.0 g, and 10 g quantities of S-Sepharose. The yield was decreased by approximately 50% in roller bottles containing only 1.25 g S-Sepharose per roller bottle. Example 3 provides results demonstrating that increased yield of rBPI fusion proteins is obtained using methods according to the present invention. EXAMPLE 3 Isolation of rBPI-Iσ Fusion Proteins Host cells employed in this example are CHO- DG44 cells transfected with a DNA vector comprising DNA encoding the initial 199 amino acids of BPI protein fused to at least one constant region of an immunoglobulin heavy chain. Construction of such "rBPI fusions" is provided in co-pending, co-owned U.S. Patent Application Serial No. 07/885,911, as well as co-pending, co-owned, concurrently-filed continuation-in-part application serial no. (Attorney Docket No. 27129/31429, both of which are incorporated by reference herein. Transfected CHO-DG44 cells were grown in roller bottles. For each roller bottle, a T150 flask (containing 50 ml α-MEM without nucleosides and 10% dialyzed fetal bovine serum) was inoculated with transfected cells and the cells were grown to confluence (approximately 3-4 days) . The -17- cells were then trypsinized and transferred into a 900cm 2 roller bottle containing 500 ml Ham's F12 media and 10% fetal bovine serum and grown to confluence for approximately 3 days. Once confluency was reached, the Ham's F12 medium was removed and replaced with 500 ml HB-CHO serum-free medium (Irvine Scientific, Irvine, CA) . S-Sepharose beads, which had first been washed with Dulbecco's phosphate buffered saline (PBS) and autoclaved for 20 minutes at 120°C were added aseptically to the roller bottles. The cells were then incubated at 37 * C for 3 days, at which time the beads and growth medium were removed and left undisturbed for at least 15 minutes. The bulk of the medium, clear of resin, was removed from by decanting and filtered through a device, such as a fritted disc, which allows removal of the cells and retention of the S-Sepharose. Following the decanting of the medium, the S-Sepharose was suspended in an acetate buffer comprising 20 mM sodium acetate/acetic acid, 0.1 M NaCl at pH 4.0, stirred gently, and allowed to settle for 10 minutes. The buffer was then decanted and the S-Sepharose was transferred in a small volume to an appropriately-sized liquid chromatography column. An Econocolumn (2.5 x 10 cm, BioRad, Richmond, CA) was used for a 20 to 40 g pooled sample of S-Sepharose collected from 3 to 5 roller bottles. The packed S- Sepharose column was washed with 0.1 M NaCl-acetate buffer until the A280 absorbance of the eluate was -18- equal to that of the 0.1 M NaCl-acetate buffer alone, with 0.5 M NaCl-acetate buffer, with 1.0 M NaCl- acetate buffer and again with 1.5 M NaCl-acetate buffer. Additional CHO-DG44 cells were prepared as above except that S-Sepharose beads were not added to the culture medium. Instead, an attempt was made to purify the rBPI fusion expression product utilizing two different protein A