Structure of an HIV-1–neutralizing antibody target, the lipid-bound gp41 envelope membrane proximal region trimer

Abstract

The membrane proximal external region (MPER) of HIV-1 glycoprotein (gp) 41 is involved in viral-host cell membrane fusion. It contains short amino acid sequences that are binding sites for the HIV-1 broadly neutralizing antibodies 2F5, 4E10, and 10E8, making these binding sites important targets for HIV-1 vaccine development. We report a high-resolution structure of a designed MPER trimer assembled on a detergent micelle. The NMR solution structure of this trimeric domain, designated gp41-M-MAT, shows that the three MPER peptides each adopt symmetric α-helical conformations exposing the amino acid side chains of the antibody binding sites. The helices are closely associated at their N termini, bend between the 2F5 and 4E10 epitopes, and gradually separate toward the C termini, where they associate with the membrane. The mAbs 2F5 and 4E10 bind gp41-M-MAT with nanomolar affinities, consistent with the substantial exposure of their respective epitopes in the trimer structure. The traditional structure determination of gp41-M-MAT using the Xplor-NIH protocol was validated by independently determining the structure using the DISCO sparse-data protocol, which exploits geometric arrangement algorithms that guarantee to compute all structures and assignments that satisfy the data.

The Atomic Structure of the HIV-1 gp41 Transmembrane Domain and Its Connection to the Immunogenic Membrane-proximal External Region

“…At the N terminus, the hinge segment 671 NWFD 674 (33) is partially extended, consistent with the conformational flexibility put forward by previous NMR studies (24,26,29,33,34). This element is followed by a continuous ␣-helix extending to Gly-690.…”

A Fusion Intermediate gp41 Immunogen Elicits Neutralizing Antibodies to HIV-1

“…The potential fitting might indicate either that HR2 adopted the intermediate conformation in the crystal structure due to the absence of MPER or that this region does not change substantially in the absence of gp120. Alternatively, because of the low resolution of the SAXS model, the fit may be by chance, and the Cys-loop region and HR2 may adopt a completely different conformation and/or may accommodate MPER in an extended conformation (105). The bottom end of the SAXS structure is not accounted for by the gp41 coordinates, and we hypothesize that it contains MPER connected to the transmembrane region.…”

Virus-induced preferential antibody gene-usage and its importance in humoral autoimmunity

“…The proposed mechanism of selection of this particular germline is that the hydrophobic pattern of VH1-69 antibodies allows the binding to the so-called conserved membrane proximal external region (MPER) of HIV gp41 [31][32][33]. The MPER is in close contact to the viral envelope, highly conserved and essential for viral fusion with host cells [34]. In addition, this region is particularly rich in hydrophobic residues possibly driving the preferential selection of neutralizing VH1-69 antibodies directed against MPER [35][36][37].…”