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Journal of Virology, October 2008, p. 10032-10041, Vol. 82, No. 20
0022-538X/08/$08.00+0     doi:10.1128/JVI.01050-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Sequestering of the Prehairpin Intermediate of gp41 by Peptide N36^Mut(e,g) Potentiates the Human Immunodeficiency Virus Type 1 Neutralizing Activity of Monoclonal Antibodies Directed against the N-Terminal Helical Repeat of gp41

Laboratories of Chemical Physics,¹ Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520²

Received 19 May 2008/ Accepted 23 July 2008

Human immunodeficiency virus type 1 (HIV-1) neutralization can be effected by several classes of inhibitors that target distinct regions of gp41 that are accessible in the prehairpin intermediate (PHI) state and block the formation of the six-helix bundle (6-HB) conformation of gp41. The N-heptad repeat (N-HR) of gp41 is the site of action of two classes of inhibitors. One class binds to the trimeric N-HR coiled coil, while the other, exemplified by the peptide N36^Mut(e,g), disrupts the trimer and sequesters the PHI through the formation of heterotrimers. We recently reported a neutralizing Fab (Fab 3674), selected from a nonimmune phage library, that binds to the trimeric N-HR coiled coil through an epitope that remains exposed in the 6-HB and is also present in heterotrimers of the N-HR and N36^Mut(e,g) peptide. Here we show that N36^Mut(e,g) prolongs the temporal window during which the virus is susceptible to neutralization by the bivalent Fab 3674 and that bivalent Fab 3674 and N36^Mut(e,g) neutralize HXB2 and SF162 strains of HIV-1, as well as isolates of diverse primary B and C HIV-1 strains, synergistically in a Env-pseudotyped virus neutralization assay. N36^Mut(e,g) also rescues neutralizing activity of Fab 3674 against resistant virus strains and renders a series of related nonneutralizing Fabs neutralizing. Moreover, N36^Mut(e,g) exhibits the same effects on the broadly neutralizing 2F5 and 4E10 monoclonal antibodies directed against the membrane-proximal extended region of gp41. The mechanistic implications of these findings are discussed.

Published ahead of print on 30 July 2008.