Transition state structure of arginine kinase: Implications for catalysis of bimolecular reactions
Transition state structure of arginine kinase: Implications for catalysis of bimolecular reactions
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DOI：
10.1073/pnas.95.15.8449
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发表时间：
1998-07-21
影响因子：
11.1
通讯作者：
Chapman, MS
中科院分区：
文献类型：
--
作者：
Zhou, GF;Somasundaram, T;Chapman, MS
精氨酸激酶属于酶家族，包括肌酸激酶，其在具有波动能量需求的细胞中催化ATP的缓冲，并且已经成为经典酶学研究的范例。本文报道的其过渡态类似物复合物的1.86埃分辨率结构，揭示了其活性位点，并为精确底物对齐在双分子反应催化中的重要性提供了直接证据，与以前研究的单分子反应相反，在本文研究的过渡态类似物复合物中，在ATP和精氨酸之间的缔合在线转移期间，硝酸盐模拟平面γ-磷酰基，活性位点未被扰动，并且反应物不像在双底物复合物中那样被共价约束，因此可以测量它们被酶预对准的精确程度。熵效应可能有助于催化作用，但孤对轨道也足够接近它们的最佳轨道，以使轨道转向成为亲核攻击期间的一个因素。结构表明，极化，应变过渡态，和酸碱催化也作出贡献，但是，在相反的单分子酶反应，它们的作用似乎是次要的底物对齐在这个双分子反应。
Arginine kinase belongs to the family of enzymes, including creatine kinase, that catalyze the buffering of ATP in cells with fluctuating energy requirements and that has been a paradigm for classical enzymological studies. The 1.86-Angstrom resolution structure of its transition-state analog complex, reported here, reveals its active site and offers direct evidence for the importance of precise substrate alignment in the catalysis of bimolecular reactions, in contrast to the unimolecular reactions studied previously, In the transition-state analog complex studied here, a nitrate mimics the planar gamma-phosphoryl during associative in-line transfer between ATP and arginine, The active site is unperturbed, and the reactants are not constrained covalently as in a bisubstrate complex, so it is possible to measure how precisely they are pre-aligned by the enzyme. Alignment is exquisite, Entropic effects may contribute to catalysis, but the lone-pair orbitals are also aligned close enough to their optimal trajectories for orbital steering to be a factor during nucleophilic attack. The structure suggests that polarization, strain toward the transition state, and acid-base catalysis also contribute, but, in contrast to unimolecular enzyme reactions, their role appears to be secondary to substrate alignment in this bimolecular reaction.