Structural studies on a binding site for Dolichos biflorus agglutinin in the small intestine of the mouse

Glycoproteins which bound to Dolichos biflorus agglutinin (DBA) were isolated from the small intestine of 129/Sv mice. Among oligosaccharides released from the carbohydrate moieties of the glycoproteins by endo-beta-galactosidase, the major one with N-acetylgalactosamine at the non-reducing end was isolated by QAE-Sephadex A-25 column chromatography. The structure of the oligosaccharide was elucidated to be GalNAc beta 1----4(NeuAc alpha 2----3)Gal beta 1----4GlcNAc beta 1----3Gal by compositional analysis, methylation analysis before and after mild acid hydrolysis, sequential glycosidase digestion, secondary ion mass spectrometry (SIMS), and nuclear magnetic resonance spectroscopy. The SIMS signal of m/z 1,071 was consistent with the presence of the branched sequence, GalNAc(NeuAc)GalGlcNAc, and the signal was also detected in the high-molecular-weight fraction obtained after endo-beta-galactosidase digestion. The pentasaccharide identified here has the terminal structure of ganglioside GM2, and an apparently identical one has been identified as the epitope of blood group Sda and the DBA binding site in human T-H urinary glycoprotein. Thus, the present result has extended our knowledge of the biological meaning of the oligosaccharide structure and has established that GalNAc beta 1----4(NeuAc alpha 2----3)Gal beta 1----4GlcNAc is a DBA binding site in the small intestine of the mouse.