columns. A first sample of HB-CHO medium (see above) was filtered through a 0.45 μ filter in order to separate the CHO-DG44 cells from the rest of the medium. The sample was than adjusted to pH 8.0 and placed on a ProSepA (Bioprocessing) column. A second preparation was placed on an AvidGel (Bioprocessing) column. The elution of both columns was performed with 25 mM citrate buffer at pH 5.5. No rBPI fusion product was recovered from either protein A column. Nor was any product visualized from the ProSepA column following reduction (Figure 4, lane 1) . However, when the ProSepA and Avidgel columns were stripped with 100 mM citrate buffer at pH 3.0, rBPI fusion protein was detected as shown respectively in lanes 2 and 3 of Figure 4. Lanes 4-6 of Figure 4 represent the 0.5 M, 1.0 M, and 1.5 M eluates from the S-Sepharose column. Of the eluates from the S- Sepharose column, the 1.5 M eluate contained material corresponding to a fusion dimer of approximately 100 kD. -19- Example 4 provides results demonstrating that increased product yield of LBP is also obtained when cells transfected with DNA encoding LBP are incubated with a cation exchange resin. EXAMPLE 4 Isolation Of Lipopolvsaccharide-Binding Protein The DNA sequence obtained for the 25 kD amino terminal of LBP is shown in SEQ ID NO: 3. That sequence differs in two regions from the reported sequence of Schumann, et al . , Science, 249 : 1429-1431 (1990) (SEQ ID NO: 4) . Those differences lead to amino acid differences at positions 129-132 and at position 149 (an asparagine residue at position 148 is encoded by GAT in Schumann, supra and by GAC in SEQ ID NO: 3). See also, published PCT Application 93/06228. Host cells employed in this example are CHO- DG44 cells transfected with a DNA vector comprising DNA encoding the initial 197 amino acids of LBP, the expression product. Transfected DG44 cells were grown in roller bottles. For each roller bottle, a T150 flask (containing 50 ml α-MEM without nucleosides and 10% dialyzed fetal bovine serum) was inoculated with transfected cells and the cells were grown to confluence (approximately 3-4 days) . The cells were then trypsinized and transferred into a 900cm 2 roller bottle containing 500 ml Ham's F12 media and 10% fetal bovine serum and grown to confluence for approximately -20- 3 days. Once confluency was reached, the Ham's F12 medium was removed and replaced with 500 ml HB-CHO serum-free medium (Irvine Scientific, Irvine, CA) . S-Sepharose beads, which had first been washed with PBS and autoclaved for 20 minutes at 120 C were added aseptically to the roller bottles. The cells were then incubated at 37 C for 3 days, at which time the beads and growth medium were removed and left undisturbed for at least 15 minutes. The bulk of the medium, clear of resin, was removed from by decanting and filtered through a device, such as a fritted disc, which allows removal of the cells and retention of the S-Sepharose. Following the decanting of the medium, the S-Sepharose was suspended