title: Role of second metal ion in establishing active conformations of concanavalin A.
abstract: The stoichiometry of Mn2+ binding to concanavalin A was found to be influenced by temperature, pH, and the presence or absence of saccharide. Demetalized concanavalin A binds one Mn2+ (S1 site) at 5 degrees C, pH 6.5, and two Mn2+ at 25 degrees C (S1 and S2 sites). The association constants for Mn2+ are 6.2 x 10(5) and 3.7 x 10(4) M-1 for the S1 and S2 sites, respectively, at 25 degrees C. Concanavalin A with one Mn2+ bound per monomer remains in an open conformation and exhibits a relatively high water proton relaxation rate. Concanavalin A with two Mn2+ ions remains in a closed conformation characterized by a lower relaxation rate. The rate of binding of the second Mn2+ to concanavalin A as determined by ESR and the rate of conversion of open form to closed form (folding over) as determined by proton relaxation rate measurements gave an identical rate constant of 80.0 +/- 5.8 M-1 h-1 at 17 degrees C. Ca2+, Sr2+, and high levels of methyl alpha-D-mannopyranoside also induce folding of concanavalin A. Ca2+ is not catalytic but stoichiometric in causing the folding. Mn2+ in the S1 site can be displaced by Ni2+, Co2+, and Zn2+, and Mn2+ in the S2 site can be displaced by Ca2+ and Sr2+. Concanavalin A with Ni2+, Co2+, Zn2+, or Mn2+ in the S1 site and Ca2+ or Sr2+ in the S2 site has a higher affinity for methylumbelliferyl alpha-D-mannopyranoside than Ni-Mn-, Co-Mn-, Zn-Mn-, and Cd-Cd-concanavalin A.
authors.affiliation: Biochemistry/Biophysics Program, Washington State University, Pullman 99164-4660.
authors.forename: A
authors.initials: A
authors.lastname: Sadhu
authors.forename: J A
authors.initials: JA
authors.lastname: Magnuson
mesh_terms: D001665:Binding Sites; D002241:Carbohydrates; D002413:Cations, Divalent; D003208:Concanavalin A; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008345:Manganese; D008670:Metals; D008968:Molecular Conformation
chemical_list: D002241:Carbohydrates; D002413:Cations, Divalent; D008670:Metals; D003208:Concanavalin A; D008345:Manganese