期刊
BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES
卷 1758, 期 9, 页码 1330-1342出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbamem.2006.02.029
关键词
a-helical peptide; magainin family antimicrobial peptide; solid-state H-2-NMR; alanine-d(3) isotope label; oriented membrane sample; dimerization equilibrium; lipid hydration; DMPC and DMPG
The cationic antimicrobial peptide PGLa is electrostatically attracted to bacterial membranes, binds as an amphiphilic alpha-helix, and is thus able to permeabilize the lipid bilayer. Using solid state H-2-NMR of non-perturbing Ala-d(3) labels on the peptide, we have characterized the helix alignment under a range of different conditions. Even at a very high peptide-to-lipid ratio (1:20) and in the presence of negatively charged lipids, there was no indication of a toroidal wormhole structure. Instead, PGLa re-aligns from a surface-bound S-state to an obliquely tilted T-state, which is presumably dimeric. An intermediate structure half-way between the S- and T-state was observed in fully hydrated multilamellar DMPC vesicles at 1:50, suggesting a fast exchange between the two states on the time scale of > 50 kHz. We demonstrate that this equilibrium is shifted from the S- towards the T-state either upon (i) increasing the peptide concentration, (ii) adding negatively charged DMPG, or (iii) decreasing the level of hydration. The threshold concentration for re-alignment in DMPC is found to be between 1:200 and 1: 100 in oriented samples at 96% humidity. In fully hydrated multilamellar DMPC vesicles, it shifts to an effective peptide-to-lipid ratio of 1:50 as some peptides are able to escape into the bulk water phase. (c) 2006 Elsevier B.V. All rights reserved.
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