in an acetate buffer comprising 20 mM sodium acetate/acetic acid, 0.1 M NaCl at pH 4.0, stirred gently, and allowed to settle for 10 minutes. The buffer was then decanted and the S-Sepharose was transferred in a small volume to an appropriately-sized liquid chromatography column. An Econocolumn (2.5 x 10 cm, BioRad, Richmond, CA) was used for a 20 to 40 g pooled sample of S-Sepharose collected from 3 to 5 roller bottles. The packed S- Sepharose column was washed with 0.1 M NaCl-acetate buffer until the A280 absorbance of the eluate was equal to that of the 0.1 M NaCl-acetate buffer alone, with 0.7 M NaCl-acetate buffer and again with 1.0 M NaCl-acetate buffer. Yield of rLBP from cell cultures in which S- Sepharose beads were added is shown in Figure 5 which -21- is a Coomassie-stained gel of the 0.7 M (lanes 1 and 3) and 1.0 M (lanes 2 and 4) eluates described above. As shown in the figure, a significant amount of LBP eluted at 1.0 M. That S-Sepharose is able to facilitate LBP production from cell cultures is unexpected based on its calculated pi (6.6). In the culture medium used above, in which the pH was approximately 7.0, LBP would be expected, based on its pi, to be uncharged or slightly negatively charged and thus unr : .ctive with a cation exchange resin, such as S-Sephai se. Numerous modifications and variations in the practice of the invention are expected to occur to those skilled in the art upon consideration of the foregoing description of the presently preferred embodiments thereof. For example, the concentration of cation exchange material used in the invention may be varied according to the number and type (i.e., efficiency of production of the recombinant product) of cells used. As another example, while cation exchange materials other than S-Sepharose [e.g., Biorex 70, and SP (sulfopropyl) type materials such as SP-Sephadex as well as CM (carboxymethyl) type materials such as CM Sepharose and CM Sephadex] can be employed in processes of the invention, S-Sepharose was preferred as being most readily handled, subjected to sterilization processing, and the like. As still another example, while the above illustrative examples address recombinant production of endotoxin binding -22- proteins in roller bottles, processes of the invention are readily "scaled up" to production in fermentors. Typical fermentation conditions for such processes as applied to production of rBPI(1-199) include use of a 600L working volume in a 750L Chemap (Woodbury, N.Y.) fermentor wherein CHO-K1 cells transfected with plasmid pING4502 [see, Gazzano et al . , supra) are grown in ExCell 301 Medium (JRH Scientific) supplemented with 0.05% FBS and 0.01% Antifoam (U Carferm Adjuvant 27, Union Carbide) and 1% SP Sepharose "big beads" (100-300 micron diameter, Pharmacia) is added. Finally, the precise elution profiles of recombinant endotoxin-binding proteins isolated according to the invention are expected to vary depending on the precise identity of the protein involved. As one