HIV-1 Envelope and MPER antibody structures in lipid assemblies

Abstract

<jats:title>Summary</jats:title><jats:p>Structural and functional studies of HIV Env as a transmembrane protein have long been complicated by challenges associated with inherent flexibility of the molecule and the membrane-embedded hydrophobic regions. Thus, most structural studies have utilized soluble forms where the regions C-terminal to the ectodomain are deleted. Here, we present approaches for incorporating full-length, wild-type HIV-1 Env, as well as C-terminally truncated and stabilized versions, into lipid assemblies, providing a modular platform for Env structural studies by single particle electron microscopy. We reconstituted a full-length Env clone into a nanodisc with MSP1D1 scaffold, complexed it with an MPER targeting antibody 10E8, and structurally defined the full quaternary epitope of 10E8 consisting of lipid, MPER and ectodomain contacts. By aligning this and other Env-MPER antibody complex reconstructions with the lipid bilayer, we observe evidence of Env tilting as part of the neutralization mechanism for MPER-targeting antibodies. We also adapted the platform toward vaccine design purposes by introducing stabilizing mutations that allow purification of unliganded Env with peptidisc scaffold.</jats:p>

Neutralizing Antibodies Targeting HIV-1 gp41

“…Ample structural data suggest that the current structures of the Env ectodomain based on the SOSIP design [ 5 , 6 ] represent the native Env prefusion conformation [ 7 , 8 , 9 ]. The conformation observed in Env SOSIP structures is in agreement with medium resolution structures of membrane-bound Env [ 10 ] and membrane-anchored Env solubilized in detergent or nanodiscs [ 11 , 12 , 13 ]. In addition, an alternative conformation that precedes the SOSIP conformation has been proposed to explain some discrepancies on antibody binding to membrane-anchored versus soluble Env [ 14 , 15 ].…”

“…MPER is likely sterically occluded within native Env and only accessible upon initial receptor-induced conformational changes [ 79 , 80 ]. Nevertheless, a first encounter complex can be formed with native Env, which however induces conformational changes to facilitate access to the epitope [ 11 , 12 ]. MPER bnAb-Env structures [ 11 , 12 ] suggest further that trimeric MPER [ 64 ] needs to “open” up to accommodate bnAb binding.…”

“…Nevertheless, a first encounter complex can be formed with native Env, which however induces conformational changes to facilitate access to the epitope [ 11 , 12 ]. MPER bnAb-Env structures [ 11 , 12 ] suggest further that trimeric MPER [ 64 ] needs to “open” up to accommodate bnAb binding. In addition, the different approach angles of MPER bnAbs indicates that MPER is likely in a “monomeric” conformation upon bnAb binding [ 40 ].…”

Structure of HIV-1 gp41 with its membrane anchors targeted by neutralizing antibodies

“…Our data, thus, indicate that MPER antibodies can act all along the gp41 refolding pathway from blocking initial conformations of close to native Env [68][69][70] up to a late fusion intermediate state that has already pulled viral and cellular membranes into close apposition. This thus, opens a long temporal window of action for MPER bnAbs consistent with the findings that the half-life of neutralization of MPER bnAbs is up to 30 minutes post virus exposure to target cells 71,72 .…”

Structure, membrane topology and influence of cholesterol of the membrane proximal region: transmembrane helical anchor sequence of gp41 from HIV

“…Mutagenesis of CRAC resulted in a reduced infection rate and a slowing of the viral life cycle 34 . Notably, epitopes for the 2F5, 4E10, 10E8 and LN01 broadly neutralizing antibodies against HIV include locations of the MPER and knowing more about its structure bears considerable promise for the rational design of an AIDS vaccine [35][36][37][38][39][40] .…”