Amylosucrase, a Glucan-synthesizing Enzyme from the α-Amylase Family*
Amylosucrase, a Glucan-synthesizing Enzyme from the α-Amylase Family*
复制标题
DOI：
10.1074/jbc.m010998200
复制
发表时间：
2001-07
期刊：
影响因子：
--
通讯作者：
L. Skov;O. Mirza;A. Henriksen;Gabrielle Potocki De Montalk;M. Remaud-Siméon;P. Sarçabal;R. Willemot;P. Monsan;M. Gajhede
中科院分区：
文献类型：
--
作者：
L. Skov;O. Mirza;A. Henriksen;Gabrielle Potocki De Montalk;M. Remaud-Siméon;P. Sarçabal;R. Willemot;P. Monsan;M. Gajhede
淀粉蔗糖酶（E.C. 2.4.1.4）是糖苷水解酶（α-淀粉酶）家族13的成员，尽管其生物学功能是从蔗糖合成直链淀粉样聚合物。多糖奈瑟氏菌淀粉蔗糖酶的结构可分为5个结构域：N端为全螺旋结构域，（β/α）8桶A结构域，B和B′结构域，C端为8链β折叠结构域。与在大裂缝底部具有活性位点的其他家族13水解酶相比，淀粉蔗糖酶的活性位点在分子表面的口袋底部。在淀粉蔗糖酶中没有发现类似淀粉酶2亚位点的底物结合位点。该位点被（β/α）8-桶的第二个和第八个环中残基之间的盐桥阻断。结果是一种外作用酶。与其他水解酶中发现的环结构相比，淀粉蔗糖酶桶中的环7被延长，并且这种插入（形成结构域B′）被认为对于该酶的聚合物合成酶活性是重要的。B′-结构域的拓扑结构在分子表面上产生了一个具有几个沟壑的活性位点入口，可以被必须进出活性位点口袋的底物/产物（蔗糖、葡聚糖聚合物和果糖）特异性地使用。
Amylosucrase (E.C. 2.4.1.4) is a member of Family 13 of the glycoside hydrolases (the α-amylases), although its biological function is the synthesis of amylose-like polymers from sucrose. The structure of amylosucrase from Neisseria polysaccharea is divided into five domains: an all helical N-terminal domain that is not similar to any known fold, a (β/α)8-barrel A-domain, B- and B′-domains displaying α/β-structure, and a C-terminal eight-stranded β-sheet domain. In contrast to other Family 13 hydrolases that have the active site in the bottom of a large cleft, the active site of amylosucrase is at the bottom of a pocket at the molecular surface. A substrate binding site resembling the amylase 2 subsite is not found in amylosucrase. The site is blocked by a salt bridge between residues in the second and eight loops of the (β/α)8-barrel. The result is an exo-acting enzyme. Loop 7 in the amylosucrase barrel is prolonged compared with the loop structure found in other hydrolases, and this insertion (forming domain B′) is suggested to be important for the polymer synthase activity of the enzyme. The topology of the B′-domain creates an active site entrance with several ravines in the molecular surface that could be used specifically by the substrates/products (sucrose, glucan polymer, and fructose) that have to get in and out of the active site pocket.