title: Binding of anti-membrane-proximal gp41 monoclonal antibodies to CD4-liganded and -unliganded human immunodeficiency virus type 1 and simian immunodeficiency virus virions.
abstract: The broadly neutralizing monoclonal antibodies (MAbs) 4E10, 2F5, and Z13e1 target membrane-proximal external region (MPER) epitopes of HIV-1 gp41 in a manner that remains controversial. The requirements for initial lipid bilayer binding and/or CD4 ligation have been proposed. To further investigate these issues, we probed for binding of these MAbs to human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) virions with protein A-conjugated gold (PAG) nanoparticles using negative-stain electron microscopy. We found moderate levels of PAG associated with unliganded HIV-1 and SIV virions incubated with the three MAbs. Significantly higher levels of PAG were associated with CD4-liganded HIV-1 (epitope-positive) but not SIV (epitope-negative) virions. A chimeric SIV virion displaying the HIV-1 4E10 epitope also showed significantly higher PAG association after CD4 ligation and incubation with 4E10. MAbs accumulated rapidly on CD4-liganded virions and slowly on unliganded virions, although both reached similar levels in time. Anti-MPER epitope-specific binding was stable to washout. Virions incubated with an irrelevant MAb or CD4-only (no MAb) showed negligible PAG association, as did a vesicle-rich fraction devoid of virions. Preincubation with Fab 4E10 inhibited both specific and nonspecific 4E10 IgG binding. Our data provide evidence for moderate association of anti-MPER MAbs to viral surfaces but not lipid vesicles, even in the absence of cognate epitopes. Significantly greater MAb interaction occurs in epitope-positive virions following long incubation or CD4 ligation. These findings are consistent with a two-stage binding model where these anti-MPER MAbs bind first to the viral lipid bilayer and then to the MPER epitopes following spontaneous or induced exposure.
authors.affiliation: Department of Biological Science and Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, USA.
authors.forename: Ramesh
authors.initials: R
authors.lastname: Rathinakumar
authors.forename: Moumita
authors.initials: M
authors.lastname: Dutta
authors.forename: Ping
authors.initials: P
authors.lastname: Zhu
authors.forename: Welkin E
authors.initials: WE
authors.lastname: Johnson
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Roux
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology*; D001666:Binding Sites, Antibody; D015704:CD4 Antigens / Q000276:immunology*; D015700:HIV Envelope Protein gp41 / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology*; D008024:Ligands; D008854:Microscopy, Electron; D015302:Simian Immunodeficiency Virus / Q000276:immunology*; D014771:Virion / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D015704:CD4 Antigens; D015700:HIV Envelope Protein gp41; D008024:Ligands
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