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دانلود رایکان مقاله انگلیسی ISI با موضوع لانتی بیوتیک ها: ساختار، بیوسنتز و نحوه عمل

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لانتی بیوتیک ها: ساختار، بیوسنتز و نحوه عمل

عنوان انگلیسی مقاله:

Lantibiotics: structure, biosynthesis and mode of action

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3. Mechanism of action of bacteriocins

In general, the action of bacteriocins produced by Gram-positive bacteria is directed primarily against other Gram-positive species. The range of organisms inhibited by each bacteriocin varies greatly; while nisin is active against a broad variety of bacteria including strains of Lactococcus, Streptococcus, Staphylococcus, Listeria and Mycobacterium, as well as the vegetative cells and outgrowing spores of Bacillus and Clostridium species [2,68,162], the Class II bacteriocin, lactococcin A, speci¢- cally kills lactococci [162,163]. Under normal circumstances, bacteriocins produced by Gram-positive bacteria do not have a bactericidal e¡ect on Gram-negative species. However, in some cases, activity against Gram-negatives can be observed on disruption of the outer membrane, as reported for nisin [165]. It has been established that the primary target for many of these small, cationic peptides is the cytoplasmic membrane of sensitive cells [164,166^170], where they act to dissipate the proton motive force (PMF) through the formation of discrete pores in the cytoplasmic membrane, and thus deprive cells of an essential energy source [171]. The PMF, which is composed of a chemical component (the pH gradient; vpH) and an electrical component (the membrane potential; vi), drives ATP synthesis and the accumulation of ions and other metabolites through PMF-driven transport systems in the membrane [172]. Collapse of the PMF, induced by bacteriocin action, leads to cell death through cessation of energy-requiring reactions. Such a mode of action has been demonstrated for the type-A lantibiotics and the Class II bacteriocins. The type-A lantibiotics act in a voltage-dependent manner without the requirement for a speci¢c protein receptor [173^177]; however, recent work has shown that the activity of nisin is dependent on the concentration of lipid II (undecaprenyl-pyrophosphoryl-MurNAc-(pentapeptide)- GlcNAc) in the membrane of sensitive cells [178,179]. The Class II bacteriocins are thought to interact with membrane receptor proteins prior to insertion into the cytoplasmic membrane in a voltage-independent fashion [164,167]. In contrast, the type-B lantibiotics do not form membrane pores; instead, these peptides act by interfering with essential enzyme activities [180].