Luo Y, Li S C, Li Y T, Luo M
Center for Macromolecular Crystallography, University of Alabama at Birmingham, AL, 35294, USA.
J Mol Biol. 1999 Jan 8;285(1):323-32. doi: 10.1006/jmbi.1998.2345.
Intramolecular trans-sialidase from leech (Macrobdella decora) is the first member of the sialidase superfamily found to exhibit strict specificity towards the cleavage of terminal Neu5Acalpha2-->3Gal linkage in sialoglycoconjugates. Its release of 2,7-anhydro-Neu5Ac instead of Neu5Ac indicates that it catalyzes an intramolecular trans-sialosyl reaction. Crystal structures of its complexes with an inactive substrate analogue 2-propenyl-Neu5Ac, and with the product 2,7-anhydro-Neu5Ac, have been determined to 1.8 A resolution. The boat conformation of the pyranose observed in the complexes supports the proposed enzymatic mechanism that O7 of an axial 6-glycerol group attacks the positively charged C2 of the intermediate. A generalized mechanism is proposed for the sialidase superfamily.
来自水蛭（装饰巨蛭）的分子内反式唾液酸酶是唾液酸酶超家族中首个被发现对唾液酸糖缀合物中末端Neu5Acα2→3Gal连接的切割表现出严格特异性的成员。它释放出2,7-脱水-Neu5Ac而非Neu5Ac，这表明它催化了分子内反式唾液酸基反应。已确定其与无活性底物类似物2-丙烯基-Neu5Ac以及产物2,7-脱水-Neu5Ac形成的复合物的晶体结构，分辨率达到1.8 Å。在复合物中观察到的吡喃糖的船式构象支持了所提出的酶促机制，即轴向6-甘油基团的O7攻击中间体带正电荷的C2。为唾液酸酶超家族提出了一种通用机制。
