This is a family of bacteriocidal bacteriocins secreted by Streptococcal species in order to kill off closely-related competitor Gram-positives. The sequence includes the peptide precursor, this being cleaved off proteolytically at the double-glycine. The family does not carry the YGNGVXC motif characteristic of pediocin-like Bacteriocins, Bacteriocin_II Pfam:PF01721. The producer bacteria are protected from the effects of their own bacteriocins by production of a specific immunity protein which is co-transcribed with the genes encoding the bacteriocins, eg family EntA_Immun Pfam:PF08951. The bacteriocins are structurally more specific than their immunity-protein counterparts. Typically, production of the bacteriocin gene is from within an operon carrying up to 6 genes including a typical two-component regulatory system (R and H), a small peptide pheromone (C), and a dedicated ABC transporter (A and -B) as well as an immunity protein [1]. The ABC transporter is thought to recognise the N termini of both the pheromone and the bacteriocins and to transport these peptides across the cytoplasmic membrane, concurrent with cleavage at the conserved double-glycine motif. Cleaved extracellular C can then bind to the sensor kinase, H, resulting in activation of R and up-regulation of the entire gene cluster via binding to consensus sequences within each promoter [2]. It seems likely that this whole regulon is carried on a transmissible plasmid which is passed between closely related Firmicute species since many clinical isolates from different Firmicutes can produce at least two bacteriocins. and the same bacteriocins can be produced by different species.

1: The blp bacteriocins of Streptococcus pneumoniae mediate intraspecies competition both in vitro and in vivo. Dawid S, Roche AM, Weiser JN; Infect Immun. 2007;75:443-451. PMID:17074857

2: Diversity of enterococcal bacteriocins and their grouping in a new classification scheme. Franz CM, van Belkum MJ, Holzapfel WH, Abriouel H, Galvez A; FEMS Microbiol Rev. 2007;31:293-310. PMID:17298586