title: Irregular structure of the HIV fusion peptide in membranes demonstrated by solid-state NMR and MD simulations.
abstract: 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 well-behaved 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 β-strand. Therefore, all-atom 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 β-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.
authors.affiliation: Karlsruhe Institute of Technology, Institute of Organic Chemistry and CFN, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany.
authors.forename: Dorit
authors.initials: D
authors.lastname: Grasnick
authors.forename: Ulrich
authors.initials: U
authors.lastname: Sternberg
authors.forename: Erik
authors.initials: E
authors.lastname: Strandberg
authors.forename: Parvesh
authors.initials: P
authors.lastname: Wadhwani
authors.forename: Anne S
authors.initials: AS
authors.lastname: Ulrich
mesh_terms: D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry / Q000378:metabolism; D015700:HIV Envelope Protein gp41 / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D015658:HIV Infections / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D015497:HIV-1 / Q000254:growth & development / Q000378:metabolism; D006801:Humans; D007553:Isotope Labeling; D008051:Lipid Bilayers / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D050576:Membrane Fusion Proteins / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D017433:Protein Structure, Secondary
chemical_list: D015700:HIV Envelope Protein gp41; D008051:Lipid Bilayers; D050576:Membrane Fusion Proteins; D004134:Dimyristoylphosphatidylcholine