Streptococcus parasanguis pepO encodes an endopeptidase with structure andactivity similar to those of enzymes that modulate peptide receptor signaling in eukaryotic cells

Studies in our laboratory have identified two fimbria-associated adhesins, FimA and Fap1, of Streptococcus parasanguis FW213. In this study, me isolat ed and sequenced DNA fragments linked to fimA to determine if they containe d additional factors associated with adherence, virulence, or survival in t he host. An open reading frame just upstream and divergently transcribed fr om the fim4 operon was identified and named pepO. Northern hybridization in dicated that pepO is transcribed as a monocistronic message. pepO encodes a predicted 631-amino-acid protein with a molecular mass of approximately 70 .6 kDa. PepO contains the essential motif HEXXH, typical of many zinc-depen dent metalloproteases and metallopeptidases. PepO has significant sequence identity to mammalian metallopeptidases, including endothelin-converting en zyme, which converts a potent vasoconstrictor into its active form, and neu tral endopeptidase (NEP), which is involved in terminating the activity of opioid peptides. The opioid peptide metenkephalin is a natural substrate of NEP. Cell extracts of FW213 cleaved metenkephalin at the same site as does NEP, while an extract from an insertionally inactivated pepO mutant did no t. These results indicate that FW213 pepO encodes an enzyme with activity s imilar to that of known mammalian endopeptidases. Phylogenetic analysis of PepO and its homologues suggests lateral genetic exchange between bacteria and eukaryotes.