Chou M Y, Li S C, Kiso M, Hasegawa A, Li Y T
Department of Biochemistry, Tulane University, School of Medicine, New Orleans, Louisiana 70112.
J Biol Chem. 1994 Jul 22;269(29):18821-6.
Sialidase L releases 2,7-anhydro-NeuAc from sialoglycoconjugates (Li, Y.-T., Nakagawa, H., Ross, S. A., Hansson, G., and Li, S.-C. (1990) J. Biol. Chem. 265, 21629-21633). This enzyme has been purified more than 10,000-fold from Macrobdella leech. The final preparation gives a single protein band on SDS-polyacrylamide gel electrophoresis with the molecular mass of 84 kDa. The pI is determined to be 6.0 using isoelectric focusing. With 4-methylumbelliferyl-alpha-NeuAc as substrate, the pH optimum is between pH 5.5-7.0. Unlike regular sialidases, sialidase L is not inhibited by 2-deoxy-2,3-dehydro-NeuAc. Two of the seven tryptic peptides derived from sialidase L contain the consensus repeat S-X-D-X-G-X-T-W that has been found in the regular sialidases. Among various sialoglycoconjugates tested, sialidase L cleaves only the NeuAc alpha 2-->3Gal linkage. NeuAc alpha 2-->6Gal, NeuAc alpha 2-->6GalNAc, NeuAc alpha 2-->6GlcNAc, NeuAc alpha 2-->8-NeuAc, and NeuAc alpha 2-->9NeuAc linkages are not hydrolyzed. At pH 7.0, sialidase L and Clostridial sialidase release 46 and 92% of sialic acid, respectively, from bovine fetuin, indicating that sialidase L selectively cleaves NeuAc alpha 2-->3Gal linkages in fetuin. Sialidase L is the first sialidase found to exhibit a strict specificity toward the hydrolysis of the NeuAc alpha 2-->3Gal linkage, and it should become useful for the selective cleavage of NeuAc alpha 2-->3Gal linkages in sialoglycoconjugates without destroying other sialosyl linkages.
唾液酸酶L可从唾液酸糖缀合物中释放出2,7-脱水神经氨酸（李，Y.-T.，中川，H.，罗斯，S.A.，汉森，G.，以及李，S.-C.（1990年）《生物化学杂志》265卷，21629 - 21633页）。这种酶已从蚂蟥中纯化了10000多倍。最终制剂在SDS - 聚丙烯酰胺凝胶电泳上呈现出一条单一的蛋白质条带，分子量为84 kDa。使用等电聚焦法测定其pI为6.0。以4 - 甲基伞形酮基 - α - 神经氨酸为底物时，最适pH在5.5 - 7.0之间。与常规唾液酸酶不同，唾液酸酶L不受2 - 脱氧 - 2,3 - 脱氢神经氨酸的抑制。源自唾液酸酶L的七条胰蛋白酶肽段中有两条含有在常规唾液酸酶中发现的共有重复序列S - X - D - X - G - X - T - W。在测试的各种唾液酸糖缀合物中，唾液酸酶L仅切割NeuAcα2→3Gal连接。NeuAcα2→6Gal、NeuAcα2→6GalNAc、NeuAcα2→6GlcNAc、NeuAcα2→8 - NeuAc以及NeuAcα2→9NeuAc连接均不被水解。在pH 7.0时，唾液酸酶L和梭菌属唾液酸酶分别从牛胎球蛋白中释放出46%和92%的唾液酸，这表明唾液酸酶L选择性地切割胎球蛋白中的NeuAcα2→3Gal连接。唾液酸酶L是首个被发现对NeuAcα2→3Gal连接的水解具有严格特异性的唾液酸酶，它对于选择性切割唾液酸糖缀合物中的NeuAcα2→3Gal连接而不破坏其他唾液酸基连接应该会很有用。
