A structural view of the action of Escherichia coli (lacZ) β-galactosidase
A structural view of the action of Escherichia coli (lacZ) β-galactosidase
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DOI：
10.1021/bi011727i
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发表时间：
2001-12-11
期刊：
影响因子：
2.9
通讯作者：
Matthews, BW
中科院分区：
文献类型：
--
作者：
Juers, DH;Heightman, TD;Matthews, BW
给出了一系列用于模拟β-半乳糖苷酶反应坐标中间体的复合体的结构。这些络合物澄清并加强了先前关于催化机理的建议。亲核剂Glu537被认为与半乳糖部分共价结合。在两种潜在的酸，镁和Glu461中，后者处于更好的位置，直接帮助离开基团，这表明金属离子起到了次要作用。钠离子通过直接连接半乳糖6-羟基参与底物结合。所提出的反应坐标涉及半乳糖部分深入活性中心口袋的移动。对于那些确实与Dee结合的配体，有一个相关的构象变化，其中794-804环中的残基向结合位置移动了10埃。在某些情况下，这可以通过结合额外的配体来抑制。由此产生的对中间体的访问受限有助于解释为什么乳胶操纵子的天然诱导剂别乳糖是转糖基化的首选产物。
The structures of a series of complexes designed to mimic intermediates along the reaction coordinate for beta -galactosidase are presented. These complexes clarify and enhance previous proposals regarding the catalytic mechanism. The nucleophile, Glu537, is seen to covalently bind to the galactosyl moiety. Of the two potential acids, Mg2+ and Glu461, the latter is in better position to directly assist in leaving group departure, suggesting that the metal ion acts in a secondary role. A sodium ion plays, a part in substrate binding by directly ligating the galactosyl 6-hydroxyl. The proposed reaction coordinate involves the movement of the galactosyl moiety deep into the active site pocket. For those ligands that do bind dee ly there is an associated conformational change in which residues within loop 794-804 move up to 10 Angstrom closer to the site of binding. In some cases this can be inhibited by the binding of additional Ligands. The resulting restricted access to the intermediate helps to explain why allolactose, the natural inducer for the lac operon, is the preferred product of transglycosylation.