Interactions of the HIV-1 fusion peptide with large unilamellar vesicles and monolayers. A cryo-TEM and spectroscopic study

Abstract

We have examined the interaction of the human immunodeficiency virustype 1 fusion peptide (23 amino acid residues) and of a Trp-containing analog with vesicles composed of dioleoylphosphatidylcholine, dioleoylphosphatidylethanolamine and cholesterol (molar ratio, 1:1:1). Both the native and the Trp-substituted peptides bound the vesicles to the same extent and induced intervesicular lipid mixing with comparable efficiency. Infrared reflection-absorption spectroscopy data are compatible with the adoption by the peptide of a main beta-sheet structure in a cospread lipid/peptide monolayer. Cryo-transmission electron microscopy observations of peptide-treated vesicles reveal the existence of a peculiar morphology consisting of membrane tubular elongations protruding from single vesicles. Tryptophan fluorescence quenching by brominated phospholipids and by water-soluble acrylamide further indicated that the peptide penetrated into the acyl chain region closer to the interface rather than into the bilayer core. We conclude that the differential partition and shallow penetration of the fusion peptide into the outer monolayer of a surface-constrained bilayer may account for the detected morphological effects. Such single monolayer-restricted interaction and its structural consequences are compatible with specific predictions of current theories on viral fusion.

Membrane-Transferring Regions of gp41 as Targets for HIV-1 Fusion Inhibition and Viral Neutralization

“…These studies not only confirm the predicted high affinity of MTRs for the membrane interface, but also support their role as promoters of lipid bilayer destabilization [12,13,34,[36][37][38]. In principle MTR-s might promote fusion by reducing the formation energies of the lipidic intermediates of fusion, and/or by accelerating the opening of fusion pores [39][40][41].…”

“…MTR partitioning into membranes has been quantitatively assessed in vesicular model systems using representative synthetic peptides [12,[29][30][31][32][33][34][35][36][37]. These studies not only confirm the predicted high affinity of MTRs for the membrane interface, but also support their role as promoters of lipid bilayer destabilization [12,13,34,[36][37][38].…”

Solid-State Nuclear Magnetic Resonance Measurements of HIV Fusion Peptide to Lipid Distances Reveal the Intimate Contact of β Strand Peptide with Membranes and the Proximity of the Ala-14−Gly-16 Region with Lipid Headgroups

“…~8.5 Å from the bilayer center and ~10 Å from the lipid phosphorus. Infrared (IR) and solid-state NMR spectra of membrane-associated HFP suggested that the HFP-F8W had predominant β strand conformation under the conditions of the fluorescence experiments (16,27,36,37). In a different set of experiments, electron spin resonance spectra showed that chromium oxalate in the aqueous phase quenched the signal of membrane-associated HFP which was spin-labeled at M19 but did not quench HFP spin-labeled at A1 (30).…”

“…HFP location in membranes has been primarily probed using a HFP-F8W mutant and by variation of the tryptophan fluorescence of this mutant with changes in environment (36,37). Key results have included: (1) fluorescence was higher for membrane-associated HFP-F8W than for HFP-F8W in buffered saline solution; (2) greater fluorescence quenching by acrylamide was observed for a soluble tryptophan analog than for membrane-associated HFP-F8W; and (3) similar fluorescence quenching of membrane-associated HFP-F8W was observed in samples containing either 1-palmitoyl-2-stearoyl-phosphocholine brominated at the 6, 7 carbons of the stearoyl chain or the corresponding lipid brominated at the 11, 12 carbons of the chain.…”

“…~8.5 Å from the bilayer center and ~10 Å from the lipid phosphorus. Infrared (IR) and solid-state NMR spectra of membrane-associated HFP suggested that the HFP-F8W had predominant β strand conformation under the conditions of the fluorescence experiments (16,27,36,37).…”