Disruption of the HIV-1 Envelope allosteric network blocks CD4-induced rearrangements

Rory Henderson,Kevin O Saunders,Kevin Wiehe,Allen L Hsu,Zekun Mu,Scott C Blanchard,S Munir Alam,Mario J Borgnia,Maolin Lu,R J Edwards,Barton F Haynes,Alberto Bartesaghi,Qifeng Han,Ye Zhou,Priyamvada Acharya,Elizabeth Carter,Walther Mothes,Robert Parks

doi:10.1038/s41467-019-14196-w

Abstract

The trimeric HIV-1 Envelope protein (Env) mediates viral-host cell fusion via a network of conformational transitions, with allosteric elements in each protomer orchestrating host receptor-induced exposure of the co-receptor binding site and fusion elements. To understand the molecular details of this allostery, here, we introduce Env mutations aimed to prevent CD4-induced rearrangements in the HIV-1 BG505 Env trimer. Binding analysis and single−molecule Förster Resonance Energy Transfer confirm that these mutations prevent CD4-induced transitions of the HIV-1 Env. Structural analysis by single−particle cryo-electron microscopy performed on the BG505 SOSIP mutant Env proteins shows rearrangements in the gp120 topological layer contacts with gp41. Displacement of a conserved tryptophan (W571) from its typical pocket in these Env mutants renders the Env insensitive to CD4 binding. These results reveal the critical function of W571 as a conformational switch in Env allostery and receptor-mediated viral entry and provide insights on Env conformation that are relevant for vaccine design.

Highlights

The trimeric HIV-1 Envelope protein (Env) mediates viral-host cell fusion via a network of conformational transitions, with allosteric elements in each protomer orchestrating host receptor-induced exposure of the co-receptor binding site and fusion elements
We reasoned that design of stabilized Env trimers based on an understanding of BMS-626529-mediated stabilization could lead to mutations that inhibit CD4 triggering for both the soluble SOSIP and membrane-bound Envs
The F-series mutations were designed to block CD4-triggering, we reasoned that V3 exposure may occur even in the absence of full triggering of the Env[34] and examined residues in the V1/V2 to V3 contact region for mutagenesis to lock V3 in its prefusion, V1/V2-coupled state

Summary

Introduction

The trimeric HIV-1 Envelope protein (Env) mediates viral-host cell fusion via a network of conformational transitions, with allosteric elements in each protomer orchestrating host receptor-induced exposure of the co-receptor binding site and fusion elements. Additional structural information from antibody-stabilized, potential closed-toopen state intermediates in SOSIP trimers suggests trimer opening occurs through ordered conformational transitions[31] Despite these advances in our understanding of Env transitions, atomic level details of the allosteric mechanism by which CD4 induces transitions in the Env has remained elusive, limiting our ability to leverage such a mechanism for the development of vaccine immunogens. Structure determination via single particle cryo-EM revealed key details regarding how allosteric elements downstream from the gp120-CD4 contact control transitions of the trimer between the Env closed and open states These results provide a means by which to control the Env conformational ensemble and reveal details required for understanding the conformational plasticity of the HIV-1 Env

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Conclusion