STRUCTURE AND DYNAMICS OF THE SIALIC-ACID MOIETY OF G(M3)-GANGLIOSIDEAT THE SURFACE OF A MAGNETICALLY ORIENTED MEMBRANE

C-13-NMR techniques in oriented bilayer systems composed of DMPC and C HAPSO have been used to measure dipolar interactions between C-13-C-13 and C-13-H-1 pairs located in the sialic acid moiety of ganglioside G (M)3. These interactions are reduced to a structural and motional mode l for the headgroup of this glycolipid using an order matrix approach. The analysis shows an average structure possessing a high degree of o rder and is most consistent with structures that are well extended fro m the membrane surface. Saturation of the ganglioside environment with high concentrations of Ca2+ (0.28 M) produces a small perturbation of the head group. G(M)3 dissolved in a DMPC/CHAPSO system can also be d emonstrated to bind wheat germ agglutinin (WGA). The minimal perturbat ion of structure-dependent parameters suggests that the dominant struc ture of the sialic acid moiety in the isolated membrane system is favo red for binding by the protein.