Multiconformation continuum electrostatics analysis of the effects of a buried Asp introduced near heme a in Rhodobacter sphaeroides cytochrome c oxidase.
Multiconformation continuum electrostatics analysis of the effects of a buried Asp introduced near heme a in Rhodobacter sphaeroides cytochrome c oxidase.
复制标题
对球形红细菌细胞色素 c 氧化酶中血红素 a 附近引入的埋藏天冬氨酸的影响进行多构象连续静电分析。
DOI：
10.1021/bi100663u
复制
发表时间：
2010
期刊：
影响因子：
2.9
通讯作者：
Gunner,MR
中科院分区：
文献类型：
--
作者：
Zhang,Jun;Gunner,MR
细胞色素氧化酶 (CcO) 通过一系列质子耦合电子转移将 O2 还原为水，产生跨膜电化学梯度。耦合电子和质子转移需要在反应循环的每个阶段改变埋入残基的 pKa 值。 Hemeai 是 CcO 电子转移链中的关键辅助因子。 Ser44 突变为 Asp 已有报道 [Mills, D. A., et al. (2008)Biochemistry 47, 11499−11509]，改变了球形红细菌CcO中的半轴配体His102的氢键受体。这会在 CcO 内部添加酸性残基。使用连续静电程序 MCCE 比较了野生型血红素和 S44D CcO 的电化学行为。仅当附近的血红素被氧化时，引入的深埋天冬氨酸在生理 pH 值下仍保持电离状态。现在计算出 Hemereduction 与 Asp 质子结合强耦合，而对于 Ser44，它与多个位点的小质子化位移弱耦合，增加了突变体的 pH 依赖性。在 pH 7 时，部分电离的 Asp 44 经计算可将血红素氧化还原电位降低 50 mV，正如考虑到耦合电子和质子转移的热力学所预期的那样。这突显了实验结果中的一个奇怪的发现，即发现了低 Asp pKa 和稳定的还原血红素。通过连续静电学和密度泛函理论计算的轴向组氨酸配体氢键对模型复合物中血红素氧化的稳定作用非常一致。
Cytochromecoxidase (CcO) reduces O2to water via a series of proton-coupled electron transfers, generating a transmembrane electrochemical gradient. Coupling electron and proton transfer requires changing the pKavalues of buried residues at each stage in the reaction cycle. Hemeais a key cofactor in the CcO electron transfer chain. Mutation of Ser44 to Asp has been reported [Mills, D. A., et al. (2008)Biochemistry 47, 11499−11509], changing the hydrogen bond acceptor from His102, the hemeaaxial ligand inRhodobactor sphaeroidesCcO. This adds an acidic residue to the CcO interior. The electrochemical behavior of hemeain wild-type and S44D CcO is compared using the continuum electrostatics program MCCE. The introduced, deeply buried Asp remains ionized at physiological pH only when the nearby heme is oxidized. Hemeareduction is now calculated to be strongly coupled to Asp proton binding, while with Ser44, it is weakly coupled to small protonation shifts at multiple sites, increasing the pH dependence in the mutant. At pH 7, the partially ionized Asp 44 is calculated to lower the heme redox potential by 50 mV as expected given the thermodynamics of coupled electron and proton transfers. This highlights an curious finding in the experimental results where a low Asp pKais found together with a stabilized reduced heme. The stabilization of a heme oxidation in a model complex by a hydrogen bond to the axial His ligand calculated with continuum electrostatics and with density functional theory were in good agreement.