Irregular structure of the HIV fusion peptide in membranes demonstrated by solid-state NMR and MD simulations (original) (raw)

To better understand peptide-induced membrane fusion at a molecular level, we set out to determine the structure of the fusogenic peptide FP23 from the HIV-1 protein gp41 when bound to a lipid bilayer. An established solid-state 19 F nuclear magnetic resonance (NMR) approach was used to collect local orientational constraints from a series of CF 3-phenylglycine-labeled peptide analogues in macroscopically aligned membranes. Fusion assays showed that these 19 F-labels did not significantly affect peptide function. The NMR spectra were characteristic of wellbehaved samples, without any signs of heterogeneity or peptide aggregation at 1:300 in 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). We can conclude from these NMR data that FP23 has a well-defined (time-averaged) conformation and undergoes lateral diffusion in the bilayer plane, presumably as a monomer or small oligomer. Attempts to evaluate its conformation in terms of various secondary structures, however, showed that FP23 does not form any type of regular helix or b-strand. Therefore, allatom molecular dynamics (MD) simulations were carried out using the orientational NMR constraints as pseudo-forces to drive the peptide into a stable alignment and structure. The resulting picture suggests that FP23 can adopt multiple b-turns and insert obliquely into the membrane. Such irregular conformation explains why the structure of the fusion peptide could not be reliably determined by any biophysical method so far. Keywords HIV-1 protein gp41 Á Membrane fusion Á Fusogenic peptides Á Solid-state 19 F-and 2 H-NMR Á b-Stranded secondary structure Á All-atom MD simulations Membrane-active peptides: 455th WE-Heraeus-Seminar and AMP 2010 Workshop.