example, rBPI(1-199) is readily isolated from resin beads following a 0.7 M NaCl- Acetate buffer wash. However, yields of cysteine replacement analogs of BPI protein such as described in co-owned, co-pending U.S. Patent Application Serial No. 08/013,801 by Theofan et al . are enhanced by isolation following a 0.6 M NaCl-Acetate buffer wash. Consequently, the only limitations which should be placed upon the scope of the present invention are those which appear in the appended claims. -23- SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: Grinna, Lynn (ii) TITLE OF INVENTION: Improved Methods for the Preparation of Endotoxin-Binding Proteins (iii) NUMBER OF SEQUENCES: 4 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Marshall, O'Toole, Gerstern, Murray & Borun (B) STREET: 6300 Sears Tower, 233 South Wacker Drive (C) CITY: Chicago (D) STATE: Illinois (E) COUNTRY: USA (F) ZIP: 60606-6402 (V) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: Patentln Release #1.0, Version #1.25 (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: (B) FILING DATE: (C) CLASSIFICATION: (vii) PRIOR APPLICATION DATA: (A) APPLICATION NUMBER: US 07/885,501 (B) FILING DATE: 19-MAY-1992 (viii) ATTORNEY/AGENT INFORMATION: (A) NAME: Meyers, Thomas C. (B) REGISTRATION NUMBER: 36,989 (C) REFERENCE/DOCKET NUMBER: 31405 (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: 312/474-6300 (B) TELEFAX: 312/474-0448 (C) TELEX: 25-3856 (2) INFORMATION FOR SEQ ID NO:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1813 base pairs (B) TYPE: nucleic acid -24- (C) STRANDEDNESS: single (D) TOPOLOGY: linear Cii) MOLECULE TYPE: cDNA (ix) FEATURE: CA) NAME/KEY: CDS (B) LOCATION: 31..1491 (ix) FEATURE: (A) NAME/KEY: mat_peptide (B) LOCATION! 124..1491 (xi) SEQUENCE DESCRIPTION: SEQ ID NO:l: CAGGCCTTGA GGTTTTGGCA GCTCTGGAGG ATG AGA GAG AAC ATG GCC AGG GGC 54 Met Arg Glu Asn Met Ala Arg Gly -31 -30 -25 CCT TGC AAC GCG CCG AGA TGG GTG TCC CTG ATG GTG CTC GTC GCC ATA 102 Pro Cys Asn Ala Pro Arg Trp Val Ser Leu Met Val Leu Val Ala lie -20 -15 -10 GGC ACC GCC GTG ACA GCG GCC GTC AAC CCT GGC GTC GTG GTC AGG ATC 150 Gly Thr Ala Val Thr Ala Ala Val Asn Pro Gly Val Val Val Arg lie -5 1 5 TCC CAG AAG GGC CTG GAC TAC GCC AGC CAG CAG GGG ACG GCC GCT CTG 198 Ser Gin Lys Gly Leu Asp Tyr Ala Ser Gin Gin Gly Thr Ala Ala Leu 10 15 20 25 CAG AAG GAG CTG AAG AGG ATC AAG ATT CCT GAC TAC TCA GAC AGC TTT 246 Gin Lys Glu Leu Lys Arg lie Lys lie Pro Asp Tyr Ser Asp Ser Phe 30 35 40 AAG ATC AAG CAT CTT GGG AAG GGG CAT TAT AGC TTC TAC AGC ATG GAC 294 Lys lie Lys His Leu Gly Lys Gly His Tyr Ser Phe Tyr Ser Met Asp 45 SO 55 ATC CGT GAA TTC CAG CTT CCC AGT TCC CAG ATA AGC ATG GTG CCC AAT 342 lie Arg Glu Phe Gin Leu Pro Ser Ser Gin lie Ser Met Val Pro Asn 60 65 70 GTG GGC CTT AAG TTC TCC ATC AGC AAC GCC AAT ATC AAG ATC AGC GGG 390 Val Gly Leu Lys Phe Ser lie Ser Asn Ala Asn lie Lys lie Ser Gly 75 80 85 AAA TGG AAG GCA CAA AAG AGA TTC TTA AAA ATG AGC GGC AAT TTT GAC 438 Lys Trp Lys Ala Gin Lys Arg Phe Leu Lys Met Ser Gly Asn Phe Asp 90 95 