GEOMETRICAL AND CONFORMATIONAL PROPERTIES OF GANGLIOSIDE GALNAC-G(D1A), IV(4)GALNACIV(3)NEU5ACII(3)NEU5ACGGOSE(4)CER

The aggregative properties of GalNAc-G(D1a) ganglioside, in comparison with those of G(D1a), have been investigated and correlated to the intrinsic conformation and mobility of the oligosaccharide chain of the molecules. Micellar parameters in aqueous solution (molecular mass, hydrodynamic radius as well as the surface area at the lipid/water interface and the packing parameter of the monomer inserted in the aggregate) are measured by the laser light-scattering technique. The presence of a further GalNAc residue causes a 22% increase in molecular mass, contrary to expectation. Oligosaccharide moiety three-dimensional structures have been modeled using molecular mechanics and dynamics calculations, based on NOE interactions observed for native gangliosides dissolved in deuterated dimethylsulfoxide or, as mixed micelles with fully deuterated dodecylphosphocholine, in D2O. Compared with G(D1A) the GalNAc-G(D1a) is less mobile, thus influencing the surface area, this lower mobility together with the GalNAc-G(D1a) conformation leads to a larger number of monomers participating in the formation of the micelle. The results further substantiate the model in which the three-dimensional structure and the intrinsic dynamic properties of the oligosaccharide chain affect the geometrical properties of the aggregate.