Small-Anion Selective Transmembrane "Holes" Induced by an Antimicrobial Peptide Too Short to Span Membranes.

Kan Hu, Yunjiang Jiang, Yuntao Xie, Hui Liu, Rui Liu, Zhi Zhao, Ren Lai, Lihua Yang

Index: J. Phys. Chem. B 119 , 8553-60, (2015)

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Abstract

Whereas many membrane-destabilization modes have been suggested for membrane-spanning antimicrobial peptides (AMPs), few are available for those too short to span membrane thickness. Here we show that ORB-1, a 15-residue disulfide-bridged AMP that is only ∼20 Å long even when fully stretched like a hairpin, may act by inducing small anion-selective transmembrane "holes" of negative mean curvature. In model membranes of Gram-negative bacteria, ORB-1 induces chloride transmembrane transport and formation of transmembrane channels of negative mean curvature, whereas the inactive analogue, ORB-N, does not, suggesting a correlation between antibacterial activity and ability to induce transmembrane channels. Given that ORB-N is the C-terminus amidated form of ORB-1, our results further suggest that formation of membrane-spanning dimers may be required to initiate the observed channel induction. Moreover, ORB-1 renders model bacterial membranes permeable to anions with effective hydration diameters of <1 nm (e.g., Cl(-) and NO3(-)), but not cations of similar sizes (e.g., H3O(+)), indicative of anion-selective transmembrane channels with an effective inner diameter of ≤1 nm. In addition, negative-intrinsic-curvature (NIC) lipids such as phosphoethanolamine (PE) may facilitate the membrane-destabilization process of ORB-1. Our findings may expand current understandings on how AMPs destabilize membranes and facilitate the pharmaceutical development of ORB-1.