Concentration-Dependent Realignment of the Antimicrobial Peptide PGLa in Lipid Membranes Observed by Solid-State ^sup 19^F-NMR

• Published in: Biophysical journal 2005-05, Vol.88 (5), p.3392
• Main Authors: Glaser, Ralf W, Sachse, Carsten, Dürr, Ulrich H N, Wadhwani, Parvesh
• Format: Article
• Language: English
• Subjects: Biochemistry; Biophysics; Lipids; Membranes; Peptides
• ISSN: 0006-3495; 1542-0086

The membrane-disruptive antimicrobial peptide PGLa is found to change its orientation in a dimyristoyl-phosphatidylcholine bilayer when its concentration is increased to biologically active levels. The alignment of the α-helix was determined by highly sensitive solid-state NMR measurements of ^sup 19^F dipolar couplings on CF^sub 3^-labeled side chains, and supported by a nonperturbing ^sup 15^N label. At a low peptide/lipid ratio of 1:200 the amphiphilic peptide resides on the membrane surface in the so-called S-state, as expected. However, at high peptide concentration (≥1:50 molar ratio) the helix axis changes its tilt angle from ~90° to ~120°, with the C-terminus pointing toward the bilayer interior. This tilted "T-state" represents a novel feature of antimicrobial peptides, which is distinct from a membrane-inserted I-state. At intermediate concentration, PGLa is in exchange between the S- and T-state in the timescale of the NMR experiment. In both states the peptide molecules undergo fast rotation around the membrane normal in liquid crystalline bilayers; hence, large peptide aggregates do not form. Very likely the obliquely tilted T-state represents an antiparallel dimer of PGLa that is formed in the membrane at increasing concentration. [PUBLICATION ABSTRACT]