HIV-1 Broadly Neutralizing Antibody Extracts Its Epitope from a Kinked gp41 Ectodomain Region on the Viral Membrane

Abstract

Although rarely elicited during natural human infection, the most broadly neutralizing antibodies (BNAbs) against diverse human immunodeficiency virus (HIV)-1 strains target the membrane-proximal ectodomain region (MPER) of viral gp41. To gain insight into MPER antigenicity, immunogenicity, and viral function, we studied its structure in the lipid environment by a combination of nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and surface plasmon resonance (SPR) techniques. The analyses revealed a tilted N-terminal alpha helix (aa 664-672) connected via a short hinge to a flat C-terminal helical segment (675-683). This metastable L-shaped structure is immersed in viral membrane and, therefore, less accessible to immune attack. Nonetheless, the 4E10 BNAb extracts buried W672 and F673 after initial encounter with the surface-embedded MPER. The data suggest how BNAbs may perturb tryptophan residue-associated viral fusion involving the mobile N-terminal MPER segment and, given conservation of MPER sequences in HIV-1, HIV-2, and SIV, have important implications for structure-guided vaccine design.

Membrane-Transferring Regions of gp41 as Targets for HIV-1 Fusion Inhibition and Viral Neutralization

“…Within this continuous structure, residues W672 and F673 face towards the HC region of the membrane. A comparable orientation of these residues was observed within the bipartite structure reported by Sun et al [93] (PDB entry: 2PV6). This structure might be representative of longer MPER specimens, such as AISpreTM, bearing higher polarity at the N-terminus.…”

“…Lorizate et al [105] reported surface pressure measurements compatible with the partial extraction by 4E10 of PreTM peptide from lipid monolayers (see also Figure 4) and Sun et al [93] provided electron-paramagnetic resonance data compatible with 4E10 epitope extraction from the longer 662-683 MPER peptide inserted into lipid bilayers. These authors observed that extracted W672 and F673 side chains rearrange within the 4E10 paratope, and that, particularly the latter residue, flips vertically and inserts deeply into the epitope-binding pocket.…”

“…Subsequent analyses of the MPER sequence including the application of the hydrophobic-at-interface moment to the numerous mutations generated by Salzwedel and coworkers [17] revealed that this gp41 MTR might be segmented into two A more recent DPC-NMR structure reported by Sun et al [93] provided the structural basis for the functional segmentation of this gp41 MTR (see also Figure 3A, right panel). The MPER sequence 662 ELDKWASLWNWFNITNWLWYIK 683 analyzed by these authors was elongated at the N-terminus by including the E662 and D664 polar residues.…”

“…These authors observed that extracted W672 and F673 side chains rearrange within the 4E10 paratope, and that, particularly the latter residue, flips vertically and inserts deeply into the epitope-binding pocket. Sun et al [93] also hypothesized that solvent exposed N671…”

Aromatic residues at the edge of the antibody combining site facilitate viral glycoprotein recognition through membrane interactions

“…Since then, a number of membraneassociated MPER peptide structures have been resolved using NMR spectroscopy methods (19)(20)(21). Given the caveat that unbound MPER NMR structures are contextually dissociated from the macromolecular structure of native, trimeric, envelope spikes, and until a high-resolution structure of Env on intact viruses is attained, in situ MPER membrane association remains an open question.…”