Broadly Neutralizing Anti-HIV Antibody 4E10 Recognizes a Helical Conformation of a Highly Conserved Fusion-Associated Motif in gp41

Abstract

Broadly neutralizing monoclonal antibodies to HIV-1 are rare but invaluable for vaccine design. 4E10 is the broadest neutralizing antibody known and recognizes a contiguous and highly conserved epitope in the membrane-proximal region of gp41. The crystal structure of Fab 4E10 was determined at 2.2 A resolution in complex with a 13-residue peptide containing the gp41 core epitope (NWFDIT). The bound peptide adopts a helical conformation in which the key contact residues, TrpP672, PheP673, IleP675, and ThrP676, map to one face of the helix. The peptide binds in a hydrophobic pocket that may emulate its potential interaction with the host cell membrane. The long CDR H3 of the antibody extends beyond the bound peptide in an orientation that suggests that its apex could contact the viral membrane when 4E10 is bound to its membrane-proximal epitope. These structural insights should assist in the design of immunogens to elicit 4E10-like neutralizing responses.

Immunogenicity of recombinant human immunodeficiency virus type 1-like particles expressing gp41 derivatives in a pre-fusion state

“…The extended helical structure of an MPER peptide, KWASLWNWFNITNWLWYIK in DPC micelles was also revealed by an NMR study offering a model of possible interaction of this region with the membrane [45]. More recently, a crystal structure of a 4E10 Fab in complex with a peptide bearing the sequence, WNWFDITNW revealed its major contact residue segment, WFDIT to be in a helical conformation [46]. A further study showed improved 4E10 binding affinity to a helix-stabilized peptide relative to the starting untethered peptide [47].…”

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

“…These core epitopes were determined by peptide mapping; however, alanine-scanning mutagenesis of the MPER in intact viruses established that only a few residues (D664/K665/W666, W672/F673/W680, and N671/ D674 HXB2 numbering throughout) are essential for 2F5, 4E10, and Z13e1 neutralization, respectively (7,9). Crystal structures of Fab 2F5, 4E10, and Z13e1 complexed with their respective epitope peptides subsequently confirmed that residues DKW, WFW, and ND are buried in the paratopes of these antibodies (10)(11)(12)(13)(14).…”

“…We opted to first mutate residues at the apex of the CDRH3 because previously described crystal structures of Fab 4E10 complexed to an epitope peptide revealed that this region does not form part of the antigen binding site as is often the case for a CDRH3 (14,30). A similar study was not implemented for 2F5, because the case for 2F5-lipid interactions is less clear, its very occurrence a topic of current debate (21,27,31).…”

A fusion-intermediate state of HIV-1 gp41 targeted by broadly neutralizing antibodies

“…Moreover, much of the antibody response may be to rearranged or dissociated forms of gp120 and gp41, on which the dominant epitopes may be either in hypervariable loops or in positions occluded on virion-borne envelope trimer. Rare, ''broadly neutralizing'' antibodies have been detected that recognize one of three relatively conserved regions on the envelope protein: the CD4-binding site (mAb b12) (2); carbohydrates on the outer gp120 surface (mAb 2G12) (3); and a segment of the gp41 ectodomain adjacent to the viral membrane (mAbs 2F5 and 4E10) (4,5), often called the ''membrane-proximal external region'' (MPER). We seek to understand the molecular mechanisms of neutralization by these and other antibodies.…”