A Monomeric 3₁₀-Helix Is Formed in Water by a 13-Residue Peptide Representing the Neutralizing Determinant of HIV-1 on gp41^,

Abstract

The peptide gp41(659-671) (ELLELDKWASLWN) comprises the entire epitope for one of the three known antibodies capable of neutralizing a broad spectrum of primary HIV-1 isolates and is the only such epitope that is sequential. Here we present the NMR structure of gp41(659-671) in water. This peptide forms a monomeric 3(10)-helix stabilized by i,i+3 side chain-side chain interactions favored by its primary sequence. In this conformation the peptide presents an exposed surface, which is mostly hydrophobic and consists of conserved HIV-1 residues. The presence of the 3(10)-helix is confirmed by its characteristic CD pattern. Studies of the 3(10)-helix have been hampered by the absence of a model peptide adopting this conformation. gp41(659-671) can serve as such a model to investigate the spectral characteristics of the 3(10)-helix, the factors that influence its stability, and the propensity of different amino acids to form a 3(10)-helix. The observation that the 3(10)-helical conformation is highly populated in the peptide gp41(659-671) indicates that the corresponding segment in the cognate protein is an autonomous folding unit. As such, it is very likely that the helical conformation is maintained in gp41 throughout the different tertiary structures of the envelope protein that form during the process of viral fusion. However, the exposure of the gp41(659-671) segment may vary, leading to changes in the reactivity of anti-gp41 antibodies in the different stages of viral fusion. Since gp41(659-671) is an autonomous folding unit, peptide immunogens consisting of the complete gp41(659-671) sequence are likely to induce antibodies highly cross-reactive with HIV-1.

UV Resonance Raman Investigation of a 310-Helical Peptide Reveals a Rough Energy Landscape

“…On average, in proteins, 3-4% of peptide residues occur in a 3 10 -helix conformation (48). The 3 10 -helix differs from an R-helix in that the tighter packing of the backbone forces the CdO‚‚‚H-N hydrogen bonds to point outward, away from the helical axis, resulting in decreased stability of the 3 10 -helix compared to that of the R-helix (25,48).Recent ESR (39, 42) and NMR (43) work by Millhauser et al (41) suggests the presence of 3 10 -helix at the terminus of short alanine-based helical peptides. The authors proposed that 3 10 -helices are a relic of the folding process.…”

“…On average, in proteins, 3-4% of peptide residues occur in a 3 10 -helix conformation (48). The 3 10 -helix differs from an R-helix in that the tighter packing of the backbone forces the CdO‚‚‚H-N hydrogen bonds to point outward, away from the helical axis, resulting in decreased stability of the 3 10 -helix compared to that of the R-helix (25,48).…”

“…Unfortunately, the conformation dynamics of peptides with unnatural amino acids may be irrelevant for the study of biological problems. In this context, the recent discovery of Biron et al of an all-natural amino acid tridecapeptide, gp41 [659][660][661][662][663][664][665][666][667][668][669][670][671] (48), that folds into a 3 10 -helix is greatly significant since it enables the study of 3 10 -helices. gp41 659-671 is a 13-residue peptide with the sequence E 659 -LLELDKWAS 669 LWN extracted from glycoprotein gp41 of HIV-1, corresponding to residues 659-671.…”

“…gp41 659-671 is a 13-residue peptide with the sequence E 659 -LLELDKWAS 669 LWN extracted from glycoprotein gp41 of HIV-1, corresponding to residues 659-671. NOE constraints indicate that in water at 277 K, the monomeric form of the peptide folds into a nine-residue 3 10 -helix (48). Biron et al proposed that the 3 10 -helix is stabilized by favorable hydrophobic stacking interactions between L663, W666, L669, and W670 (48).…”

“…NOE constraints indicate that in water at 277 K, the monomeric form of the peptide folds into a nine-residue 3 10 -helix (48). Biron et al proposed that the 3 10 -helix is stabilized by favorable hydrophobic stacking interactions between L663, W666, L669, and W670 (48). Residues E662, K665, S668, and N671 form the polar face where E662 and K665 may engage in weak electrostatic interactions.…”