title: Ligand binding characteristics of CXCR4 incorporated into paramagnetic proteoliposomes.
abstract: The G protein-coupled receptor CXCR4 is a coreceptor, along with CD4, for the human immunodeficiency virus type 1 (HIV-1) and has been implicated in breast cancer metastasis. We studied the binding of the HIV-1 gp120 envelope glycoprotein (gp) to CXCR4 but found that the gp120s from CXCR4-using HIV-1 strains bound nonspecifically to several cell lines lacking human CXCR4 expression. Therefore, we constructed paramagnetic proteoliposomes (CXCR4-PMPLs) containing pure, native CXCR4. CXCR4-PMPLs specifically bound the natural ligand, SDF-1alpha, and the gp120s from CXCR4-using HIV-1 strains. Conformation-dependent anti-CXCR4 antibodies and the CXCR4 antagonist AMD3100 blocked HIV-1 gp120 binding to CXCR4-PMPLs. The gp120-CXCR4 interaction was blocked by anti-gp120 antibodies directed against the third variable (V3) loop and CD4-induced epitopes, structures that have also been implicated in the binding of gp120 to the other HIV-1 coreceptor, CCR5. Compared with the binding of R5 HIV-1 gp120s to CCR5, the gp120-CXCR4 interaction exhibited a lower affinity (K(d) = 200 nm) and was dependent upon prior CD4 binding, even at low temperature. Thus, although similar regions of X4 and R5 HIV-1 gp120s appear to be involved in binding CXCR4 and CCR5, respectively, differences exist in nonspecific binding to cell surfaces, affinity for the chemokine receptor, and CD4 dependence at low temperature.
authors.affiliation: Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, the Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Babcock
authors.forename: T
authors.initials: T
authors.lastname: Mirzabekov
authors.forename: W
authors.initials: W
authors.lastname: Wojtowicz
authors.forename: J
authors.initials: J
authors.lastname: Sodroski
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D015704:CD4 Antigens / Q000378:metabolism; D002460:Cell Line; D002469:Cell Separation; D002478:Cells, Cultured; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D015699:HIV Envelope Protein gp120 / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008024:Ligands; D050356:Lipid Metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D011487:Protein Conformation; D011510:Proteolipids / Q000378:metabolism*; D019713:Receptors, CCR5 / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013950:Thymus Gland / Q000166:cytology; D014162:Transfection
chemical_list: D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D008024:Ligands; D011510:Proteolipids; D019713:Receptors, CCR5; D019718:Receptors, CXCR4; C020485:proteoliposomes