Lau Edmond Y, Felton James S, Lightstone Felice C
Biosciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
Chem Res Toxicol. 2006 Sep;19(9):1182-90. doi: 10.1021/tx0600999.
A computational study was performed to better understand the differences between human arylamine N-acetyltransferase (NAT) 1 and 2. Homology models were constructed from available crystal structures, and comparisons of the active site residues 125, 127, and 129 for these two enzymes provide insight into observed substrate differences. The NAT2 model provided a basis for understanding how some of the common polymorphisms may affect the structure of this protein. Molecular dynamics simulations of the human NAT models and the template structure (NAT from Mycobacterium smegmatis) were performed and showed the models to be stable and reasonable. Docking studies of hydroxylated heterocyclic amines in the models of NAT1 and NAT2 probed the differences exhibited by these two proteins with mutagenic agents. The hydroxylated heterocyclic amines were only able to fit into the NAT2 active site, and an alternative binding site by the phosphate-binding loop was found using our models and will be discussed. Quantum mechanical calculations on the O-acetylation reaction of the hydroxylated heterocyclic amines N-OH MeIQx and N-OH PhIP show that the reaction coordinates differ for these two compounds, but the activation barrier separating the reactant from the product are both low. The results of this study suggest that common polymorphisms in human NAT2 are distant from the active site and are more likely to destabilize the enzyme than affect catalysis. Additionally, the quantum mechanical calculations show that the observed differences in mutagenic activity between N-OH MeIQx and N-OH PhIP are not related to their acetylation reaction with NAT.
进行了一项计算研究，以更好地理解人类芳胺N - 乙酰基转移酶（NAT）1和2之间的差异。根据现有的晶体结构构建了同源模型，对这两种酶的活性位点残基125、127和129进行比较，有助于深入了解观察到的底物差异。NAT2模型为理解一些常见多态性如何影响该蛋白质的结构提供了基础。对人类NAT模型和模板结构（耻垢分枝杆菌的NAT）进行了分子动力学模拟，结果表明这些模型是稳定且合理的。在NAT1和NAT2模型中对羟基化杂环胺进行对接研究，探究了这两种蛋白质与诱变剂之间表现出的差异。羟基化杂环胺只能进入NAT2活性位点，利用我们的模型发现了一个由磷酸结合环形成的替代结合位点，并将对此进行讨论。对羟基化杂环胺N - OH MeIQx和N - OH PhIP的O - 乙酰化反应进行量子力学计算表明，这两种化合物的反应坐标不同，但将反应物与产物分开的活化能垒都很低。这项研究的结果表明，人类NAT2中的常见多态性距离活性位点较远，更有可能使酶不稳定而不是影响催化作用。此外，量子力学计算表明，观察到的N - OH MeIQx和N - OH PhIP之间诱变活性的差异与其与NAT的乙酰化反应无关。
