Conformational mapping of the N‐terminal peptide of HIV‐1 gp41 in lipid detergent and aqueous environments using ¹³C‐enhanced Fourier transform infrared spectroscopy

Abstract

The N-terminal domain of HIV-1 glycoprotein 41,000 (gp41) participates in viral fusion processes. Here, we use physical and computational methodologies to examine the secondary structure of a peptide based on the N terminus (FP; residues 1-23) in aqueous and detergent environments.12 C-Fourier transform infrared (FTIR) spectroscopy indicated greater ␣-helix for FP in lipid-detergent sodium dodecyl sulfate (SDS) and aqueous phosphate-buffered saline (PBS) than in only PBS. 12C-FTIR spectra also showed disordered FP conformations in these two environments, along with substantial ␤-structure for FP alone in PBS. In experiments that map conformations to specific residues, isotope-enhanced FTIR spectroscopy was performed using FP peptides labeled with 13 C-carbonyl.13 C-FTIR results on FP in SDS at low peptide loading indicated ␣-helix (residues 5 to 16) and disordered conformations (residues 1-4). Because earlier 13 C-FTIR analysis of FP in lipid bilayers demonstrated ␣-helix for residues 1-16 at low peptide loading, the FP structure in SDS micelles only approximates that found for FP with membranes. Molecular dynamics simulations of FP in an explicit SDS micelle indicate that the fraying of the first three to four residues may be due to the FP helix moving to one end of the micelle. In PBS alone, however, electron microscopy of FP showed large fibrils, while 13 C-FTIR spectra demonstrated antiparallel ␤-sheet for FP (residues 1-12), analogous to that reported for amyloid peptides. Because FP and amyloid peptides each exhibit plaque formation, ␣-helix to ␤-sheet interconversion, and membrane fusion activity, amyloid and N-terminal gp41 peptides may belong to the same superfamily of proteins.

The HIV-Neutralizing Monoclonal Antibody 4E10 Recognizes N-Terminal Sequences on the Native Antigen

“…The crystal structure of this peptide bound to 4E10 verifies a helical conformation, in which the hydrophobic residues are located on one face of the helix (9). The fusogenic peptide, however, could adopt an ␣-helical shape or a ␤-sheet conformation depending on the peptide concentration and environmental factors such as type of lipids or the presence of cations (21)(22)(23)(24)(25)(26). The PTMR as well as the N-terminal regions of gp120 and gp41 contain several hydrophobic residues.…”

Conformational Flexibility and Strand Arrangements of the Membrane-Associated HIV Fusion Peptide Trimer Probed by Solid-State NMR Spectroscopy

“…Models for the helical structure have been developed based on nuclear magnetic resonance (NMR), electron spin resonance (ESR), infrared (IR), and circular dichroism (CD) data, as well as computer simulations (33)(34)(35)(36)(37)(38)(39). A β hairpin model for non-helical structure has been proposed based on IR and surface activity measurements in membranes (40).…”

“…Other investigators have developed structural models for the helical form of the peptides based principally on liquid-state NMR, ESR, and IR data (33,38,39,73,74). IR and solid-state NMR studies of the β strand form of HFP and its oligomeric constructs have shown parallel strand arrangement, anti-parallel strand arrangement and a mixture of parallel and antiparallel arrangements (26,43,44).…”

How can a β‐sheet peptide be both a potent antimicrobial and harmfully toxic? Molecular dynamics simulations of protegrin‐1 in micelles

“…Also, we have previously studied the HIV-1 fusion peptide FP-1 in an SDS micelle, 22,31 and the antimicrobial ovispirin and its derivatives in both SDS and DPC. 32,33 We detail here the simulation method used, present the results, and discuss the hypotheses we can generate about the activity and toxicity of protegrin-1.…”