Sulfotransferase 1A1 Substrate Selectivity: A Molecular Clamp Mechanism.
Sulfotransferase 1A1 Substrate Selectivity: A Molecular Clamp Mechanism.
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DOI：
10.1021/acs.biochem.5b00406
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发表时间：
2015-10-06
期刊：
影响因子：
2.9
通讯作者：
Leyh TS
中科院分区：
文献类型：
--
作者：
Cook I;Wang T;Leyh TS
人的胞液硫转移酶(SOLT)通过将硫酰基团(−-SO3)从PAP(3‘-磷酸腺苷-5’-磷酸-硫酸盐)转移到受体的羟基和伯胺，调节数百，甚至数千种小分子代谢物和外源物质。在富含SULT1A1的肝脏中，SULT1A1参与修饰代谢物和中和毒素。1A1的特异性是所有结果中最广泛的，了解其选择性是了解其生物学的基础。在这里，我们第一次证明了SULT1A1底物自然地分为两类：那些亲和力要么增强了~20倍(正协同作用)，要么不受饱和核苷酸存在影响(中性协同作用)。正协同底物的催化效率(kcat/Km)约为中性协同化合物的100倍；因此，正协同的催化效率(kcat/Km)约高3个数量级。全原子动力学模拟为这些观察提出了一种分子机制，其中只有正协同化合物的结合导致两个苯丙氨酸残基(F81和84)重新定位并“夹心”底物的酚性部分，从而增强底物亲和力并定位亲核氧以备攻击。分子动力学电影显示，中性-协同作用的化合物在活性中心“游荡”，很少达到反应位置。对选择的点突变的深入分析有力地支持了这一模型，并提供了活性位点亚段相互依赖的催化功能的密切视图。
The human cytosolic sulfotransferases (SULTs) regulate hundreds, perhaps thousands, of small molecule metabolites and xenobiotics via transfer of a sulfuryl moiety (−SO3) from PAPS (3′-phosphoadenosine 5′-phosphosulfate) to the hydroxyls and primary amines of the recipients. In liver, where it is abundant, SULT1A1 engages in modifying metabolites and neutralizing toxins. The specificity of 1A1 is the broadest of any SULT, and understanding its selectivity is fundamental to understanding its biology. Here, for the first time, we show that SULT1A1 substrates separate naturally into two classes: those whose affinities are either enhanced ~20-fold (positive synergy) or unaffected (neutral synergy) by the presence of a saturating nucleotide. kcat for the positive-synergy substrates is shown to be ~100-fold greater than that of neutral-synergy compounds; consequently, the catalytic efficiency (kcat/Km) is approximately 3 orders of magnitude greater for the positive-synergy species. All-atom dynamics modeling suggests a molecular mechanism for these observations in which the binding of only positive-synergy compounds causes two phenylalanine residues (F81 and 84) to reposition and “sandwich” the phenolic moiety of the substrates, thus enhancing substrate affinity and positioning the nucleophilic oxygen for attack. Molecular dynamics movies reveal that the neutral-synergy compounds “wander” about the active site, infrequently achieving a reactive position. In-depth analysis of select point mutants strongly supports the model and provides an intimate view of the interdependent catalytic functions of subsections of the active site.