Quaternary protein mimetics of gp41 elicit neutralizing antibodies against HIV fusion-active intermediate state.

During viral entry, the fusogenic state of human immunodeficiency virus Type 1 (HIV-1) envelope protein gp41 is a quaternary structure consisting of three gp41 glycoproteins, each with two conserved helical domains (N-HR and C-HR). Thus far, the examination of monomeric gp41 peptides as an immunologically focused approach to vaccine design has not been successful. Here we report an approach using quaternary protein mimetics (called 3 alpha mimetics) that are based on the gp41 N-HR and C-HR domains to closely mimic the fusogenic state and overcome the deficiencies of the monomeric peptide approach for synthetic vaccine design. The 3 alpha mimetics are conveniently prepared by chemoselective ligation of unprotected monomeric peptides to an interstrand linker, and display enhanced conformational stability compared to the corresponding monomers. The 3 alpha mimetics with or without a covalently attached T-helper epitope were immunogenic and elicited antisera that bound both recombinant gp160, which contains gp41, and HIV-1 virions and immunoprecipitated recombinant gp41. Anti-3 alpha mimetic antisera neutralized viral infectivity against R5- and X4- tropic strains of HIV-1 at 31.5 degrees C. The results suggest that a quaternary protein approach to mimic conserved and functional domains of viral envelope proteins is desirable for HIV vaccine development as such antigens are more likely to produce immunologically-focused and broadly neutralizing antibody responses. (c) 2008 Wiley Periodicals, Inc.