Cyclic V3‐loop‐related HIV‐1 conjugate vaccines Synthesis, conformation and immunological properties

Abstract

Branched undecapeptides with sequences related to the virus glycoprotein V3 domain sequences of the MN and IIIB variants of HIV-1 were synthesized and cyclized with a peptide (amide) closure to cyclic decapeptides. Two-dimensional NMR studies allowed protons for the MN variant-related cycle (L-697,250) to be assigned. Molecular modelling with distance geometry methods permitted a conformation to be identified which showed good agreement with ROESY and 2D NMR study data. A molecular dynamics simulation showed that the highly conserved loop tip sequence (Gly-Pro-Gly-Arg) was in a conventional beta-turn less than 50% of the time. For evaluation of immunogenicity and antibody characterization studies, covalent carrier conjugates were prepared. 3-Maleimidopropionylation of the Nle amino group of the cyclic peptides gave an electrophilic tether which captured a thiol group from a thiolated carrier protein, OMPC (outer membrane protein complex of Neisseria meningitidis). Through the use of a novel co-conjugation procedure, soluble immunogen-carrier molecules were prepared which had suitable physical properties for use as a vaccine. These V3-loop-based vaccines could elicit neutralizing antibody, but not consistently in all animals. Characterization of sera showed that responses were broadly virus neutralizing.