title: Carbohydrate specificity and salt-bridge mediated conformational change in acidic winged bean agglutinin.
abstract: Structures of two crystal forms of the dimeric acidic winged bean agglutinin (WBAII) complexed with methyl-alpha-D-galactose have been determined at 3.0 A and 3.3 A resolution. The subunit structure and dimerisation of the lectin are similar to those of the basic lectin from winged bean (WBAI) and the lectin from Erythrina corallodendron (EcorL). The conformation of a loop and its orientation with respect to the rest of the molecule in WBAII are, however, different from those in all the other legume lectins of known structure. This difference appears to have been caused by the formation of two strategically placed salt bridges in the former. Modelling based on the crystal structures provides a rationale for the specificity of the lectin, which is very different from that of WBAI, for the H-antigenic determinant responsible for O blood group reactivity. It also leads to a qualitative explanation for the thermodynamic data on sugar-binding to the lectin, with special emphasis on the role of a tyrosyl residue in the variable loop in the sugar-binding region in generating the carbohydrate specificity of WBAII.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India.
authors.forename: N
authors.initials: N
authors.lastname: Manoj
authors.forename: V R
authors.initials: VR
authors.lastname: Srinivas
authors.forename: A
authors.initials: A
authors.lastname: Surolia
authors.forename: M
authors.initials: M
authors.lastname: Vijayan
authors.forename: K
authors.initials: K
authors.lastname: Suguna
mesh_terms: D000017:ABO Blood-Group System / Q000276:immunology; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019281:Dimerization; D007887:Fabaceae / Q000737:chemistry*; D006031:Glycosylation; D037102:Lectins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008024:Ligands; D019684:Magnoliopsida / Q000737:chemistry; D008756:Methylgalactosides / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D008958:Models, Molecular; D009844:Oligosaccharides / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D037121:Plant Lectins; D010946:Plants, Medicinal; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits; D012492:Salts / Q000737:chemistry / Q000378:metabolism*; D055672:Static Electricity; D013379:Substrate Specificity; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism
chemical_list: D000017:ABO Blood-Group System; D037102:Lectins; D008024:Ligands; D008756:Methylgalactosides; D009844:Oligosaccharides; D037121:Plant Lectins; D021122:Protein Subunits; D012492:Salts; C049304:winged bean lectin; D014443:Tyrosine