Production of proteins in active forms

Abstract: A method for the preparation of a protein in a physiologically active or native form comprises providing a source of protein in a solubilized form and an agent capable of rupturing atomic forces within the molecule, and contacting the protein with the rupturing agent in water in an amount sufficient to allow the protein to convert to a physiologically active form. The rupturing agent is selected from urea, or derivatives thereof, dimethysulphone, and mixtures thereof.

Description: The present invention relates to a method for the preparation of a protein in a biologically active or native form. Recombinant DNA technology provides potentially extremely valuable means of synthesizing amounts of desirable eukaryotic (usually mammalian) proteins such as hormones, interferons, and enzymes. Although it has been proved to be relatively easy to manipulate organisms such as bacteria in order to produce the desired protein, the host organism does not normally secrete the protein product into the culture medium. Thus lysis of the organisms (for example bacteria), followed by isolation of the desired protein is usually necessary. A protein is a chain of amino acids linked by peptide bonds. In the normal biologically active form of such a protein or its native form as it is referred to, the chain is folded into a thermodynamically preferred three dimensional structure, the conformation of which is maintained by steric interaction and weak interactions such as hydrogen bonding, hydrophobic interactions and charge interactions. In the prior art, the usual aggregation and insolubility under folding conditions of fully, or partially, unfolded proteins requires that folding be carried out in very dilute solutions, consequently in large volumes. The handling of such dilute solutions and large volumes together with toxic reducing agents such as B-mercaptoethanol would add significantly to the cost when such processes are applied industrially. In copending EP-A-226,448 applicants have described a method for the recovery of proteins in a soluble form from an insoluble protein source utilising a cationic surfactant. Whilst this process allows for the efficient recovery of proteins in a soluble form, the proteins may not exhibit their normal biological activity. The proteins so recovered may not be in their native form. EP-A-114,506 describes a method for recovering, in active form, proteins which have been produced in host cells, which are heterologous thereto, and which are at least partially deposited inside the cells as clumps of insoluble protein. The method employs a strong denaturant such as a combination of guanidine and urea with mercaptoethanol to solubilize the protein. Solubilized proteins are then renatured in a weaker concentration of denaturing agent. GB-A-2,001,326 describes a process for the isolation of glycoproteins from paramyxovirus by treating the virus with a cationic detergent to selectively solubilize the glycoprotein components. The glycoprotein components are separated from residual intact sub-viral particles using conventional methods, and may then be used in vaccines. In Analytical Biochemistry, no. 109, 1980, pages 207-215 (Academic Press. Inc.) A.J. Furth describes methods for removing unbound detergent from hydrophobic proteins and teaches that the choice of method may be governed largely by the properties of the detergent. Amongst the methods described are phage partition methods, affinity chromatography, ion-exchange chromatography, gel chromatography, sucrose density centrifugation and dialysis. EP-A-212,960 (which was published after the priority date of the present application, and therefore falls within the terms of article 54(3) of the European Patent Convention) describes the purification and reactivation of proteins after solubilization with sodium dodecyl sulphate (SDS). The solution thus obtained is treated with urea and the protein is purified by anion exchange chromatography. The protein solution obtained from the anion exchange column is dialyzed to remove the urea, allowing the protein to refold into its native confirmation. Biochemistry 24,7662-68 (1985) Brems et al is concerned with guanidine hydrochloride induced denaturation of bovine growth hormone. They demonstrate that the denaturation transitions were completely reversible within the transition zone (2.0-6.0 M guanidine hydrochloride). Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties related to the prior art. According to the invention there is provided a method for the preparation of a protein in a biologically active form including: (a) solubilizing a water-insoluble protein, obtained from inclusion bodies, with an aqueous cationic surfactant to form a protein solution, said protein being selected from the group consisting of physiologically active polypeptides, growth hormones, interferons, immunogens and lymphokines; and (b) contacting the protein solution with an aqueous mixture of a weak denaturing agent selected from the group consisting of urea, dimethylsulphone and mixtures thereof in an amount sufficient to maintain the protein in solution during removal of residual cationic detergent, thereby allowing the protein in the solution to maintain its biologically active form. The cationic surfactant may be as described in EP-A-226.448. The solubilized protein may accordingly be provided from a source of insoluble protein including protein aggregates. In a preferred embodiment of the invention the method further includes exchanging the solvent of the protein solution of step (a) for a biologically acceptable solvent or diluting the protein solution of step (a) with a biologically acceptable solvent, said biologically acceptable solvent being selected from the group consisting of water, dilute aqueous solutions and buffer, to form a protein solution in which the protein refolds to its biologically active form, which is of substantially reduced surfactant concentration when compared with the solvent of the protein solution of step (a) and which is the protein solution which is used in step (b). It is particularly preferred that the solubilised protein is contacted with said weak denaturing agent in a solution free from reducing agents. The present invention is particularly applicable to biologically active proteins synthesised by microorganisms and eukaryotic cell lines which have been modified by recombinant DNA technology. The protein aggregate may comprise an inclusion body isolated by disruption or lysis of a host cell which may have been transformed or transfected with a vector including a gene coding for the protein. However it is not restricted thereto. In addition the present invention is applicable to naturally occurring precipitated protein complexes. The protein aggregates which may be recovered according to the present invention may be selected from protein precipitates including inclusion bodies and cytoplasmic aggregates. The inclusion bodies may be selected from biologically active polypeptides and peptides including growth hormones including porcine, bovine and ovine growth hormones, interferons, immunogens and lymphokines. In particular, it has surprisingly been discovered that the solubilised protein aggregates may comprise a solution of crude inclusion bodies which, after solubilisation, have been subjected to little or no purification prior to their utilisation in the process of the present invention. For example, crude inclusion bodies including growth hormones in concentrations as low as approximately 13% may successfully be processed utilising the process of the present invention. The weak denaturing agent may be an agent capable of rupturing hydrogen bonds, hydrophobic interactions or charge interactions, and is preferably selected to be sufficiently mild to allow other appropriate atomic forces to reform. The agent, which is selected from the group consisting of urea, derivatives thereof including dimethylhydroxy urea, and dimethylsulphone and mixtures thereof, may be provided in a suitable aqueous solution including a polar organic solvent. Acetonitrile, acetic acid or dimethylsulphone may be used. The protein in solubilised form may be contacted with the aqueous mixture of a weak denaturing agent in any suitable manner. For example, the protein in solubilised form may be dialysed or exchanged into a solution of the weak denaturing agent. The protein may be utilised in a concentrated form, and may be present in an amount of approximately 1 to 200 mg/ml. In the preferred embodiment in which the biologically active protein is contacted with a biologically acceptable solvent, the physiologically acceptable solvent may be water or other dilute aqueous solution, although a buffered aqueous solution is preferred. It has been found, surprisingly, that, after the treatment according to the present invention, the protein is rendered soluble in aqueous solution and is converted into its biologically active form. Preferably, the pH of the solution is optimised to ensure solubility of the protein and stability of the solution. For example when the biologically active protein is a growth hormone, the pH is maintained between approximately 8.5 and 11.0. The weak denaturing agent may be utilised in any suitable amount. We have surprisingly found that relatively low concentrations of the weak denaturing agent are effective in the method according to the present invention. The weak denaturing agent may be used in concentrations of from approximately 0.5M to 8M, preferably between approximately 3M and 5M. The method may be conducted at any suitable temperature above the freezing point of the solution. Preferably a temperature in the range of approximately 4 to 25°C, more preferably 4 to 10°C, may be used. At such relatively low temperatures an improved yield may be achieved. Furthermore, in contrast to the