Metal ion binding to concanavalin A.

ABSTRACT

Metal ion activation of saccharide binding has been studied for concanavalin A near pH 7.0. Although two metal ions, a transition metal ion and a Ca2+ ion, can bind, both are not required. Ca2+ alone, Mn2+ alone, or Ca2+ with other transition metal ions can activate this lectin. Only one Ca2+ ion per subunit or only one Mn2+ per subunit is sufficient. Metal ion binding was studied by magnetic resonance techniques and direct binding assays. Saccharide binding activity was monitored by following the fluorescence of 4-methylumbelliferyl a-D-mannopyranoside. When Ca2+ binds to demetalized concanavalin A, the transition metal ion site is hindered. When Mn2+ alone binds to demetalized concanavalin A, saccharide binding activity is induced. A subsequent conformational change, not necessary for carbohydrate binding activity, covers the Mn2+.