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Peptidase family C39 mostly contains bacteriocin-processing endopeptidases from bacteria. The cysteine peptidases in family C39 cleave the "double-glycine" leader peptides from the precursors of various bacteriocins (mostly non-lantibiotic). The cleavage is mediated by the transporter as part of the secretion process. Bacteriocins are antibiotic proteins secreted by some species of bacteria that inhibit the growth of other bacterial species. The bacteriocin is synthesized as a precursor with an N-terminal leader peptide, and processing involves removal of the leader peptide by cleavage at a Gly-Gly bond, followed by translocation of the mature bacteriocin across the cytoplasmic membrane. Most endopeptidases of family C39 are N-terminal domains in larger proteins (ABC transporters) that serve both functions. The proposed protease active site is not conserved in all sub-families.
Jiyao W et al.(2023). "The conserved domain database in 2023.",