Mescher M F, Strominger J L
J Biol Chem. 1976 Apr 10;251(7):2005-14.
The glycoprotein which accounts for approximately 50% of the protein and all of the nonlipid carbohydrate of the cell envelope of Halobacterium salinarium (Mescher, M. F., Strominger, J. L., and Watson S. W. (1974) J. Bacteriol. 120, 945-954) has been purified and partially characterized. The glycoprotein has an apparent molecular weight of 200,000, is extremely acidic, and has a carbohydrate content of approximately 10 to 12%. The carbohydrate included neutral hexoses, amino sugar, and uronic acid. Information regarding the number, composition, and mode of attachment of the carbohydrate chains was obtained by isolation and examination of the glycopeptides derived from degradation of cell envelope protein with trypsin and pronase. Trypsin digestion resulted in two glycopeptides. One of these was large (approximately 55,000 daltons) and had most of the neutral hexose linked to it. The carbohydrate moieties consisted of di- and trisaccharides of glucosylgalactose and (uronic acid, glucose)-galactose attached via O-glycosidic linkages between galactose and threonine. The other tryptic glycopeptide had a relatively large heterosaccharide attached to it via an alkaline-stable linkage. The heterosaccharide contained 1 glucose, 8 to 9 galactose, 1 mannose, and 10 to 11 glucosamine residues, and approximately 6 residues of an unidentified amino augar. The alkaline stability of the linkage and the amino acid composition of glycopeptides resulting from Pronase digestion of the tryptic glycopeptide showed that the heterosaccharide was attached to an asparagine residue, presumably via an N-glycosylamine bond to the amide group. The intact glycoprotein has a single N-linked heterosaccharide, 22 to 24 O-linked disaccharides, and 12 to 14 O-linked trisaccharides per molecule. N- and O-glycosidic linkages are the most common carbohydrate-protein linkages in mammalian glycoproteins but, to our knowledge, this is the first report of either type of linkage in a prokaryotic cell envelope protein.
盐生盐杆菌（Mescher, M. F., Strominger, J. L., and Watson S. W. (1974) J. Bacteriol. 120, 945 - 954）细胞膜中的糖蛋白已被纯化并进行了部分特性鉴定，该糖蛋白约占细胞膜蛋白质的50%以及所有非脂质碳水化合物。该糖蛋白的表观分子量为200,000，酸性极强，碳水化合物含量约为10%至12%。碳水化合物包括中性己糖、氨基糖和糖醛酸。通过分离和检测用胰蛋白酶和链霉蛋白酶降解细胞膜蛋白产生的糖肽，获得了有关碳水化合物链的数量、组成和连接方式的信息。胰蛋白酶消化产生了两种糖肽。其中一种较大（约55,000道尔顿），大部分中性己糖与之相连。碳水化合物部分由通过半乳糖和苏氨酸之间的O - 糖苷键连接的葡萄糖基半乳糖二糖和三糖以及（糖醛酸、葡萄糖） - 半乳糖组成。另一种胰蛋白酶糖肽通过一种对碱稳定的连接键连接有一个相对较大的杂糖。该杂糖含有1个葡萄糖、8至9个半乳糖、1个甘露糖和10至11个葡糖胺残基，以及约6个未鉴定的氨基糖残基。链霉蛋白酶消化胰蛋白酶糖肽产生的糖肽的连接键的碱稳定性和氨基酸组成表明，该杂糖可能通过N - 糖基胺键与酰胺基团连接到天冬酰胺残基上。完整的糖蛋白每分子有一个N - 连接的杂糖、22至24个O - 连接的二糖和12至14个O - 连接的三糖。N - 和O - 糖苷键是哺乳动物糖蛋白中最常见的碳水化合物 - 蛋白质连接键，但据我们所知，这是原核细胞膜蛋白中这两种连接键类型的首次报道。
