New insights into the role of distal histidine flexibility in ligand stabilization of dehaloperoxidase-hemoglobin from Amphitrite ornata.
New insights into the role of distal histidine flexibility in ligand stabilization of dehaloperoxidase-hemoglobin from Amphitrite ornata.
复制标题
关于远端组氨酸灵活性在 Amphitrite ornata 脱卤过氧化物酶-血红蛋白配体稳定中的作用的新见解。
DOI：
10.1021/bi9020567
复制
发表时间：
2010
期刊：
影响因子：
2.9
通讯作者：
G. Smulevich
中科院分区：
文献类型：
--
作者：
F. Nicoletti;M. Thompson;B. Howes;S. Franzen;G. Smulevich
与肌红蛋白和过氧化物酶相比，目前的工作强调了远端组氨酸在控制脱氢过氧化物酶（DHP）中血红素配体结合方面所起的重要作用。在DHP中，远端组氨酸具有高度的流动性，并经历构象变化，使其处于阴离子配体和水的氢键距离内，在那里可以发生强氢键。室温下详细的共振拉曼（RR）分析表明，在5坐标和6坐标（aquo）高自旋形式之间存在平衡。在12k时，平衡向水合态转变。这两种形式与现有的x射线结构一致，其中封闭构象（His55位于远端口袋中并与远端水分子氢键成键）和开放溶剂暴露构象（His55从远端口袋中位移（5坐标形式））处于平衡状态。此外，在298和12 K下的拉曼数据与4-碘酚存在下DHP的EPR结果的比较突出了纯5坐标高自旋形式（开放构象）的形成。本文报道的数据支持His55在促进底物和抑制剂在酶功能调节中的相互作用中的作用，如前所述。室温下处于平衡状态的His55的两种构象提供了一定程度的控制，使得远端组氨酸既可以作为过氧化物酶机制中的酸碱催化剂，又可以作为外源血红素配体的稳定氨基酸。
The present work highlights the important role played by the distal histidine in controlling the binding of heme ligands in dehaloperoxidase (DHP) as compared to myoglobin and peroxidases. In DHP the distal histidine is highly mobile and undergoes a conformational change that places it within hydrogen-bonding distance of anionic ligands and water, where strong hydrogen bonding can occur. The detailed resonance Raman (RR) analysis at room temperature shows the presence of an equilibrium between a 5-coordinate and a 6-coordinate (aquo) high-spin form. The equilibrium shifts toward the aquo form at 12 K. These two forms are consistent with the existing X-ray structures where a closed conformation, with His55 positioned in the distal pocket and H-bonded with the distal water molecule (6-coordinate), and an open solvent-exposed conformation, with the His55 displaced from the distal pocket (5-coordinate form), are in equilibrium. Moreover, the comparison between the Raman data at 298 and 12 K and the results obtained by EPR of DHP in the presence of 4-iodophenol highlights the formation of a pure 5-coordinate high-spin form (open conformation). The data reported herein support the role of His55 in facilitating the interaction of substrate and inhibitor in the regulation of enzyme function, as previously suggested. The two conformations of His55 in equilibrium at room temperature provide a level of control that permits the distal histidine to act as both the acid-base catalyst in the peroxidase mechanism and the stabilizing amino acid for exogenous heme-coordinated ligands.