Patent ID: 7892787

Claim:
A method of producing somatotropin comprising: (a) expressing a hybrid polypeptide in bacterial cells wherein the hybrid polypeptide comprises ubiquitin and somatotropin; (b) extracting the hybrid polypeptide from the bacterial cells; (c) digesting the extracted hybrid polypeptide with a ubiquitin-cleaving enzyme so as to produce biologically active somatotropin, wherein the ubiquitin-cleaving enzyme is a UBP1 protease mutant containing an amino-acid sequence containing at least one of the modifications selected from the group consisting of: a substitution at position 754 of the UBP1 amino acid sequence, a deletion of at least a portion of the amino acids at positions 1 to 98 of the UBP1 sequence, replacement of the proline at position 415 of the UBP1 sequence with leucine, and replacement of the phenylalanine at position 739 of the UBP1 sequence with leucine, and (d) purifying the produced somatotropin from a protein mixture.