北大生物化学完整chapter9分析.pptVIP

Selectins: a family of lectins, found in plasma membranes, that mediate cell-cell recognition and adhesion. Role of lectin-ligand interactions in lymphocyte movement to the site of an infection or injury Helicobacter pylori cells adhering to the gastric surface causes ulcers by interactions between a bacterial surface lectin and the Leb oligosaccharide (a blood group antigen) of the gastric epithelium Lectin-Carbohydrate Interaction- very strong highly specific Neu5Ac (N-acetylneuraminic acid) binding site mannose 6P Ca 2+ Sialic acid-specific lectin Mannose 6P receptor Roles of oligosaccharides in recognition and adhesion at the cell surface Working with carbohydrates Analyze composition of monosaccharides (high-performance liquid chromatography, HPLC or gas-liquid chromatography ) Determination of position(s) of glycosidic bonds Methylate free hydroxyl group (-OH) by CH3I, then hydrolyze the methylated polysaccharide in acid. The only free -OH(s) present in the monosaccharide are those involved in glycosidic bonds Determination of sequence of monosaccharides Mass spectrometry and NMR spectroscopy MALDI-TOF spectrometry Enzymatic hydrolysis with specific glycosidase peptide N-glycosidase F neuraminidase peptide N-glycosidase F neuraminidase b-1,4-galactosidase Summary Sugars are compounds containing an aldehyde or ketone group and two or more hydroxyl groups; Monosaccharides generally contain several chiral carbons and therefore exist in a variety of stereochemical forms; Monosaccharides commonly form internal hemiacetals or hemiketals; A hydroxy group of one monosaccharide can add to the anomeric carbon of a second monosaccharide to form an acetal. In this disaccharide, the glycosidic bond protects the anomeric carbon from oxidation; Oligosaccharides are short polymers of several monosaccharides joined by glycosidic bonds; The common nomenclature for di-