Class II bacteriocin

One important and well studied class of bacteriocins is the class IIa or pediocin-like bacteriocins produced by lactic acid bacteria. All class IIa bacteriocins are produced by food-associated strains, isolated from a variety of food products of industrial and natural origins, including meat products, dairy products and vegetables. Class IIa bacteriocins are all cationic, display anti-Listeria activity, and kill target cells by permeabilizing the cell membrane.[2][3][4]

Class IIa bacteriocins contain between 37 and 48 residues.[5] Based on their primary structures, the peptide chains of class IIa bacteriocins may be divided roughly into two regions: a hydrophilic, cationic and highly conserved N-terminal region, and a less conserved hydrophobic/amphiphilic C-terminal region. The N-terminal region contains the conserved Y-G-N-G-V/L 'pediocin box' motif and two conserved cysteine residues joined by a disulfide bridge. It forms a three-stranded antiparallel beta-sheet supported by the conserved disulfide bridge. This cationic N-terminal beta-sheet domain mediates binding of the class IIa bacteriocin to the target cell membrane. The C-terminal region forms a hairpin-like domain that penetrates into the hydrophobic part of the target cell membrane, thereby mediating leakage through the membrane. The two domains are joined by a hinge, which enables movement of the domains relative to each other.[3][4]

Some proteins known to belong to the class IIa bacteriocin family are listed below:

• Pediococcus acidilactici pediocin PA-1.[6]
• Leuconostoc mesenteroides mesentericin Y105.
• Carnobacterium piscicola carnobacteriocin B2.
• Lactobacillus sakei sakacin P.
• Enterococcus faecium enterocin A.
• Enterococcus faecium enterocin P.
• Leuconostoc gelidum leucocin A.
• Lactobacillus curvatus curvacin A.[7]
• Listeria innocua listeriocin 743A.

The class IIb bacteriocins (two-peptide bacteriocins) require two different peptides for activity. It includes the alpha enterocins and lactococcin G peptides. These peptides have some antimicrobial properties; they inhibit the growth of Enterococcus spp. and a few other Gram-positive bacteria. These peptides act as pore-forming toxins that create cell membrane channels through a barrel-stave mechanism and thus produce an ionic imbalance in the cell[8]

Bacteriocin_IIc
x-ray structure of bacteriocin as-48 at ph 4.5. sulphate bound form
Identifiers
Symbol	Bacteriocin_IIc
Pfam	PF09221
InterPro	IPR009086
SCOP2	1o82 / SCOPe / SUPFAM
TCDB	1.C.28
OPM superfamily	77
OPM protein	1o82
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Other class II bacteriocins can be grouped together as Class IIc (circular bacteriocins). These have a wide range of effects on membrane permeability, cell wall formation and pheromone actions of target cells. In particular, Bacteriocin AS-48 is a cyclic peptide antibiotic produced by the eubacteria Enterococcus faecalis (Streptococcus faecalis) that shows a broad antimicrobial spectrum against both Gram-positive and Gram-negative bacteria. Bacteriocin AS-48 is encoded by the pheromone-responsive plasmid pMB2, and acts on the plasma membrane in which it opens pores leading to ion leakage and cell death.[9] The globular structure of bacteriocin AS-48 consists of five alpha helices enclosing a hydrophobic core. The mammalian NK-lysin effector protein of T and natural killer cells has a similar structure, though it lacks sequence homology with bacteriocins AS-48.

1. Papathanasopoulos, M. A.; Dykes, G. A.; Revol-Junelles, A. M.; Delfour, A.; Von Holy, A.; Hastings, J. W. (1998). "Sequence and structural relationships of leucocins A-, B- and C-TA33a from Leuconostoc mesenteroides TA33a". Microbiology. 144 (5): 1343–1348. doi:10.1099/00221287-144-5-1343. PMID 9611809.
2. Fregeau Gallagher, N. L.; Sailer, M.; Niemczura, W. P.; Nakashima, T. T.; Stiles, M. E.; Vederas, J. C. (1997). "Three-Dimensional Structure of Leucocin a in Trifluoroethanol and Dodecylphosphocholine Micelles: Spatial Location of Residues Critical for Biological Activity in Type IIa Bacteriocins from Lactic Acid Bacteria†,‡". Biochemistry. 36 (49): 15062–15072. doi:10.1021/bi971263h. PMID 9398233.

Class II bacteriocin and related families is variously recorded in Pfam and InterPro as:

The naming is inconsistent at times.