title: Characterization of the tertiary structure of soluble CD4 bound to glycosylated full-length HIVgp120 by chemical modification of arginine residues and mass spectrometric analysis.
abstract: The initial step of infection of blood cells with the human immunodeficiency virus, HIV, is the formation of a complex of the viral envelope protein gp120 and its human receptor CD4. We have examined structural features of recombinant soluble CD4 (sCD4) by chemical modification of arginine residues with hydroxyphenylglyoxal and subsequent analysis by matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometry. As R58, R59, R131, R134, R219, R240, R293, and R329 could be derivatized free in solution, these arginine residues were exposed on the surface of the protein. In the noncovalent complex of sCD4 with HIV(SF2)gp120, only R58, R131, R134, R219, R240, R293, and R329 were accessible for the derivatizing agent. R59 was shielded from hydroxyphenylglyoxal and was, therefore, considered to be part of the interaction site with gp120. This indicates that the carbohydrate moieties and the flexible variable loops of the glycosylated full-length gp120 from HIV strain SF2 do not induce a reorganization of CD4 in its binding to gp120 and, therefore, do not appear to significantly affect the structural orientation of the primary receptor in complex with the HIV envelope protein as compared to the binding observed in the crystal structure of CD4 with truncated deglycosylated gp120.
authors.affiliation: Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Hager-Braun
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Tomer
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D015704:CD4 Antigens / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006031:Glycosylation; D015699:HIV Envelope Protein gp120 / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012995:Solubility; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D011994:Recombinant Proteins; D001120:Arginine