Importance of the Membrane-Perturbing Properties of the Membrane-Proximal External Region of Human Immunodeficiency Virus Type 1 gp41 to Viral Fusion

Abstract

The membrane-proximal external region (MPER; K 665 WASLWNWFNITNWLWYIK 683 ) of the human immunodeficiency virus type 1 (HIV-1) gp41 ectodomain plays a critical role in envelope glycoproteinmediated fusion. In addition, the epitopes of important neutralizing antibodies (2F5, Z13, and 4E10) and the sequence of the peptide fusion inhibitor T20 overlap this conserved region. The MPER has an unusually high percentage of tryptophan residues that likely contribute to the membrane-disrupting nature of the region, which is predicted to adopt an ␣-helical conformation on membrane contact. We have investigated the membrane-disruptive requirements for this region using a panel of mutants that replace most of the MPER with antibacterial, membrane-active peptides. The results demonstrate that the mutant Envs were processed, transported, and expressed on the cell surface similar to wild type. Some of the mutant Envs induced moderate levels of cell-cell fusion, demonstrating that the region can accommodate the substitution of proline-rich foreign peptides while retaining significant biological function. In contrast, the incorporation into and stability of the mutated Envs in virions was reduced, consistent with the severely impaired viral entry observed for all the mutants. These data suggest that both structural (for Env incorporation) and functional (membrane disruption) constraints may contribute to the highly conserved nature of this region.

Binding of Anti-Membrane-Proximal gp41 Monoclonal Antibodies to CD4-Liganded and -Unliganded Human Immunodeficiency Virus Type 1 and Simian Immunodeficiency Virus Virions

“…Despite extensive analyses of the MPER peptides (5,36,47,49,79), the in vivo/in situ structure of this region of the Env spike is unknown for any stage of the prefusion/fusion sequence. The hydrophobic nature of the MPER suggests a significant association with the lipid bilayer (30,42,57,77).…”

Cholesterol-Dependent Membrane Fusion Induced by the gp41 Membrane-Proximal External Region–Transmembrane Domain Connection Suggests a Mechanism for Broad HIV-1 Neutralization

“…Thus, it has been argued that, beyond the anchoring effect, the N-terminal FP inserted into the target membrane could generate the focal points of dehydration and hydrophobic destabilization required for fusion (recently reviewed in reference 14). Complementarily, it has been suggested that shallow insertion of MPER into the envelope external leaflet might prime the opposing viral membrane for fusion (16)(17)(18)(19). Supporting its conservation and functionality, the MPER comprises one of the four "sites of vulnerability" targeted by broadly neutralizing antibodies within the Env glycoprotein and the only one existing within the gp41 subunit (reviewed in references 20 and 21).…”

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

“…Some of the produced gp41 chimeras indeed retained fusion activity [90], therefore demonstrating that MPER can be replaced by a membrane-disruptive foreign sequence and preserve its biological function.…”

“…The functional importance of MPER lytic activity for gp41-induced fusion has been recently demonstrated by Vishwanathan and Hunter [90]. These authors designed gp41 chimeras that replaced all or part of MPER with indolicidin-based sequences.…”