FUNCTIONAL-CHARACTERIZATION OF PEDIOCIN PA-1 BINDING TO LIPOSOMES IN THE ABSENCE OF A PROTEIN-RECEPTOR AND ITS RELATIONSHIP TO A PREDICTED TERTIARY STRUCTURE

The physicochemical interaction of pediocin PA-1 with target membranes was characterized using lipid vesicles made from the total lipids ext racted from Listeria monocytogenes. Pediocin PA-1 caused the time- and concentration-dependent release of entrapped carboxyfluorescein (CF) from the vesicles. The pediocin-induced CF efflux rates were higher un der acidic conditions than under neutral and alkaline conditions and w ere dependent on both pediocin and lipid concentrations. A binding iso therm constructed on the basis of the Langmuir isotherm gave an appare nt binding constant of 1.4x10(7) M(-1) at pH 6.0. The imposition of a transmembrane potential (inside negative) increased the CF efflux rate by 88%. Pediocin PA-1 also permeablized synthetic vesicles composed o nly of phosphatidylcholine. Sequence alignments and secondary-structur e predictions for the N terminus of pediocin PA-1 and other class IIa bacteriocins predicted that pediocin PA-1 contained two beta-sheets ma intained in a hairpin conformation stabilized by a disulfide bridge. T he structural model also revealed patches of positively charged residu es, consistent with the argument that electrostatic interactions play an important role in the binding of pediocin PA-1 to the lipid vesicle s. This study demonstrates that pediocin PA-1 can function in the abse nce of a protein receptor and provides a structural model consistent w ith these results.