FUNCTIONAL-ROLE OF THE ZIPPER MOTIF REGION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 TRANSMEMBRANE PROTEIN GP41

To study the functional role of the zipper motif region, located in th e N-terminal region of the envelope transmembrane protein of human imm unodeficiency virus type 1, a series of vaccinia virus-expressed mutan t proteins containing a proline substitution in this region were chara cterized. All of the mutant proteins showed partial or no inhibition i n gp160 cleavage, demonstrated impaired ability of gp120 to associate with gp41, and were unable to mediate syncytium formation with CD4(+) cells. Moreover, mutants 580 and 587 secreted excessive gp120 into the medium compared with the wild type. Mutations in this region affected the conformation of the local or proximal sequence but did not alter the conformation conferred by a distal site. These studies reveal the crucial role of the C-terminal segment of the zipper motif region in e nvelope heterodimeric association and suggest that this sequence forms a gp120 contact site.