Novel serine penicillocarboxypeptidase CPD-S3 from Penicillium janthinellum IBT 3991: Purification, characterization, and uses in peptide synthesis and modification

A novel carboxypeptidase (CPD-S3) from Penicillium janthinellum IBT 3991 has been isolated in a two-step purification procedure by cation exchange and affinity chromatography. The enzyme is a serine carboxypeptidase with a denatured molecular mass determined by SDS of 62 kDa of which 32% is carbohydrate. The isoelectric point is 5.1. CPD-S3 exhibits a high stability towards organic solvents and elevated temperatures. Besides the carboxypeptidase activity, CPD-S3 exhibits esterase, amidase, and carboxamidohydrolase activities. CPD-S3 favors substrates of -configuration with basic amino acid residues in either P₁ or P_1', and particularly dibasic substrates and medium-sized straight-chain alkyl esters for hydrolysis. In aminolysis of esters, amino acid amides and hydrazines coupled in good yield, but methyl esters poorly, and unlike other carboxypeptidases, free amino acids could not be coupled or transpeptidation effected to form amides. In ester semisynthesis, peptides with neutral, but not basic, residues in P₁ could be esterified. The scope of applicability for enzymatic peptide synthesis is limited.