3-DIMENSIONAL STRUCTURE OF A GLYCOSPHINGOLIPID HAVING A NOVEL CARBOHYDRATE LINKAGE, GAL-BETA-1-4(FUC-ALPHA-1-3)GLC-BETA-1-3GAL-BETA DETERMINED BY THEORETICAL CALCULATIONS

The novel glycosphingolipid, SEGLx (Gal beta 1-4(Fuc alpha 1-3)Glc bet a 1-3Gal beta Cer), which was identified by us (Kawakami Y, et al. (19 93) J Biochem 114:677-83), shows a characteristic spectrum on H-1-NMR analysis, in which the anomeric proton resonances of a reducing end ga lactose and a glucose are split. To elucidate the structural character istics of SEGLx, we determined its three-dimensional (3D) structure by means of computer simulation, involving such techniques as molecular mechanics (MM2), the semiempirical molecular orbital method (AM1), mol ecular dynamics (Amber), and computer 3D modelling. With the hypothesi s that all OH group(s) of a ceramide participate in intramolecular hyd rogen bonds, two kinds of stable conformers, horizontal and right-angl ed ones, were formed, depending on the ceramide species. The present f indings suggest that the chemical species of both the long chain base and fatty acid moieties, mainly the occurrence of OH group(s), affect the chemical shifts of the anomeric proton resonances not only of the reducing terminal galactose but also the penultimate glucose through t he formation of intramolecular hydrogen bonds. Computer simulation thr ough theoretical calculation and 3D modelling was shown to be the best means of confirming the results obtained by experimental analysis.