A new serine protease family with elastase activity is produced by Streptomyces bacteria

We found an elastolytic activity in the culture supernatant of Streptomyces sp. P-3, and the corresponding enzyme (streptomycetes elastase, SEL) was purified to apparent homogeneity from the culture supernatant. The molecular mass of purified SEL was approximately 18 kDa as judged by SDS-PAGE analysis and gel-filtration chromatography. Utilizing information from N-terminal amino acid sequencing of SEL and mass spectrometry of SEL tryptic fragments, we succeeded in cloning the gene-encoding SEL. The cloned SEL gene contains a 726 bp ORF, which encodes a 241 amino acid polypeptide containing a putative signal peptide for secretion (28 amino acid) and pro-sequence (14 amino acid). Although the deduced primary structure of SEL has sequence similarity to proteins in the S1 protease family, the amino acid sequence shares low identity (< 31.5 %) with any known elastase. SEL efficiently hydrolyses synthetic peptides having Ala or Val in the P1 position such as N-succinyl-Ala-Ala-(Pro or Val)-Ala-p-nitroanilide (pNA), whereas reported proteases by streptomycetes having elastolytic activity prefer large residues, such as Phe and Leu. Compared of kcat/Km ratios for Suc-Ala-Ala-Val-Ala-pNA and Suc-Ala-Ala-Pro-Ala-pNA with subtilisin YaB, which has high elastolytic activity, Streptomyces sp. P-3 SEL exhibits 12- and 121-fold higher, respectively. Phylogenetic analyses indicate that the predicted SEL protein, together with predicted proteins in streptomycetes, constitutes a novel group within the S1 serine protease family. These characteristics suggest that SEL-like proteins are new members of the S1 serine protease family, which display elastolytic activity.