Oral Presentation 2014 International Biophysics Congress

Structure and membrane topology of the pore-forming peptide maculatin 1.1 depend on lipid composition (#118)

Marc-Antoine Sani 1 , Frances Separovic 1
  1. University of Melbourne, Melbourne, VIC, Australia

Antimicrobial peptides (AMP) that target membranes are an attractive alternative to classic antibiotics, since they do not require internalization nor target a specific stereo-structure, thus limiting development of bacterial resistance. Their mode of action involves the disruption of lipid membranes, however, the molecular details of the killing mechanism and, more particularly, the difference in potency observed between different bacterial strains, remain unclear. We present the structural investigation of the AMP maculatin 1.1 (Mac1) in different lipid systems. Using solution and solid-state NMR with paramagnetic relaxation enhancement (PRE) agents and dye release (DR) experiments, we demonstrate the important role of the lipid composition in modulating the structure and location of Mac1. HSQC of specifically 15N labeled Mac1 in buffer displayed a narrow chemical shift dispersion that is typical of random coil structures. Introduction of DPC, DPC/LPG and DHPC micelles, DHPC/DMPC and DHPC/DMPC/DMPG isotropic (q = 0.5) bicelles produced chemical shift dispersions characteristic of helical structures, with differences suggesting that Mac1 adopts a different degree of helicity dependent on the curvature and membrane charge surface. 3D TROSY-NOESY allowed assignment of the sequential 15N labeled residues, and determination of a 3D helical structure in DPC micelles and DHPC/DMPC bicelles, the latter producing the greatest helical stretch. Titration of the PRE agent Gd3+-(DTPA) into the Mac1–DHPC/DMPC system showed that the central core of Mac1 is mainly transmembrane. In DHPC/DMPC/DMPG anisotropic (q = 4) bicelles, Mac1 induced greater headgroup and acyl-chain perturbation for DMPG than DMPC. In terms of activity, Mac1 induced greater leakage in neutral membranes, except for highly ordered lipid compositions, than with negatively charged membranes. However, in a competitive environment, electrostatic interactions determined the activity of Mac1, reducing the interaction with neutral membranes but these interactions are not sufficient to explain fully the specific bactericidal activity of AMP.