Members of this family are membrane-interacting peptides, produced by Firmicutes that display a broad anti-microbial spectrum against Gram-positive and Gram-negative bacteria. They adopt a helical structure, with four or five alpha helices forming a Saposin-like fold [2,5]. The structure has been found to be cyclical [1, 3, 5]. It should be pointed out that one reference [4] implies that both circularin A and gassericin A are class V or IIc-type bacteriocins; however we find that these two proteins fall into different Pfam families families, this one and BacteriocIIc_cy, Pfam:PF12173.

1: Identification and characterization of two novel clostridial bacteriocins, circularin A and closticin 574. Kemperman R, Kuipers A, Karsens H, Nauta A, Kuipers O, Kok J; Appl Environ Microbiol. 2003;69:1589-1597. PMID:12620847

2: Structure of bacteriocin AS-48: from soluble state to membrane bound state. Sanchez-Barrena MJ, Martinez-Ripoll M, Galvez A, Valdivia E, Maqueda M, Cruz V, Albert A; J Mol Biol. 2003;334:541-549. PMID:14623193

3: Uberolysin: a novel cyclic bacteriocin produced by Streptococcus uberis. Wirawan RE, Swanson KM, Kleffmann T, Jack RW, Tagg JR; Microbiology. 2007;153:1619-1630. PMID:17464077

4: The circular bacteriocins gassericin A and circularin A. Kawai Y, Kemperman R, Kok J, Saito T; Curr Protein Pept Sci. 2004;5:393-398. PMID:15544534

5: The three-dimensional structure of carnocyclin A reveals that many circular bacteriocins share a common structural motif. Martin-Visscher LA, Gong X, Duszyk M, Vederas JC; J Biol Chem. 2009;284:28674-28681. PMID:19692336