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糖蛋白是指含糖量低于4%的一类结合蛋白质。其糖的组成部分通常是多个由12～15个单糖残基或其衍生物组成的低(寡)聚糖链。低聚糖链与蛋白质部分借N-β-糖苷键与多肽链中的天门冬酰胺残基的酰胺N原子共价结合或借O-α-糖苷键与多肽链中的苏氨酸残基或丝氨酸残基抑或是与5-羟基赖氨酸残基或羟脯氨酸残基的羟基共价结合。有的还可借S-糖苷键与多肽链中半胱氨酸的巯基共价结合。位于细胞表面的糖蛋白的低聚糖链与其表面上的糖脂低聚糖链一起分布在细胞外表面上,构
A glycoprotein is a type of bound protein that contains less than 4% sugar. The constituents of its sugar are usually a plurality of low (oligo)glycan chains composed of 12 to 15 monosaccharide residues or derivatives thereof. The oligosaccharide chain and the protein moiety are covalently bonded via an N-β-glycosidic bond to the amide N atom of the asparagine residue in the polypeptide chain or via an O-α-glycosidic bond to a threonine residue in the polypeptide chain The serine residue is either covalently bound to the hydroxyl group of the 5-hydroxylysine residue or the hydroxyproline residue. Some may also be covalently bound to the sulfhydryl group of a cysteine in the polypeptide chain by an S-glycosidic bond. The oligosaccharide chain of the glycoprotein located on the cell surface is distributed on the outer surface of the cell together with the glycolipid oligosaccharide chain on the surface of the cell.