The bactericidal activity of pediocin PA-1 is specifically inhibited by a 15-mer fragment that spans the bacteriocin from the center toward the C terminus

Abstract

A 15-mer peptide fragment derived from pediocin PA-1 (from residue 20 to residue 34) specifically inhibited the bactericidal activity of pediocin PA-1. The fragment did not inhibit the pediocin-like bacteriocins sakacin P, leucocin A, and curvacin A to nearly the same extent as it inhibited pediocin PA-1. Enterocin A, however, was also significantly inhibited by this fragment, although not as greatly as pediocin PA-1. This is consistent with the fact that enterocin A contains the longest continuous sequence identical to that of pediocin PA-1 in the region spanned by the fragment. The fragment inhibited pediocin PA-1 to a much greater extent than did the other 29 possible 15-mer fragments that span pediocin PA-1. The results suggest that the fragment-by interacting with the target cells and/or pediocin PA-1-interferes specifically with pediocin-target cell interaction.

FIG. 1

Amino acid sequences of pediocin PA-1 (19), enterocin A (3), curvacin A (2, 28), sakacin P (29), and leucocin A (11). The regions where the sequences are identical to the sequence in pediocin PA-1 are boxed. Regions where the sequences are identical to the sequence of fragment 20 are in black.

FIG. 2

Inhibition of the bactericidal activities of pediocin-like bacteriocins due to the presence of 5 μM peptide fragments derived from pediocin PA-1. Inhibition of the bactericidal activities is quantitated as the increase in MIC due to the presence of a fragment. The increase in MIC is defined as the MIC obtained in the presence of a fragment divided by the MIC obtained in the absence of a fragment. The MICs were between 0.5 and 0.05 nM for all of the bacteriocins in the absence of a fragment, with sakacin P having the highest MIC, enterocin A the lowest, and curvacin A, pediocin PA-1, and leucocin A having MICs between those of sakacin P and enterocin A.

FIG. 3

Inhibition (measured as increase in MIC [see the legend to Fig. 2]) of the bactericidal activities of pediocin-like bacteriocins as a function of increasing amounts of fragment 20. The y axis in the inset has a logarithmic scale, whereas the y axis in the main figure is linear.