A model theoretical study on ligand exchange reactions of CooA
A model theoretical study on ligand exchange reactions of CooA
复制标题
CooA配体交换反应的模型理论研究
DOI：
10.1039/c3cp43253j
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
S. Aono
中科院分区：
文献类型：
--
作者：
T. Ishida;S. Aono
RR-CooA是一种一氧化碳敏感的血红素蛋白，其中CO与血红素基团的结合刺激了CooA的转录激活活性。在这个过程中，亚铁血红素经历了一系列的配体交换。在铁的形式中，血红素有Cys75和Pro2作为轴向配体。在还原的亚铁形式中，血红素具有His77而不是Cys75作为Pro2的轴向配体。只有在简化形式下，CooA才能结合取代Pro2的CO。对CooA的配体交换反应进行了模型计算。配位的脯氨酸是中性的质子化形式。半胱氨酸与组氨酸的配体交换是由一个相对较小的模型重现的。这种交换主要是由于铁态和亚铁态之间非键硫p轨道的稳定性不同所致。蛋白质中CO、NO和O2之间气体分子的选择性可以用RR-CooA产物的相对稳定性来解释。CH-CooA也是如此，在铁和亚铁状态下，N-末端的氨基和组氨酸都与铁离子配位。RR-CooA与气体分子结合的能力略强于CH-CooA。在RR-CooA的铁型中，血红素变形为褶皱形式，而铁型的血红素是平面的，这导致前者的Q带红移。
Rr-CooA is a CO-sensor heme protein, where binding of CO with the heme group stimulates a transcriptional activator activity of CooA. In this process, the heme undergoes a series of ligand exchanges. In the ferric form, the heme has Cys75 and Pro2 as the axial ligands. In the reduced ferrous form, the heme has His77 instead of Cys75 as an axial ligand with Pro2. Only in the reduced form, CooA can bind CO that replaces Pro2. Model calculations are carried out to elucidate the ligand exchange reactions of CooA. The coordinated proline is found to be the neutral, protonated form. The ligand exchange of cysteine for histidine is reproduced by a relatively small model. This exchange would be mainly due to difference in stability of the non-bonding sulfur p-orbital in Cys75 between the ferric and ferrous states. The selectivity of gas molecules among CO, NO, and O2 in the proteins is explained by the relative stability of products for Rr-CooA. This is also the case for Ch-CooA, where the amino group of the N-terminus and a histidine are coordinated to the iron ion both in the ferric and ferrous states. The ability to bind the gas molecules is a little stronger in Rr-CooA than in Ch-CooA. In the ferric form of Rr-CooA, heme is deformed to a ruffled form whereas heme is planar in the ferrous form, which leads to a red-shifted Q-band in the former.