A C-Terminal Disulfide Bridge in Pediocin-Like Bacteriocins Renders Bacteriocin Activity Less Temperature Dependent and Is a Major Determinant of the Antimicrobial Spectrum

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Abstract
Several lactic acid bacteria produce so-called pediocin-like bacteriocins that share sequence characteristics, but differ in activity and target cell specificity. The significance of a C-terminal disulfide bridge present in only a few of these bacteriocins was studied by site-directed mutagenesis of pediocin PA-1 (which naturally contains the bridge) and sakacin P (which lacks the bridge). Introduction of the C-terminal bridge into sakacin P broadened the target cell specificity of this bacteriocin, as illustrated by the fact that the mutants were 10 to 20 times more potent than the wild-type toward certain indicator strains, whereas the potency toward other indicator strains remained essentially unchanged. Like pediocin PA-1, disulfide-containing sakacin P mutants had the same potency at 20 and 37°C, whereas wild-type sakacin P was approximately 10 times less potent at 37°C than at 20°C. Reciprocal effects on target cell specificity and the temperature dependence of potency were observed upon studying the effect of removing the C-terminal disulfide bridge from pediocin PA-1 by Cys→Ser mutations. These results clearly show that a C-terminal disulfide bridge in pediocin-like bacteriocins contributes to widening of the antimicrobial spectrum as well as to higher potency at elevated temperatures. Interestingly, the differences between sakacin P and pediocin PA-1 in terms of the temperature dependency of their activities correlated well with the optimal temperatures for bacteriocin production and growth of the bacteriocin-producing strain.

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