Class IIB Bacteriocins

Two bacteriodns and an immunity protein, organized in one operon, comparable with the lactococcin M operon, were detected in the case of lactacin F, lactococcin G, and in two operons (plnEFI and plnJKLR) of the plantaricin A gene cluster. All four depend on complementation of two bacteriocin peptides for highest activity and therefore belong to the class IIB bacteriodns [46,49, 124,128]. 

Purification of lactococdn G identified two peptides, a and p, that individually exhibited marginal levels of activity. Upon complementation of the two peptides in a 7a ip ratio, a seven-fold increase in activity was noted [47]. AUison et al. [48] proved that lactacin F activity and host range were expanded upon the complementation of two heterologously expressed peptides of the lactacin F operon, although initially only one bioactive peptide (LafA) was purified 

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The voltage independent activity of lactococcin B, similar to thiol-activated toxins, was proposed to be dependent on the reduced state of its unique cysteine residue on position 24 [71]. Recently, it was shown by means of protein engineering that the Cys-24 residue was not necessary for activity of lactococcin B [28]. Lactococcin G is a novel lactococcal class IIB bacteriocin whose activity depends on the action of two peptides [47]. The combination of the a and P peptide dissipated the membrane potential, induced a dramatic decrease in the cellular ATP level, and resulted in a rapid efflux of potassium [72]. 

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