Evolution of the HIV-1 envelope glycoproteins with a disulfide bond between gp120 and gp41

BACKGROUND: We previously described the construction of an HIV-1 envelope glycoprotein complex (Env) that is stabilized by an engineered intermolecular disulfide bond (SOS) between gp120 and gp41. The modified Env protein antigenically mimics the functional wild-type Env complex. Here, we explore the effects of the covalent gp120 – gp41 interaction on virus replication and evolution. RESULTS: An HIV-1 molecular clone containing the SOS Env gene was only minimally replication competent, suggesting that the engineered disulfide bond substantially impaired Env function. However, virus evolution occurred in cell culture infections, and it eventually always led to elimination of the intermolecular disulfide bond. In the course of these evolution studies, we identified additional and unusual second-site reversions within gp41. CONCLUSIONS: These evolution paths highlight residues that play an important role in the interaction between gp120 and gp41. Furthermore, our results suggest that a covalent gp120 – gp41 interaction is incompatible with HIV-1 Env function, probably because this impedes conformational changes that are necessary for fusion to occur, which may involve the complete dissociation of gp120 from gp41.