THE COMPLETE CONSENSUS V3 LOOP PEPTIDE OF THE ENVELOPE PROTEIN GP120 OF HIV-1 SHOWS PRONOUNCED HELICAL CHARACTER IN SOLUTION

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/w ater solution. In water, NOE data support a beta-turn conformation for the central conservative GPGR region and point towards partial format ion of a helix in the C-terminal part. Upon addition of trifluoroethan ol, a C-terminal helix is formed. This is evidenced by NOE data, alpha -proton chemical shift changes and changes in the J(N alpha) vicinal c oupling 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.