Antimicrobial activity and bacterial-membrane interaction of ovine-derived cathelicidins

Abstract

Three ovine-derived cathelicidins, SMAP29, OaBac5mini, and OaBac7.5mini, were compared with respect to their antibacterial activities and interactions with membranes. SMAP29 was confirmed to be alpha-helical, broad spectrum, and able to disrupt both the outer and the cytoplasmic membranes at relatively low concentrations. In contrast, the two proline- and arginine-rich OaBac peptides had more-modest antibacterial activities, reduced levels of lipopolysaccharide binding, and a lesser ability to depolarize the cytoplasmic membrane, consistent with a cytoplasmic target.

FIG. 1.

CD spectra of 25 mM SMAP29 (A), 25 mM OaBac5mini (B), and 25 mM OaBac7.5mini (C) in 25 mM phosphate buffer (solid line), 50% 2,2,2-trifluoroethanol (dashed line), and 10 mM lyso-PC-lyso-PG (dotted line). deg, degrees.

FIG. 2.

Release of DiSC₃5 dye from the cytoplasmic membranes of E. coli DC2 cells caused by SMAP29 (×), OaBac5mini (○), and OaBac7.5mini (□). The amount of DiSC₃5 released is given as a percentage of the maximum release of DiSC₃5 caused by gramicidin.