title: Characterization of a discontinuous epitope of the HIV envelope protein gp120 recognized by a human monoclonal antibody using chemical modification and mass spectrometric analysis.
abstract: A subset of the neutralizing anti-HIV antibodies recognize epitopes on the envelope protein gp120 of the human immunodeficiency virus. These epitopes are exposed during conformational changes when gp120 binds to its primary receptor CD4. Based on chemical modification of lysine and arginine residues followed by mass spectrometric analysis, we determined the epitope on gp120 recognized by the human monoclonal antibody 559/64-D, which was previously found to be specific for the CD4 binding domain. Twenty-four lysine and arginine residues in recombinant full-length glycosylated gp120 were characterized; the relative reactivities of two lysine residues and five arginine residues were affected by the binding of 559/64-D. The data show that the epitope is discontinuous and is located in the proximity of the CD4-binding site. Additionally, the reactivities of a residue that is located in the secondary receptor binding region and several residues distant from the CD4 binding site were also altered by Ab binding. These data suggest that binding of 559/64-D induced conformational changes which result in altered surface exposure of specific amino acids distant from the CD4-binding site. Consequently, binding of 559/64-D to gp120 affects not only the CD4-binding site, which is recognized as the epitope, but appears to have a global effect on surface exposed residues of the full-length glycosylated gp120.
authors.affiliation: Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Sciences, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Hager-Braun
authors.forename: Elisabeth O
authors.initials: EO
authors.lastname: Hochleitner
authors.forename: Miroslaw K
authors.initials: MK
authors.lastname: Gorny
authors.forename: Susan
authors.initials: S
authors.lastname: Zolla-Pazner
authors.forename: Rachelle J
authors.initials: RJ
authors.lastname: Bienstock
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Tomer
mesh_terms: D000107:Acetylation; D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000378:metabolism*; D001120:Arginine / Q000737:chemistry / Q000378:metabolism; D015704:CD4 Antigens / Q000737:chemistry / Q000378:metabolism; D018604:Epitope Mapping / Q000379:methods*; D000939:Epitopes / Q000737:chemistry* / Q000378:metabolism; D006031:Glycosylation; D015699:HIV Envelope Protein gp120 / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008239:Lysine / Q000737:chemistry / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation
chemical_list: D000911:Antibodies, Monoclonal; D015704:CD4 Antigens; D000939:Epitopes; D015699:HIV Envelope Protein gp120; C514793:gp120 protein, Human immunodeficiency virus 1; D001120:Arginine; D008239:Lysine