prior art, we have surprisingly found that, in the method for the preparation of protein in a biologically active form according to the present invention, the solubilised protein may be contacted with the weak denaturing agent in solutions free or substantially free from reducing agents. More surprisingly, we have found that the amount of reducing agent may be substantially reduced or omitted also from the solubilisation step. For example, in examples 1 and 2 below the amount of dithiothreitol in the solubilisation step and the amount of mercaptoethanol in the subsequent contact step may be reduced or eliminated. Where the recovery of proteins in solubilised form utilises a surfactant as described in EP-A-226,448, it is preferred that the solubilised protein be separated from the resulting solution. The purification step may be selected from differential elution of the solubilised protein through a chromatographic support, dialysis, ultrafiltration, differential precipitation, or ligand specific isolation. Whilst such a separation step may be used in conjunction with the method according to the present invention it has surprisingly been found that such a separation step is not required to produce a physiologically active preparation. The present invention will now be more fully described with reference to the accompanying examples. It should be understood, however, that the description following is illustrative only and should not be taken in any way as a restriction on the generality of the invention described above. EXAMPLE 1 Size Exclusion Chromatography An experiment was conducted with crude inclusion bodies obtained from transformed E.coli cells. The inclusion bodies, containing 1-190AA methionine-porcine growth hormone, derived from plasmid, pMG935, were isolated, after cell disruption, by centrifugation. The insoluble pellet (100 g wet weight) was washed three times with an aqueous solution containing 5% Triton X-100 and 5mM EDTA and then three times with water containing 5mM EDTA. The pellet was recovered at each step by centrifugation (25,000g). The final pellet was resuspended and vigorously agitated with an aqueous solution of cetyltrimethylammonium bromide (100ml of 18.5% w/v), 0.15M TRIZMA (pH 9.0), 50mM EDTA and dithiothreitol (5% w/v). After 1 hour the mixture was centrifuged (25,000g, 30 min.), the clear supernatant retained and the pellet resuspended in 100 ml of the fresh solubilising buffer. Following collection of the final supernatant the pellet was discarded and the combined supernatant loaded onto a column (75 cm x 11 cm) packed with Sephacryl S300 which had previously been equilibrated with eluant consisting of a solution of cetyltrimethylammonium bromide (0.36%), 30mM TRIZMA (pH 10.0) and dithiothreitol (0.5% w/v). Elution of the column followed at a flow rate of 11 ml/min. After collection of some 8L of eluant the fraction containing the growth hormone was isolated in some 600 ml of eluant. This fraction was then diluted approximately 1:10 with water to give a UV (280 nm) absorbance of 1.5, and the solution placed into cellulose dialysis sacks (Union Carbide type 30), and placed into exchange buffer containing 5M urea, 0.05M glycine (pH 11.0) and B-mercaptoethanol (0.1%) sufficient to provide an estimated 1:160,000 dilution of the initial solubilising buffer contained within the dialysis sack. The dialysis sacks were then placed into a physiologically compatible exchange buffer consisting of mannitol (1% w/v), 0.05M glycine (pH 10.0) without exclusion of air at room temperature. The buffer was exchanged at 8 hourly intervals with fresh buffer sufficient to provide a 1:160,000 dilution of the urea solution. This final product was then tested for biological activity in rats according to the rat tibia assay, and was found to be active compared to a positive control containing native porcine growth hormone extracted from fresh pituitaries (see Table 1). EXAMPLE 2 Experiments paralleling those described in Example 1 were conducted with inclusion bodies containing 4-190AA porcine growth hormone derived from plasmid pMG 936 in E . coli . The experiment used inclusion bodies containing 4-190AA porcine growth hormone (100g wet wt) isolated in the same manner as that described for 1-190AA methionine porcine growth hormone inclusion bodies. The inclusion body paste was vigorously agitated with an aqueous solution with cethyltrimethylammonium chloride (200 ml of 18.5% w/v, 25°C) 0.15M TRIZMA (pH 10.0), 50 mM EDTA and dithiothrietol (3% w/v). After 1 hr the mixture was diluted with water (80ml) and clarified by filtration through a pad of diatomaceous earth. The clear filtrate was loaded onto a column (75cm x 11cm) packed with Sephacryl S300 which had previously been equilibrated with eluant consisting of an aqueous solution of cetyltrimethylammonium chloride (0.35% w.v), 30mM TRIZMA (pH 10.0) and dithiothreitol (0.5% w/v). Elution of the column followed at a mean