title: Inhibition of the HIV-1 spike by single-PG9/16-antibody binding suggests a coordinated-activation model for its three protomeric units.
abstract: The HIV-1 spike is composed of three protomeric units, each containing a peripheral gp120 and a transmembrane gp41 subunit. Binding to the CD4 and the chemokine receptors triggers them to mediate virus entry into cells by membrane fusion. The spikes also represent the major target for neutralizing antibodies (Abs) against the virus. We have studied how two related broadly neutralizing Abs, PG9 and PG16, react with the spike. Unexpectedly, this also suggested how the functions of the individual protomers in the spike depend on each other. The Abs have been shown to bind the V1/V2 loops of gp120, located at the top of the spike. Using blue native-polyacrylamide gel electrophoresis (BN-PAGE), we show that only single Abs or antigen-binding fragments could bind to the spikes of HIV-1 virus-like particles. Apparently, binding to one gp120 sterically interferes with binding to the other two subunits in the spike top. Despite this constraint, all of the protomers of the spike became resistant to CD4 binding and subsequent formation of the coreceptor binding site. These activities were measured by monitoring the sequential complex formation of the spike first with Abs and then with soluble 2d- or 4d-CD4 or with soluble CD4 and the CD4 inducible coreceptor binding site Ab 17b in BN-PAGE. The inhibition of the spike by single-Ab binding suggested that the activation reactions of the individual protomeric units are linked to each other in a coordinated activation process.
authors.affiliation: Department of Biosciences and Nutrition, Karolinska Institute, Huddinge, Sweden.
authors.forename: Robin
authors.initials: R
authors.lastname: Löving
authors.forename: Mathilda
authors.initials: M
authors.lastname: Sjöberg
authors.forename: Shang-Rung
authors.initials: SR
authors.lastname: Wu
authors.forename: James M
authors.initials: JM
authors.lastname: Binley
authors.forename: Henrik
authors.initials: H
authors.lastname: Garoff
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology / Q000378:metabolism*; D057134:Antibodies, Neutralizing / Q000276:immunology / Q000378:metabolism*; D001665:Binding Sites; D015704:CD4 Antigens / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D015699:HIV Envelope Protein gp120 / Q000276:immunology / Q000378:metabolism*; D015700:HIV Envelope Protein gp41 / Q000276:immunology / Q000378:metabolism*; D015497:HIV-1 / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology / Q000378:metabolism; D063347:Native Polyacrylamide Gel Electrophoresis / Q000379:methods; D011485:Protein Binding; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D053586:Virus Internalization; D054299:env Gene Products, Human Immunodeficiency Virus / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing; D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D015700:HIV Envelope Protein gp41; D007140:Immunoglobulin Fab Fragments; D011994:Recombinant Proteins; D054299:env Gene Products, Human Immunodeficiency Virus; C076613:recombinant soluble CD4