Class II Non-Lantibiotic Bacteriocins

Fig. 4. Representative class II non-lantibiotic bacteriocin operons. The class II non-lantibio-tic bacteriocins include lactococcin A, B> M and G [46,125,126,128,135,136], lactacin F [77], pediocin PA-1 and AcH [62, 130, 131], mesentericin Y105 [124], sakacin A [133] and plantaricin A [49, 134], The structural genes are highlighted as black arrowheads. Genes with similar proposed function or substantial sequence similarity are highlighted in the same manner. The arrowheads indicate the direction of transcription. The function of MesC, and SapOSTUV of the mesentericin Y150 and plantaricin A operons is unknown...

Fig. 5. The amino acid sequence of the putative induction fectors of class II non-lantibiotic bacteriocins plantaricin A, sakacin A and P and carnobacteriocin A [28]...

Fig. 9. Maturation pathway of a class II non-lantibiotic bacteriocin presented as a 4-step process. The HPK and RR constitute a protein complex involved in signal transduction of external stimuli (step 1), resulting in transcription and translation of the bacteriocin precursor (step 2). The inactive precursor peptide is targeted to a membrane anchored ATP dependent translocation complex and processing at the double-glycine consensus site occurs intracellularly (step 3) and is followed by secretion (step 4). The role of the accessory protein in this mechanism is not yet understood... 

While class II non-lantibiotic bacteriocins appear to be secreted by the sec-independent universal ABC transporter system, it has recently been shown that some bacteriocins do not possess a double-glycine leader peptide but are, instead, synthesized with a typical W-terminal leader peptide of the sec-type. So far four such sec-dependent bacteriocins have been reported divergicin A [51], acidocin B (50], bacteriocin 31 [208] and enterocin P [209]. Recently, two bacteriocins, enterocin L50A and L50B, were found to be secreted without an N-terminal leader sequence or signal peptide [210]. 

Rgure 5.1. Classification scheme of the bacteriocins of Gram (+) bacteria, revised from Cotter et al. (2005b). The main distinction is made between the Class I lantibiotics, which undergo extensive post-translational modifications, and the Class II non-modified bacteriocins. The amino acid sequence and structural features of one example bacteriocin of each different class are shown. 

Peptide bacteriocins produced by lactic acid bacteria are categorized into two different classes according to their biochemical and genetic properties (Drider et al. 2006 Nes et al. 2007). Class I peptides are the lantibiotics, which are small, post-translationally modified peptides that contain unusual amino acids such as lanthionine (TC 1.C.20). Class II includes unmodified bacteriocins that are subdivided into three subclasses, namely, class Ha (pediocin-like bacteriocins), class Ilb (two-peptide bacteriocins), and He (other (i.e., non-pediocin-like), one-peptide bacteriocins). 

Most antimicrobial peptides produced by Gram-positive bacteria are classified as bacteriocins, and like microcins they are diverse in size and structure.35 36 Recent classification schemes divide bacteriocins into three classes lantibiotics (class I), heat-stable non-lantibiotics (class II) and heat-labile antimicrobial proteins (class III), of which the majority of bacteriocins belong either to class I or class II. NMR spectroscopy has been applied in numerous studies of bacteriocins and an overview of the range of diversity in the 3D structures that have been determined by NMR spectroscopy is provided in Figure 4. 

Class II bacteriocins heat stable non-lantibiotic peptides... 

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