flow rate of 11 ml/min. After collection of some 10L of eluant the fraction containing the growth hormone was isolated in some 800 ml of eluant. The fraction after dilution with eluant buffer, approximately 1:10, gave a UV (280nm) absorbance of 0.8. The fraction was placed into cellulose dialysis sacks and exchanged into 1,3 bis (hydroxymethyl) urea (3.5M) , 0.05M glycine (pH 11.0) sufficient to provide a 1:160,000 dilution of microsolutes contained within the sacks. The dialysis sacks were then placed into physiologically compatible exchange buffer consisting of mannitol (1% w/v), 0.05M TRIZMA (pH 10.0) without exclusion of air at 5°C. The buffer was exchanged at 8 hourly intervals with fresh buffer, sufficient to provide a 1:160,000 dilution of microslutes in the sacks. This final product was found to be active when tested for biological activity in rats in a similar manner to that described in Example 1. EXAMPLE 3 a) In the Presence of Reducing Agent The fraction (600 ml) containing growth hormone isolated by size exclusion chromatography, as described above in Example 1, was placed directly into an Amicon CH2A concentrator equipped with a S1 Y10 cartridge and the solution continuously exchanged by dialysis with a fresh buffer containing 5M urea, 0.05M glycine (pH 11.0) and 0.1% B-mercaptoethanol. Sufficient exchange buffer was used to provide a 1:160,000 dilution of the initial microsolutes. The resulting solution was subsequently exchanged in a similar manner into a physiologically compatible aqueous buffer containing mannitol (1%) and 0.05M glycine (pH 10.0) without exclusion of air at room temperature. This final product was found to be active compared to a positive control containing native porcine growth hormone according to the rat tibia assay (see Table 1). b) In the Absence of Reducing Agent The fraction (600 ml) containing growth hormone isolated by size exclusion chromatography, as described above in Example 1, was placed directly into an Amicon CH2A concentrator equipped with a S1 Y10 cartridge and the solution continuously exchanged by dialysis with a fresh buffer consisting only of 5M urea, 0.05M glycine (pH 11.0). The urea solution was then similarly exchanged into an aqueous solution of mannitol (1%), (w/v) and 0.05M glycine (pH 10.0). In both dialysis steps sufficient exchange buffer was used to provide a 1:160,000 dilution of the microsolutes. The final product was found to be highly soluble in physiologically acceptable buffer and shown to be biologically active by the rat tibia assay (see Table 1). EXAMPLE 4 Crude Inclusion Bodies Another experiment was conducted beginning with crude inclusion bodies (50mg) containing 4-190AA synthetic porcine growth hormone, previously washed three times with an aqueous solution containing 5% Triton X-100 and 5mM EDTA and then three times with an aqueous 5mM EDTA. The inclusion bodies were vigorously agitated with an aqueous solution of cetyltrimethylammonium bromide (1ml of 10.5% w/v), 0.15M TRIZMA (pH 10.0) 50mM EDTA and dithiothreitol (5% w/v). After 1 hour the mixture was centrifuged (25,000 G, 30 min). The clear supernatant was then diluted with approximately 1:50 with water to give a UV (280nm) absorbance of 1.5 and the clarified solution placed into dialysis sacks (Union Carbide Type 30) and dialysed against exchange buffer containing 7M urea, 0.05M glycine (pH 11.0); sufficient exchange buffer was used to provide a dilution of 1:160,000 of initial microsolutes. The dialysis sacks containing 7M urea were then placed into a physiologically acceptable exchange buffer consisting of 0.05M glycine (pH 10.0), without exclusion of air at room temperature, and the process of dialysis continued until a dilution of 1:160,000 of initial microsolutes was achieved. The final solution was then found to have biological activity when compared to a positive control comprising a preparation of native porcine growth hormone extracted from fresh pituitaries (see Table 1). EXAMPLE 5 An experiment was conducted with crude inclusion bodies (50mg) containing the D1 fragment of the 32kDa structural protein from infectious bursal disease virus which had previously been sequentially washed (x3) with aqueous Triton X-100 (5%), 5mM EDTA and aqueous 5mM EDTA. The inclusion bodies were vigorously agitated with an aqueous solution containing a mixture of cetyltrimethylammonium bromide (0.5 ml of 18.5% w/v) and cetylpyridinium chloride monohydrate (0.5m. of 12% w/v), 0.15M TRIZMA (pH 10.0), 50mM EDTA and dithiothreitol (5% w/v). After 1 hour the mixture was centrifuged (25,000 g 30 min.). The clear supernatant was then diluted approximately 1:30 with 5M urea and the solution placed into dialysis sacks and dialysed against exchange buffer containing 5M urea, 0.05M glycine (pH 11.0), sufficient exchange buffer was used to provide a dilution of approximately 1:160,000 of initial microsolutes. The dialysis sacks were then placed into a physiologically