A specific inhibitor of cysteine proteases impairs a Vif-dependent modification of human immunodeficiency virus type 1 Env protein.

The Vif protein of human immunodeficiency virus type 1 (HIV-1) regulates viral infectivity. Virions produced in cell culture after transfection by a Vif-negative molecular clone show a dramatic decrease in infectivity for susceptible CD4+ cell lines, although the Vif protein does not appear to be a constituent of the viral particle. The exact mechanism by which Vif affects HIV-1 infectivity is so far unknown. We report the existence of structural homologies between Vif and a family of cysteine proteases and present evidence which suggests that one of the targets of Vif is the Env protein and more precisely the cytoplasmic domain of gp41. Vif was found to modify both the processing and conformation of the Env protein. Ethyl(25, 35)- 3[(5)-3-methyl-1-(3-methylbutylcarbamoyl)]oxirane-2-carboxylate, a specific inhibitor of cysteine proteases, inhibits the effect of Vif, as does the mutation of Cys-114 to Leu in Vif. Furthermore, Cys-114 of Vif produced in Escherichia coli, interacts directly with trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane. These observations suggest that a cysteine protease activity is associated with Vif and that this activity plays a role in Env maturation.