Identification and characterization of an extracellular protease activity produced by the marine Vibrio sp. 60

The marine fish pathogen Vibrio sp. 60 has been used as a host for heterologous expression of the Escherichia coli heat-labile enterotoxin B-subunit and derivatives carrying a C-terminal extension. In this study, a chimeric enterotoxin B-subunit with an extension corresponding to the carboxy-terminal nine amino acids -Tyr-Ala-Gly-Ala-Val-Val-Asn-Asp-Leu-COOH from the small subunit of herpes simplex virus type 1-encoded ribonucleotide reductase, is shown to be proteolytically cleaved in the extracellular medium by a single virus type 1-encoded ribonucleotide reductase, is shown to be proteolytically cleaved in the extracellular medium by a single protease that is secreted by the host strain. Such protease behaves as a typical metalloprotease, being inhibited by EDTA but not by a serine protease inhibitor. Purification and amino acid composition analysis of the two proteolysis products revealed a specific cleavage of the peptide bond between amino acids glycine and alanine of the nine amino acid extension with loss of activity. The above observation is relevant for the biotechnological exploitation of Vibrio sp. 60.