100 105 -25- CTG AGC ATA GAA GGC ATG TCC ATT TCG GCT GAT CTG AAG CTG GGC AGT 486 Leu Ser lie Glu Gly Met Ser lie Ser Ala Asp Leu Lys Leu Gly Ser 110 115 120 AAC CCC ACG TCA GGC AAG CCC ACC ATC ACC TGC TCC AGC TGC AGC AGC 534 Asn Pro Thr Ser Gly Lys Pro Thr lie Thr Cys Ser Ser Cys Ser Ser 125 130 135 CAC ATC AAC AGT GTC CAC GTG CAC ATC TCA AAG AGC AAA GTG GGG TGG 582 His lie Asn Ser Val His Val His lie Ser Lys Ser Lys Val Gly Trp 140 145 150 CTG ATC CAA CTC TTC CAC AAA AAA ATT GAG TCT GCG CTT CGA AAC AAG 630 Leu lie Gin Leu Phe His Lys Lys lie Glu Ser Ala Leu Arg Asn Lys 155 160 165 ATG AAC AGC CAG GTC TGC GAG AAA GTG ACC AAT TCT GTA TCC TCC GAG 678 Met Asn Ser Gin Val Cys Glu Lys Val Thr Asn Ser Val Ser Ser Glu 170 175 180 185 CTG CAA CCT TAT TTC CAG ACT CTG CCA GTA ATG ACC AAA ATA GAT TCT 726 Leu Gin Pro Tyr Phe Gin Thr Leu Pro Val Met Thr Lys lie Asp Ser 190 195 200 GTG GCT GGA ATC AAC TAT GGT CTG GTG GCA CCT CCA GCA ACC ACG GCT 774 Val Ala Gly lie Asn Tyr Gly Leu Val Ala Pro Pro Ala Thr Thr Ala 205 210 215 GAG ACC CTG GAT GTA CAG ATG AAG GGG GAG TTT TAC AGT GAG AAC CAC 822 Glu Thr Leu Asp Val Gin Met Lys Gly Glu Phe Tyr Ser Glu Asn His 220 225 230 CAC AAT CCA CCT CCC TTT GCT CCA CCA GTG ATG GAG TTT CCC GCT GCC 870 His Asn Pro Pro Pro Phe Ala Pro Pro Val Met Glu Phe Pro Ala Ala 235 240 245 CAT GAC CGC ATG GTA TAC CTG GGC CTC TCA GAC TAC TTC TTC AAC ACA 918 His Asp Arg Met Val Tyr Leu Gly Leu Ser Asp Tyr Phe Phe Asn Thr 250 255 260 265 GCC GGG CTT GTA TAC CAA GAG GCT GGG GTC TTG AAG ATG ACC CTT AGA 966 Ala Gly Leu Val Tyr Gin Glu Ala Gly Val Leu Lys Met Thr Leu Arg 270 275 280 GAT GAC ATG ATT CCA AAG GAG TCC AAA TTT CGA CTG ACA ACC AAG TTC 1014 Asp Asp Met lie Pro Lys Glu Ser Lys Phe Arg Leu Thr Thr Lys Phe 285 290 295 TTT GGA ACC TTC CTA CCT GAG GTG GCC AAG AAG TTT CCC AAC ATG AAG 1062 Phe Gly Thr Phe Leu Pro Glu Val Ala Lys Lys Phe Pro Asn Met Lys 300 305 310 -26- ATA CAG ATC CAT GTC TCA GCC TCC ACC CCG CCA CAC CTG TCT GTG CAG 1110 lie Gin lie His Val Ser Ala Ser Thr Pro Pro His Leu Ser Val Gin 315 320 325 CCC ACC GGC CTT ACC TTC TAC CCT GCC GTG GAT GTC CAG GCC TTT GCC 1158 Pro Thr Gly Leu Thr Phe Tyr Pro Ala Val Asp Val Gin Ala Phe Ala 330 335 340 345 GTC CTC CCC AAC TCC TCC CTG GCT TCC CTC TTC CTG ATT GGC ATG CAC 1206 Val Leu Pro Asn Ser Ser Leu Ala Ser Leu Phe Leu lie Gly Met His 350 355 360 ACA ACT GGT TCC ATG GAG GTC AGC GCC GAG TCC AAC AGG CTT GTT GGA 1254 Thr Thr Gly Ser Met Glu Val Ser Ala Glu Ser Asn Arg Leu Val Gly 365 370 375 GAG CTC AAG CTG GAT AGG CTG CTC CTG GAA CTG AAG CAC TCA AAT ATT 1302 Glu Leu Lys Leu Asp Arg Leu Leu Leu Glu Leu Lys His Ser Asn He 380 385 390 GGC CCC TIC CCG GTT GAA TTG CTG CAG GAT ATC ATG AAC TAC ATT GTA 1350 Gly Pro Phe Pro Val Glu Leu Leu Gin Asp lie Met Asn Tyr He Val 395 400 405 CCC ATT CTT GTG CTG CCC AGG GTT AAC GAG AAA CTA CAG AAA GGC TTC 1398 Pro He Leu Val Leu Pro Arg Val Asn Glu Lys Leu Gin Lys Gly Phe 410 415 420 425 CCT CTC CCG ACG CCG GCC AGA GTC CAG CTC TAC Pro Leu Pro Thr Pro Ala Arg Val Gin Leu Tyr 430 435 CCT CAC CAG