This class of bacteriocins was previously described as class V. The members include gassericin A, acidocin B and butyrovibriocin AR10, all of which are hydrophobic cyclical structures [1]. The N- and C-termini are covalently linked, and the circular molecule is resistant to several proteases and peptidases [2]. The immunity protein that protects Lactobacillus gasseri from the toxic effects of its bacteriocin, gassericin A, has been identified. It is found to be a small positively-charged hydrophobic peptide of 53 amino acids containing a putative transmembrane segment [3] - a structure unlike that of the more common immunity proteins as found in Pfam:PF08951.

1: Genetic analysis of acidocin B, a novel bacteriocin produced by Lactobacillus acidophilus. Leer RJ, van der Vossen JM, van Giezen M, van Noort JM, Pouwels PH; Microbiology. 1995;141:1629-1635. PMID:7551031

2: 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

3: DNA sequencing and homologous expression of a small peptide conferring immunity to gassericin A, a circular bacteriocin produced by Lactobacillus gasseri LA39. Kawai Y, Kusnadi J, Kemperman R, Kok J, Ito Y, Endo M, Arakawa K, Uchida H, Nishimura J, Kitazawa H, Saito T; Appl Environ Microbiol. 2009;75:1324-1330. PMID:19114506