Mechanism of HIV-1 Env neutralization by antibodies targeting the membrane-proximal external region

Yale University, New Haven CT

Investigators

Abstract

SUMMARY Human immunodeficiency virus type 1 (HIV-1) remains a major global public health concern, despite advances in treatment, there is no vaccine and no cure. The challenge in developing a vaccine is primarily due to HIV-1’s high mutation rates, resulting in a diverse viral strains, an effective glycan shield and conformational masking of functional centers on its glycoprotein. The HIV-1 envelope glycoprotein (Env) mediates viral entry into host cells at the beginning of the infection cycle. Although Env exhibits great sequence variation and shield by glycans, some patients developed broadly neutralizing antibodies (bnAbs) that target conserved elements of Env. Among bnAbs, antibodies targeting the membrane-proximal external region (MPER) are highly effective, exhibit good breadth, and immunogens eliciting these antibodies have resulted in encouraging in vivo data. Previous structural studies using purified Env embedded in nanodiscs have provided insights into how bnAbs bind to the MPER. However, much less is known about the interaction of anti-MPER bnAbs with native virus particles. In this study, we will use cryo-electron tomography (cryo-ET) combined with molecular dynamics (MD) simulations to elucidate how anti-MPER bnAbs engage Env in native virus particles, and determine how they interfere with virus-host membrane fusion. Our preliminary study revealed that three DH511 Fab molecules could simultaneously bind to a tilted Env with all three Fabs approaching Env from one side. Thus, MPER regions exhibit great conformational flexibility and can reach the opposite side of the trimer. Upon addition of CD4 and 17b, DH511 binding to Env increased, and an additional mode is observed whereby three DH511 Fab molecules symmetrically bind to an upright Env. In this study, we will characterize the structural basis of how anti-MPER bnAbs bind the unliganded HIV-1 Env on native virions. Additionally, we will define the dynamics of how anti-MPER bnAbs access Env epitopes upon binding of CD4. We will investigate both Fab and IgG forms of the antibodies, in the presence of either soluble CD4 (sCD4) or membrane-bound CD4. MD simulations will provide atomic models corresponding to the cryo-ET density maps. Finally, we will elucidate the mechanism by which MPER antibodies interfere with membrane fusion.