AAC TTC CTG CTG TTC GGT GCA GAC Pro His Gin Asn Phe Leu Leu Phe Gly Ala Asp 445 450 TGAAGGCACC AGGGGTGCCG GGGGCTGTCA GCCGCACCTG ACCGGCTGCC TTTCCCCAGG GAATCCTCTC CAGATCTTAA TCTTCGACTC AGATTCAGAA ATGATCTAAA CACGAGGAAA CATGGTGTGT ATTTTAGGGA TTATGAGCTT CTTTCAAGGG CCTCCAGGAA TCGTGTTTCA ATTGTAACCA AGAAATTTCC AACTTCTGGT TTTTTTCATG TG (2) INFORMATION FOR SEQ ID NO:2: Ci) SEQUENCE CHARACTERISTICS: -27- (A) LENGTH: 487 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2: Met Arg Glu Asn Met Ala Arg Gly Pro Cys Asn Ala Pro Arg Trp Val -31 -30 -25 -20 Ser Leu Met Val Leu Val Ala He Gly Thr Ala Val Thr Ala Ala Val -15 -10 -5 1 Asn Pro Gly Val Val Val Arg He Ser Gin Lys Gly Leu Asp Tyr Ala 5 10 15 Ser Gin Gin Gly Thr Ala Ala Leu Gin Lys Glu Leu Lys Arg He Lys 20 25 30 He Pro Asp Tyr Ser Asp Ser Phe Lys He Lys His Leu Gly Lys Gly 35 40 45 His Tyr Ser Phe Tyr Ser Met Asp He Arg Glu Phe Gin Leu Pro Ser 50 55 60 65 Ser Gin He Ser Met Val Pro Asn Val Gly Leu Lys Phe Ser He Ser 70 75 80 Asn Ala Asn He Lys He Ser Gly Lys Trp Lys Ala Gin Lys Arg Phe 85 90 95 Leu Lys Met Ser Gly Asn Phe Asp Leu Ser He Glu Gly Met Ser He 100 105 110 Ser Ala Asp Leu Lys Leu Gly Ser Asn Pro Thr Ser Gly Lys Pro Thr 115 120 125 He Thr Cys Ser Ser Cys Ser Ser His He Asn Ser Val His Val His 130 135 140 145 He Ser Lys Ser Lys Val Gly Trp Leu He Gin Leu Phe His Lys Lys 150 155 160 He Glu Ser Ala Leu Arg Asn Lys Met Asn Ser Gin Val Cys Glu Lys 165 170 175 Val Thr Asn Ser Val Ser Ser Glu Leu Gin Pro Tyr Phe Gin Thr Leu 180 185 190 Pro Val Met Thr Lys He Asp Ser Val Ala Gly He Asn Tyr Gly Leu 195 200 205 -28- Val Ala Pro Pro Ala Thr Thr Ala Glu Thr Leu Asp Val Gin Met Lys 210 215 220 225 Gly * Glu Phe Tyr Ser Glu Asn His His Asn Pro Pro Pro Phe Ala Pro 230 235 240 Pro Val Met Glu Phe Pro Ala Ala His Asp Arg Met Val Tyr Leu Gly 245 250 255 Leu Ser Asp Tyr Phe Phe Asn Thr Ala Gly Leu Val Tyr Gin Glu Ala 260 265 270 Gly Val Leu Lys Met Thr Leu Arg Asp Asp Met He Pro Lys Glu Ser 275 280 285 Lys Phe Arg Leu Thr Thr Lys Phe Phe Gly Thr Phe Leu Pro Glu Val 290 295 300 305 Ala Lys Lys Phe Pro Asn Met Lys He Gin He His Val Ser Ala Ser 310 315 320 Thr Pro Pro His Leu Ser Val Gin Pro Thr Gly Leu Thr Phe Tyr Pro 325 330 335 Ala Val Asp Val Gin Ala Phe Ala Val Leu Pro Asn Ser Ser Leu Ala 340 345 350 Ser Leu Phe Leu He Gly Met His Thr Thr Gly Ser Met Glu Val Ser 355 360 365 Ala Glu Ser Asn Arg Leu Val Gly Glu Leu Lys Leu Asp Arg Leu Leu 370 375 380 385 Leu Glu Leu Lys His Ser Asn He Gly Pro Phe Pro Val Glu Leu Leu 390 395 400 Gin Asp He Met Asn Tyr He Val Pro He Leu Val Leu Pro Arg Val 405 410 415 Asn Glu Lys Leu Gin Lys Gly Phe Pro Leu Pro Thr Pro Ala Arg Val 420 425 430 Gin Leu Tyr Asn Val Val Leu Gin Pro His Gin Asn Phe Leu Leu Phe 435 440 445 Gly Ala Asp Val Val Tyr Lys 450 455 (2) INFORMATION FOR SEQ ID NO:3r (i) SEQUENCE CHARACTERISTICSr (A) LENGTH: 591 base pairs -29- (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 1..591 (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3: GCC AAC CCC GGC TTG GTC GCC AGG ATC ACC