Tertiary Structure of Ganglioside GA1 as Determined by NMR Spectroscopy

摘要

Investigation of the structure of the gangliosides has proven to be very important in the understanding of their biological roles. We have determined the tertiary structure of asialoganglioside GM1 (GA1) using NMR spectroscopy and distance geometry calculations. All of the structures are very similar except the glycosidic torsion angles in the ring IV and ring III linkages. There are two low-energy structures for GA1, G1 and G2. G1 differs from G2 only in the IV-III glycosidic linkages and the orientation of acetamido group in ring III. There is a stable intramolecular hydrogen bond between the third hydroxyl group in ring I and the ring oxygen atom in ring II. Also, there may be a weak hydrogen bond between the second hydroxyl group in ring IV and the acetamido group in ring III. Small coupling constants of 3JIH3,IOH3 and 3JIVH2,IVOH2 support this result. Overall structural features of GA1 are very similar to those of GM1. It implicates that specificities of the sugar moieties in GM1 are caused not by their tertiary foldings, but mainly by the electrostatic interactions between the polar sialic acid and its receptors. Since it is evident that GA1 is more hydrophobic than GM1, a receptor with a hydrophobic binding site can recognize the GA1 better than GM1. Studies on the conformational properties of GA1 may lead to a better understanding of the molecular basis of its functions.