Production of proteins in active forms

Abstract: For the preparation of a protein in a physiologically active or native form, a source of protein in a solubilised form is contacted with cationic exchange medium which may be a cationic exchange resin which generates a rapid ion exchange rate. The cationic exchange resin may be provided in the form of a cationic exchange chromatography column, the source of protein being contacted therewith via elution of the chromatography column. The protein is then recovered in a physiologically active form. This represents a highly efficient, and hence cost effective, method for the recovery of proteins.

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 proved to be relatively easy to manipulate organisms such as bacteria to produce the desired protein, the host organism does not normally secrete the over-produced 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 exists as 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 commonly referred to, the chain is folded into a thermodynamically preferred three dimensional structure, the conformation of which may be maintained by steric interaction intermolecular and intramolecular forces 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 the presence of denaturants, and 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 adds significantly to the cost when such processes are applied industrially. In EP-A-226,448 applicants have described a highly economical 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. GB-A-2,001,326 describes a process for the isolation of glycoproteins from paramyzovirus 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. EP-A-218,374 describes the purification and reactivation of proteins after solubilisation with sodium dodecyl sulphate (SDS). The solution thus obtained is dialysed or refrigerated to remove a portion of the SDS, and then subjected to ion-retardation chromatography to remove the remaining SDS. The protein solution thus obtained is subjected to anion-exchange chromatography. EP-A-212,960 describes the purification and reactivation of proteins after solubilisation 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. 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 soluble and physiologically active form from which organic cations have been removed, comprising: providing a protein, selected from the group consisting of growth hormones, interferons, immunogens and lymphokines, in a solubilized form, wherein the protein in the solubilized form is obtained by treating insoluble protein aggregates with an aqueous cationic surfactant, and wherein said cationic surfactant includes an organic cation selected from the group consisting of cetyl trimethylammonium cations, cetyl pyridinium cations, tetradecyl trimethylammonium cations, dodecyl trimethylammonium cations, mixed n-alkyl dimethyl benzyl ammonium cations, N. N-dimethyl-N-(2-(2-(4-(1.1.3.3.-tetramethylbutyl) - phenoxyl)ethoxy) ethyl)benzenemethanaminium cations; contacting said solubilized protein with a nuclear sulfonic acid cationic exchange resin, wherein the counter ion of said cationic exchange resin is an alkali metal; and recovering the protein in a soluble and physiologically active form from which organic cations have been removed. The nuclear sulfonic acid cationic exchange resin may be of any suitable type which generates a rapid ion exchange rate. For example the ion exchange process may be completed within several hours rather than days. Accordingly, a high porosity, high capacity resin is preferred. After equilibration, a nuclear sulfonic acid cationic exchange resin of the macroporous type sold under the trade designation "Dowex" and available from The Dow Chemical Company has been found to be suitable. The cationic exchange resin may be selected from the group consisting of DOWEX 50W-H, DOWEX 50x4, and DOWEX 50Wx1 exchange resins. A cation exchange resin sold under the trade designation "Duolite C20" from Rohm and Haas has also been found to be suitable. A particular advantage of the use of a cationic exchange medium in the method according to the present invention is the ability to regenerate the medium as required. The cationic exchange resin may be provided in the form of a cationic exchange chromatography column, and wherein the protein is contacted therewith by elution of the chromatography column with a mixture of the protein and a physiologically acceptable solvent. Whilst the mechanism of renaturation is complex, in part, the treatment with the appropriate cationic exchange media removes organic cations present or formed during the solubilisation and substitutes therefor other cations, the protein product of which is rapidly produced as a solution in a physiologically acceptable solvent and is in a physiologically active form. It will be understood that, in its preferred aspect, the method according to the present invention provides a mechanism for the recovery of proteins via a single recovery step, once the proteins have been solubilised. This represents a significant improvement in efficiency, and thus cost, since steps such as dialysis or chemical refolding treatments may thus be avoided. The pH at which the method according to the present invention is conducted may be varied depending on the optimum solubility characteristics of the protein selected. The pH may also be selected from about pH 2.5 to about pH 12.5. The protein in a solubilised form may be provided by the treatment of the insoluble form with an aqueous cationic surfactant and/or polar organic solvent as described in EP-A-226,448. The solubilized protein may be provided from a source of insoluble protein including protein aggregates. The present invention is particulary 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 method according to the present invention is also applicable to the process described in EP-A-279,619 for preparation of a protein in a biologically active form by solubilizing the protein, derived from