acceptable exchange buffer consisting of mannitol (1% w/v), 0.05M TRIZMA (pH 10.0) without the exclusion of air at room temperature. The process of dialysis was continued until a dilution of approximately 1:160,000 of initial microsolutes was achieved. An immuno-dot blot analysis of the final solution using nitro-cellulose paper and a monoclonal antibody to the D1 polypeptide confirmed the antigenicity of the fused polypeptide. EXAMPLE 6 An experiment was conducted with washed inclusion bodies containing 1-190AA methionine-porcine growth hormone. The inclusion bodies (50mg) were vigorously aggitated (1hr) with a solution of acetonitrile (0.2ml), aqueous buffer (0.1M glycine, pH 8.5; 0.8ml) and aqueous cetyltrimethylammonium bromide (0.5 ml of 30% w/v) and dithiotreitol (3% w/v) in a test tube at 25°C. The mixture was then centrifuged (25,000g, 20 min.) to give a clear supernatant. The supernatant was then diluted approximately 1:3 with a 1:1 mixture of 2M urea and 2M dimethylsulphone and placed into dialysis sacks. The mixture was dialysed against a solution of 2M urea and 2M dimethylsulphone (1:1) until a dilution of initial microsolutes of 1:160,000 had been achieved. The dialysis sacks were then placed into a physiologically compatible buffer consisting of aqueous 0.05M TRIZMA (pH 10.0) and NaCl (0.8%) without the exclusion of air and dialysis was continued to give a dilution of microslutes of 1:160,000. A test for biological activity of the final solution by the rat tibia assay proved positive when compared to a positive control containing naturally derived porcine growth hormone. EXAMPLE 7 An experiment was conducted with washed inclusion bodies containing 1-190AA methionine-porcine growth hormone. The inclusion bodies (50mg wet wt) were vigorously aggitated (1hr) with a solution of cetyltrimethylammonium bromide (1.0 ml of 18.5% w.v), 0.15M TRIZMA (pH 10.0) and 50mM EDTA. After 1hr the mixture was centrifuged (25,000g, 30 min). The clear supernatant was then diluted approximately 1:50 with water to give a UV (280 nm) absorbance of 1.2 and the clarified solution placed into dialysis sacks (Union Carbide Type 30) and the solution exchanged against 7M urea, 0.05M glycine (pH 11.0), sufficient to provide a dilution of microsolutes by approximately 1:160,000. The dialysis sacks were then placed into a physiologically acceptable buffer consisting of 0.05M TRIZMA (pH 9.5) at 4°C without the exclusion of air and the process of dialysis continued until a dilution of approximately 1:160,000 of initial microsolutes was achieved. The final solution was then found to have biological activity when compared to a positive control (see Table 1).

Claims: A method for the preparation of a protein in a biologically active form including: (a) solubilizing a water-insoluble protein, obtained from inclusion bodies, with an aqueous cationic surfactant to form a protein solution, said protein being selected from the group consisting of physiologically active polypeptides, growth hormones, interferons, immunogens and lymphokines; and (b) contacting the protein solution with an aqueous mixture of a weak denaturing agent selected from the group consisting of urea, dimethylsulphone and mixtures thereof in an amount sufficient to maintain the protein in solution during removal of residual cationic detergent, thereby allowing the protein in the solution to maintain its biologically active form. A method according to claim 1 further including exchanging the solvent of the protein solution of step (a) for a biologically acceptable solvent or diluting the protein solution of step (a) with a biologically acceptable solvent, said biologically acceptable solvent being selected from the group consisting of water, dilute aqueous solutions and buffer, to form a protein solution in which the protein refolds to its biologically active form, which is of substantially reduced surfactant concentration when compared with the solvent of the protein solution of step (a) and which is the protein solution which is used in step (b). A method according to claim 1 or 2 wherein the solubilized protein is contacted with said weak denaturing agent in a solution free from reducing agents. A method according to any preceding claim wherein said inclusion bodies are crude inclusion bodies. A method according to any preceding claim wherein said weak denaturing agent is present in concentrations of from approximately 0.5 M to 8 M. A method according to any preceding claim wherein the pH of the solution so formed is optimized to ensure solubility of the protein. A method according to any preceding claim wherein, when said biologically active protein is a growth hormone, the pH is maintained between approximately 8.5 and 11.0.

Inventors: PATRONI JOSEPH JOHN, PATRONI, JOSEPH JOHN
Applicants: SOUTHERN CROSS BIOTECH PTY LTD, SOUTHERN CROSS BIOTECH PTY.LTD.
Application year: 1988
Main classification: C07K3
IPC codes: C07K14, C07K1, C07K19