Patent ID: 7306931

Claim:
A method for preparing a refolded, soluble form of an insoluble or aggregated protein that is a member of the Growth Hormone supergene family and which contains one or more added free cysteine residues, comprising the following steps, in order, of: a) causing a host cell to express a protein containing one or more added free cysteine residues that is a member of the growth hormone supergene family in an insoluble or aggregated form; b) lysing the cell by chemical, enzymatic or physical means; c) separating soluble proteins from insoluble or aggregated proteins; d) following step (c) and prior to step (e), dissolving the insoluble or aggregated protein from step (c) in a solution comprising a denaturing agent, a reducing agent and a cysteine blocking agent that forms a reversible mixed disulfide with cysteine, to solubilize and reduce the insoluble or aggregated protein, and to expose the insoluble or aggregated protein to the cysteine blocking agent; and e) refolding the protein by reducing the concentrations of the denaturing agent and reducing agents to levels sufficient to allow the protein to renature into a soluble, biologically active form, wherein said refolding step occurs in the presence of the cysteine blocking agent, and wherein the cysteine blocking agent forms a reversible mixed disulfide with at least one added free cysteine residue in said protein.