Molecular dynamics of sugars bound to wheat germ agglutinin, as studied by deuterium nuclear magnetic resonance

Deuterium nuclear magnetic resonance is used to delineate the molecular dynamics of sugars bound to a lectin. 2H spin-spin relaxation times (from linewidth measurements) and reorientational correlation times are determined for N-acetylglucosamine specifically-labeled with 2H in the N-acetyl group and at carbon-3 of the pyranoside ring, in the presence and absence of wheat germ agglutinin. The correlation time for the 2H-label of N-acetylglucosamine-3-2H in the bound state is the same as that of the protein (3 X 10(-8)S), indicating that the six-membered ring has negligible motional freedom relative to the protein. The correlation time for the C2H3 group of N-acetyl-2H3-glucosamine (1.7 X 10(-9)S) shows that the N-acetyl side chain is also immobilized in the binding site, the only motion available being rotation of the C2H3 group about its threefold axis.