inclusion bodies, with an aqueous cationic surfactant, and converting the protein to a biologically active form in a physiologically acceptable solution, such as water, a dilute aqueous solution or buffer. The protein aggregates which may be recovered according to present invention may be selected from inclusion bodies and cytoplasmic aggregates. The inclusion bodies may be selected from biologically active polypeptides and peptides including growth hormones such as porcine, ovine and bovine growth hormones, interferons, immunogens and lymphokines, or synthesised heterogeneous or homogeneous polymers thereof. The recovery step according to the present invention may include treating the product of the cation exchange resin treatment step to recover the protein. The treatment step may include a filtration step. In the preferred form, where the cationic exchange medium is in the form of a cationic exchange chromatography column, it will be understood that the cation exchange resin treatment and recovery steps may be combined. The protein in a solubilised form may be contacted with the cationic exchange resin in any suitable concentrated form. The protein may be provided in a concentration of approximately 1 to 200 mg/ml, preferably approximately 90 to 150 mg/ml. Preferably the method further comprises mixing the product of the cation exchange resin treatment step with a physiologically acceptable solvent selected from the group consisting of water and dilute aqueous buffer solutions, wherein the product of the cation exchange resin treatment step is rendered soluble in the physiologically acceptable solvent; and separating the protein from the resulting solution after removing the organic cations from the solution. In the method for the recovery of proteins in a solubilised form, utilising a cationic surfactant as described in EP-A-226,448 it is preferred that the solubilised protein be separated from the resulting solution. Preferably the separating step is accomplished by differential elution of the solubilized proteins through a chromatographic column, dialysis, ultrafiltration or differential precipitation, and the eluant or liquid medium is water or other dilute aqueous buffers. Whilst such a separation step may be used in conjunction with the method according to the present invention, in contradistinction to the prior art the present invention substantially simplifies this step as it may be conducted after the crude protein is converted into a physiologically active form, and the eluant or liquid medium used may be water or other dilute aqueous dilution e.g. an aqueous buffer. 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 40°C more preferably 4 to 10°C may be used. A pharmaceutical composition including a protein in a physiologically active or native form may be prepared by the above method. The pharmaceutical composition may further include a physiologically acceptable carrier or recipient. The carrier or recipient may be a solvent. The pharmaceutical composition may be a veterinary composition. In the present invention it will be understood that in a preferred aspect the protein is produced in a physiologically active or native form and in a physiologically acceptable soluent. 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 Crude inclusion bodies (600g wet weight) containing methionyl 1-190AA porcine growth hormone were isolated by conventional disruption of modified E.coli . The inclusion bodies were washed three times with a solution of 5% Triton X-100 and 5mM EDTA, and finally three times with aqueous 5nM EDTA: Vigorous agitation of the washed inclusion bodies in the presence of a solution of cetyl trimethylammonium bromide (500ml of 18.5% w/v), 0.15M TRIZMA (pH 10.0), 50mM EDTA and dithiothreitol (5% w/v) resulted in complete solubilisation of the insoluble growth hormone. During the solubilisation the pH of this solution was kept constant (pH 10.0) by addition of some 1M sodium hydroxide. The mixture was then clarified by centrifugation (25,000g, 30min), and the clear, pale yellow supernatant diluted (1:10) with water. The solution was then poured onto neutral Dowex 50W x 1; 100 micron mesh (beads) (sodium form) ion exchange resin, and the mixture placed into a roller bottle (2L, 15°). The liquid was then isolated by filtration, and was found to contain the growth hormone after substantially complete recovery. The soluble preparation containing significant quantities of cellular proteins as impurities was shown to be biologically active in the rat tibia bioassay (Table 1). EXAMPLE 2 The method of Example 1 was repeated in the absence of reducing agent. Reducing agents are preferably avoided due to their toxicity and volatility. An experiment was conducted wherein washed inclusion bodies (100g, wet weight) containing methionyl 1-190AA porcine growth hormone were vigorously agitated (2L) in the presence of cetyltrimethylammonium chloride (200ml, of 200% w/v), 0.15M TRIZMA (pH 10.0) and 40mM EDTA. The pH of the solution was kept constant throughout solubilisation. The mixture was then immediately clarified by centrifugation (25,000g, 30 min), and the clear supernatant diluted 1:10 with water. The solution was then poured onto neutral, moist Dowex 50W x 4; 50-100 micron mesh (beads) (regenerated sodium form) ion exchange resin (400ml), the mixture placed into a conical flask and agitated (2L, 25°). The liquid was then isolated by decantation and was found to contain the growth hormone in a soluble form. The soluble preparation contained significant quantities of other proteins as impurities but was shown to be biologically active in the rat tibia bioassay (Table 1). EXAMPLE 3 Crude inclusion bodies (600g wet weight) containing methionyl 1-190AA porcine growth hormone was isolated and washed as described in Example 1. The inclusion bodies were then thoroughly agitated with cetyltrimethylammonium chloride (500ml of 18.5% w/v), 0.15M TRIZMA (pH 10.0), 50mM EDTA and dithiothreitol (3% w.v) resulted in