GAC AAG GGA CTG CAG TAT 48 Ala Asn Pro Gly Leu Val Ala Arg He Thr Asp Lys Gly Leu Gin Tyr 1 5 10 15 GCG GCC CAG GAG GGG CTA TTG GCT CTG CAG AGT GAG CTG CTC AGG ATC 96 Ala Ala Gin Glu Gly Leu Leu Ala Leu Gin Ser Glu Leu Leu Arg He 20 25 30 ACG CTG CCT GAC TTC ACC GGG GAC TTG AGG ATC CCC CAC GTC GGC CGT 144 Thr Leu Pro Asp Phe Thr Gly Asp Leu Arg He Pro His Val Gly Arg 35 40 45 GGG CGC TAT GAG TTC CAC AGC CTG AAC ATC CAC AGC TGT GAG CTG CTT 192 Gly Arg Tyr Glu Phe His Ser Leu Asn He His Ser Cys Glu Leu Leu 50 55 60 CAC TCT GCG CTG AGG CCT GTC CCC GGC CAG GGC CTG AGT CTC AGC ATC 240 His Ser Ala Leu Arg Pro Val Pro Gly Gin Gly Leu Ser Leu Ser He 65 70 75 80 TCC GAC TCC TCC ATC CGG GTC CAG GGC AGG TGG AAG GTG CGC AAG TCA 288 Ser Asp Ser Ser He Arg Val Gin Gly Arg Trp Lys Val Arg Lys Ser 85 90 95 TTC TTC AAA CTA CAG GGC TCC TTT GAT GTC AGT GTC AAG GGC ATC AGC 336 Phe Phe Lys Leu Gin Gly Ser Phe Asp Val Ser Val Lys Gly He Ser 100 105 110 ATT TCG GTC AAC CTC CTG TTG GGC AGC GAG TCC TCC GGG AGG CCC ACA 384 He Ser Val Asn Leu Leu Leu Gly Ser Glu Ser Ser Gly Arg Pro Thr 115 120 125 GTT ACT GCC TCC AGC TGC AGC AGT GAC ATC GCT GAC GTG GAG GTG GAC 432 Val Thr Ala Ser Ser Cys Ser Ser Asp He Ala Asp Val Glu Val Asp 130 135 140 ATG TCG GGA GAC TTG GGG TGG CTC TTG AAC CTC TTC CAC AAC CAG ATT 480 Met Ser Gly Asp Leu Gly Trp Leu Leu Asn Leu Phe His Asn Gin He

Claims: -30- 145 150 155 160 GAG TCC AAG TTC CAG AAA GTA CTG GAG AGC AGG ATT TGC GAA ATG ATC 528 Glu Ser Lys Phe Gin Lys Val Leu Glu Ser Arg He Cys Glu Met He 165 170 175 CAG AAA TCA GTG TCC TCC GAT CTA CAG CCT TAT CTC CAA ACT CTG CCA 576 Gin Lys Ser Val Ser Ser Asp Leu Gin Pro Tyr Leu Gin Thr Leu Pro 180 185 190 GTT ACA ACA GAG ATT 591 Val Thr Thr Glu He 195 (2) INFORMATION FOR SEQ ID NO:4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 197 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein Cxi) SEQUENCE DESCRIPTION: SEQ ID NO: : Ala Asn Pro Gly Leu Val Ala Arg He Thr Asp Lys Gly Leu Gin Tyr 1 5 10 15 Ala Ala Gin Glu Gly Leu Leu Ala Leu Gin Ser Glu Leu Leu Arg He 20 25 30 Thr Leu Pro Asp Phe Thr Gly Asp Leu Arg He Pro His Val Gly Arg 35 40 45 Gly Arg Tyr Glu Phe His Ser Leu Asn He His Ser Cys Glu Leu Leu 50 55 60 Hie Ser Ala Leu Arg Pro Val Pro Gly Gin Gly Leu Ser Leu Ser He 65 70 75 80 Ser Asp Ser Ser He Arg Val Gin Gly Arg Trp Lys Val Arg Lys Ser 85 90 95 Phe Phe Lys Leu Gin Gly Ser Phe Asp Val Ser Val Lys Gly He Ser 100 105 110 He Ser Val Asn Leu Leu Leu Gly Ser Glu Ser Ser Gly Arg Pro Thr 115 120 125 Val Thr Ala Ser Ser Cys Ser Ser Asp He Ala Asp Val Glu Val Asp 130 135 140 -31- Met Ser Gly Asp Leu Gly Trp Leu Leu Asn Leu Phe His Asn Gin He 145 150 155 160 Glu Ser Lys Phe Gin Lys Val Leu Glu Ser Arg He Cys Glu Met He 165 170 175 Gin Lys Ser Val Ser Ser Asp Leu Gin Pro Tyr Leu Gin Thr Leu Arg 180 185 190 Val Thr Thr Glu He 195

Inventors: GRINNA LYNN S, GRINNA, LYNN, S.
Applicants: XOMA CORP, XOMA CORPORATION
Application year: 1993
Main classification: C12N15
IPC codes: C07K1, C07K14, C07K19, C12N5, C12N15, C12P21, C12R1