Lipid interactions and angle of approach to the HIV-1 viral membrane of broadly neutralizing antibody 10E8: Insights for vaccine and therapeutic design

Abstract

Among broadly neutralizing antibodies to HIV, 10E8 exhibits greater neutralizing breadth than most. Consequently, this antibody is the focus of prophylactic/therapeutic development. The 10E8 epitope has been identified as the conserved membrane proximal external region (MPER) of gp41 subunit of the envelope (Env) viral glycoprotein and is a major vaccine target. However, the MPER is proximal to the viral membrane and may be laterally inserted into the membrane in the Env prefusion form. Nevertheless, 10E8 has not been reported to have significant lipid-binding reactivity. Here we report x-ray structures of lipid complexes with 10E8 and a scaffolded MPER construct and mutagenesis studies that provide evidence that the 10E8 epitope is composed of both MPER and lipid. 10E8 engages lipids through a specific lipid head group interaction site and a basic and polar surface on the light chain. In the model that we constructed, the MPER would then be essentially perpendicular to the virion membrane during 10E8 neutralization of HIV-1. As the viral membrane likely also plays a role in selecting for the germline antibody as well as size and residue composition of MPER antibody complementarity determining regions, the identification of lipid interaction sites and the MPER orientation with regard to the viral membrane surface during 10E8 engagement can be of great utility for immunogen and therapeutic design.

HIV-1 Envelope and MPER antibody structures in lipid assemblies

“…Initial contacts of antibody between the Env ectodomain and the lipid surface lead to tilting of Env. This interaction in turn increases the exposure of the MPER peptide by partially lifting it off from the membrane surface ( Figure 4D, S4 and S5), lending support that the membrane-embedded and exposed or lifted conformation of the MPER peptide are both relevant for binding (Fu et al, 2018;Irimia et al, 2017;Kwon et al, 2018a). Binding of additional MPER antibodies eventually raises the whole Env up off the membrane and may contribute to shedding of gp120 as shown in earlier studies (Ruprecht et al, 2011).…”

“…These impressive bNAbs together with the high conservation of MPER sequence has stimulated renewed interest in MPER-targeting vaccine design and the use of MPER antibodies for postexposure prophylaxis. Crystal structures of many MPER Fabs have been solved, alone and in complex with MPER peptide and/or with additional short-tailed lipid headgroups (Irimia et al, 2016;Irimia et al, 2017;Krebs et al, 2019;Williams et al, 2017), [Zhang, L. et. al. An MPER Antibody Neutralizes HIV-1 Using Germline Features Shared Among Donors.…”

Surface-Matrix Screening Identifies Semi-specific Interactions that Improve Potency of a Near Pan-reactive HIV-1-Neutralizing Antibody

“…Diverse studies ranging from electron paramagnetic resonance (EPR) analysis (Song et al, 2009; Sun et al, 2008) to mutational and partitioning analyses (Ofek et al, 2010; Rujas et al, 2017), to crystallographic analysis of Fab in complex with phospholipid headgroups (Irimia et al, 2016, 2017) indicate antibodies 10E8 and 4E10 to co-recognize membrane and MPER peptide. In particular, the orientation suggested by the structure of 10E8 with 1,2 dihexanoyl- sn -glycerol-3-phospho-(1’- rac -glycerol) and scaffolded MPER (Irimia et al, 2017) would position the indole ring of Trp100c HC to extend into the viral lipid membrane (Figure 4A). Examination of the structure of 4E10 with 1,2 dihexanoyl- sn -glycerol-3-phosphate and MPER peptide (Irimia et al, 2016) suggested that a Trp substitution in 4E10 at position 100a HC would be similarly positioned to interact with the viral lipid membrane (Figure 4B).…”

“…(A) Structural model of antibody 10E8v4 recognizing lipid headgroups, as defined by Irimia et al (2017), with hotspot position 100c shown in green.…”

Similarities and differences between native HIV-1 envelope glycoprotein trimers and stabilized soluble trimer mimetics

“…A previous report showed a comparison of soluble and full-length and DCT Env structures [23,30], but differences in antigenicity were not assessed due to limited protein yields. Here, we identified a high expressing full-length Env clone as present in the full-length clone described here, may be desirable because MPER directed antibodies can be very broad and potent [49][50][51]. While we have now produced full-length Env in sufficient quantities for animal immunizations it may be prudent to further engineer the trimer to have a more biased antigenic profile similar to corresponding SOSIP immunogens, for example by building the SOSIP design into full-length Env trimers.…”