HIV-1 Envelope and MPER Antibody Structures in Lipid Assemblies

Structural and functional studies of HIV envelope glycoprotein (Env) as a transmembrane protein have long been complicated by challenges associated with inherent flexibility of the molecule and the membrane-embedded hydrophobic regions. 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 reconstitute a full-length Env clone into a nanodisc, complex it with a membrane-proximal external region (MPER) targeting antibody 10E8, and structurally define 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 adapt the platform toward vaccine design purposes by introducing stabilizing mutations that allow purification of unliganded Env with a peptidisc scaffold. [Display omitted] •Full-length, wild-type Env incorporated into different lipid assemblies•Structural studies of MPER antibody quaternary epitope in bilayer•Structures reveal a tilting component in the MPER antibody binding mechanism•Assembly platform can be adapted to vaccine design purposes Rantalainen et al. explore approaches to assemble HIV envelope glycoprotein into lipid assemblies, creating a more native environment for structural studies of MPER targeting antibodies. Results illustrate the dynamics of the glycoprotein and show that, in these assemblies, MPER targeting antibodies tilt the glycoprotein in relation to the bilayer.