The complete Consensus V3 loop peptide of the envelope protein gp120 of HIV‐1 shows pronounced helical character in solution

Abstract

The disulfide bridge closed cyclic peptide corresponding to the whole Consensus V3 loop of the envelope protein gp120 of HIV-1 was examined by proton 2D-NMR spectroscopy in water and in a 20% trifluoroethanol/water solution. In water, NOE data support a beta-turn conformation for the central conservative GPGR region and point towards partial formation of a helix in the C-terminal part. Upon addition of trifluoroethanol, a C-terminal helix is formed. This is evidenced by NOE data, alpha-proton chemical shift changes and changes in the JN alpha vicinal coupling constants. The C-terminal helix is amphipathic and also occurs in other examined strains. It could therefore be an important feature for the functioning of the V3 loop.