Comparison of the Effects of Saccharide Binding and Crystallization on the Zinc Transition-Metal Site of Concanavalin A

The Zn site in concanavalin A solution was studied by X-ray absorption fine structure spectroscopy (XAFS) with and without the saccharide methyl α-D-glucoside (aMG) bound to the protein. No structural change occurs in the metal-binding site when the saccharide is bound to the protein. There is, however, evidence for structural change remote from the metal site. This is in contrast to the significant changes that we have previously found to occur in the near neighborhood of the Zn atom when an aqueous solution of Zn concanavalin A crystallizes. We propose a structural explanation of these facts based on the known crystal structure of concanavalin A.