JOURNAL OF VIROLOGY

Staropoli I, Dufloo J, Ducher A, Commere PH, Sartori-Rupp A, Novault S, Bruel T, Lorin V, Mouquet H, Schwartz O and Casartelli N.

J Virol. 2019.

doi: 10.1128/JVI.01783-19

This study was peformed using a Simoa® Homebrew assay.

Abstract

The HIV-1 Env protein is exposed at the surface of virions and infected cells. Env fluctuates between different closed and open structural states and these conformations influence both viral infectivity and sensitivity to antibody binding and neutralization. We established a flow virometry assay to visualize Env proteins at the surface of human immunodeficiency virus type 1 (HIV-1) virions. The assay is performed on ultracentrifuged fluorescent viral particles which are stained with a panel of broadly neutralizing (bNAbs) and non-neutralizing antibodies (nnAbs), that probe different epitopes of Env. We used this assay to compare Env at the surface of producer cells and viral particles and to analyze the effect of Nef, CD4 and SERINC5 on Env accessibility to antibodies. We studied the laboratory-adapted strain NL4-3 and two transmitted/founder viruses, THRO and CH058. We confirm that antibody accessibility varies between viral strains and show that Nef, CD4 and SERINC5 additively impact Env conformations. We further demonstrate that Env accessibility profile on virions is globally similar to that observed on HIV-1 infected cells, with some noticeable differences. For instance, nnAbs bind to virions more efficiently than to producer cells, likely reflecting changes in Env conformational states on mature viral particles. This test complements other techniques and provides a convenient and simple tool to quantify and probe the structure of Env at the virion surface and to analyze the impact of viral and cellular proteins on these parameters.

Importance 

HIV-1 Env conformation is one of the key parameters determining viral infectivity. The flow virometry-based assay developed in this study allows for the characterization of proteins incorporated in HIV-1 particles. We studied the conformation of HIV-1 Env and the impact that the viral protein Nef and the cellular proteins CD4 and SERINC5 have on Env accessibility to antibodies. Our assay permitted us to highlight some noticeable differences in the conformation of Env between producer cells and viral particles. It contributes to a better understanding of the actual composition of HIV-1 particles.