Enterocin C, a class IIb bacteriocin produced by E. faecalis C901, a strain isolated from human colostrum

Enterocin C (EntC), a class IIb bacteriocin was purified from culture supernatants of Enterococcus faecalis C901, a strain isolated from human colostrum. Enterocin C consists of two distinct peptides, named EntC1 and EntC2, whose complementary action is required for full antimicrobial activity. The structural genes entC1 and entC2 encoding enterocins EntC1 and EntC2, respectively, and that encoding the putative immunity protein (EntCI) are located in the 9-kb plasmid pEntC, harboured by E. faecalis C901. The N-terminal sequence of both antimicrobial peptides revealed that EntC1 (4284 Da) is identical to Ent1071A, one of the two peptides that form enterocin 1071 (Ent1071), a bacteriocin produced by E. faecalis BFE 1071. In contrast, EntC2 (3867 Da) presents the non-polar alanine residue at position 17 (Ala(17)) instead of the polar threonine residue (Thr(17)) in Ent1071B, the second peptide constituting Ent1071. In spite of peptide similarities, EntC differs from Ent1071 in major aspects, including the complementary activity among its constitutive peptides and its wider inhibitory spectrum of activity. Different amphiphilic alpha-helical conformations between EntC2 and Ent1071B could explain both, acquired complementary activity and increased antimicrobial spectrum.