complete solubilisation of the insoluble growth hormone. During the solubilisation the pH of the solution was maintained constant (pH 10.0) by addition of some 1M sodium hydroxide. The mixture was then clarified by centrifugation (25,000g, 30 min.), and the clear, supernatant diluted (1:4) with 5M Urea 0.05M glycine (pH 11.0). The solution was immediately poured onto preequilibrated neutral Dowex 50W x 1; 100 micron mesh (beads) (sodium form), ion exchange resin (1.5L) and the mixture placed into a roller bottle (2L, 20°). The liquid was then isolated by filtration and subjected to dialysis with 0.05M TRIZMA (pH 10.0, 1hr, 4°) in an Amicon Ch2H concentrator equipped with an S10 Y3 spiral wound cartridge. The solution containing the growth hormone was then allowed to stand at 4° for 16h prior to loading on a preequilibrated anion exchange chromatography support (Whotman DE 52). Chromatography then produced by elution at 60 ml/min with a solution of 0.05 TRIZMA pH 9.8 and an increasing sodium chloride gradient to a final 0.07M. Fractions containing pure growth hormone were then isolated and pooled. This purified growth hormone was found to be biologically active in a rat tibia bioassay (Table 1). EXAMPLE 4 An experiment was conducted with 4-190AA porcine growth hormone substantially as indicated in Example 1. Again the final solution as obtained by filtration after contact with the resin was shown to be biologically active in the rat tibia bioassay (Table 1). EXAMPLE 5 An experiment was conducted where the final solution obtained after contact with the cation exchange resin as described in Example 1 above, was directly applied to an ion exchange column (DEAE Fast Flow 11cm + 30cm) at pH 11.0, and pure growth hormone was obtained after elution of the column with increasing ionic strength. This purified growth hormone was found to be biologically active in a rat tibia bioassay (Table 1). EXAMPLE 6 An experiment was conducted with crude inclusion bodies (50mg) containing the D1 fragment of the 32kDa structural protein from infectious bursal disease virus which were sequentially washed (x3) with aqueous Triton X-100 (5%), 5mM EDTA and aqueous EDTA. The inclusion bodies were vigorously agitated with an aqueous solution containing a mixture of cetyltrimethylammonium bromide (0.5ml of 18.5% w/v) and cetylpyridinium chloride monohydrate (0.5ml of 12% w/v), 0.15M TRIZMA (pH 10.0), 50mM EDTA and dithiothreitol (5% w/v). After 1 hour the mixture was centrifuged (25,000g, 30min). The clear supernatant was then diluted 1:4 with 5M urea, 0.05M glycine (pH 11.0) and the solution poured onto pre-equilibrated Dowex 50W x 1; 100 micron mesh (beads) (sodium form) ion exchange resin (10ml) and the mixture placed into a roller bottle (1h, 25°). The liquid was then isolated by filtration. An immuno-dot blot analysis of the final physiologically acceptable solution using nitro-cellulose paper and a monoclonal antibody to the D1 polypeptide confirmed the antigenicity of the fused polypeptide. The biological* activity of preparations described above as assessed by the rat tibia assay, relative to an equivalent dose of porcine growth hormone isolated from fresh pituitaries as positive control (assessed as 100 ± 10%) Treatment Group Biological* Activity (%) Example 1 27 Example 2 24 Example 3 94 Example 4 30 Example 5 90

Claims: A method for the preparation of a protein in a soluble and physiologically active form from which organic cations have been removed, comprising: providing a protein, selected from the group consisting of growth hormones, interferons, immunogens and lymphokines, in a solubilized form, wherein the protein in the solubilized form is obtained by treating insoluble protein aggregates with an aqueous cationic surfactant, and wherein said cationic surfactant includes an organic cation selected from the group consisting of cetyl trimethylammonium cations, cetyl pyridinium cations, tetradecyl trimethylammonium cations, dodecyl trimethylammonium cations, mixed n-alkyl dimethyl benzyl ammonium cations, N. N-dimethyl-N-(2-(2-(4-(1.1.3.3.-tetramethylbutyl) - phenoxyl)ethoxy) ethyl)benzenemethanaminium cations; contacting said solubilized protein with a nuclear sulfonic acid cationic exchange resin, wherein the counter ion of said cationic exchange resin is an alkali metal; and recovering the protein in a soluble and physiologically active form from which organic cations have been removed. The method of claim 1 wherein the cationic exchange resin is selected from the group consisting of DOWEX 50W-H, DOWEX 50x4, and DOWEX 50Wx1 exchange resins. A method as claimed in Claim 2 wherein the cationic exchange resin is provided in the form of a cationic exchange chromatography column, and wherein the protein is contacted therewith by elution of the chromatography column with a mixture of the protein and a physiologically acceptable solvent. A method as claimed in any preceding claim wherein the protein is provided in a concentration of approximately 1 to 200 mg/ml. A method as claimed in any preceding claim further comprising: mixing the product of the contacting step with a physiologically acceptable solvent selected from the group consisting of water and dilute aqueous buffer solutions, wherein the product of the contacting step is rendered soluble in the physiologically acceptable solvent; and separating the protein from the resulting solution after removing the organic cations from the solution. A method as claimed in claim 5 wherein the separating step is accomplished by differential elution of the solubilized proteins through a chromatographic column, dialysis, ultrafiltration or differential precipitation, and wherein the eluant or liquid medium is water or other dilute aqueous buffers.

Inventors: BRANDON MALCOLM ROY, PATRONI JOSEPH JOHN, BRANDON, MALCOLM ROY, PATRONI, JOSEPH JOHN
Applicants: SOUTHERN CROSS BIOTECH PTY LTD, SOUTHERN CROSS BIOTECH PTY.LTD.
Application year: 1988
Main classification: C07K1
IPC codes: C12P21, C07K14, C07K1