Binding of 13 C-Enriched α-Methyl-D-Glucopyranoside to Concanavalin A as Studied by Carbon Magnetic Resonance

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Abstract
Binding of alpha-methyl-D-glucopyranoside, uniformly enriched with 14% (13)C, to zinc and manganese derivatives of concanavalin A at pH 5.6 was studied by pulsed Fourier transform carbon magnetic resonance techniques. Spin-lattice relaxation (T(1)) of the [(13)C]carbons of the sugar was measured in the absence and presence of the two transition metal derivatives of the protein. In the presence of the manganese derivative of concanavalin A, selective relaxation of the sugar carbons was observed. The values for T(1) reflect different distances between the carbons of the bound sugar and the manganese ion. Calculation of the distance between the manganese ion and each carbon of the sugar permit the 3-dimensional orientation of the bound sugar to be determined relative to the transition metal site in the protein. The results indicate that alpha-methyl-D-glucopyranoside binds to the protein in the Cl chair conformation with its 3- and 4- carbons closest to the manganese ion at a mean distance of 10 A.