Binding of Imidazole to the Heme of Cytochrome c1 and Inhibition of the bc1 Complex from Rhodobacter sphaeroides I. EQUILIBRIUM AND MODELING STUDIES
Binding of Imidazole to the Heme of Cytochrome c1 and Inhibition of the bc1 Complex from Rhodobacter sphaeroides I. EQUILIBRIUM AND MODELING STUDIES
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DOI：
10.1074/jbc.m110.128058
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发表时间：
2010-07-16
影响因子：
4.8
通讯作者：
Wraight, Colin A.
中科院分区：
文献类型：
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作者：
Kokhan, Oleksandr;Shinkarev, Vladimir P.;Wraight, Colin A.
我们用咪唑（Im）和N-甲基咪唑（MeIm）作为探针，研究了洗涤剂增溶的类球红细菌（Rhodobacter sphaeroides）bc（1）复合物中细胞色素（cyt）c（1）的血红素结合腔。咪唑与细胞色素c1的结合大大降低了血红素的中点电位，并完全抑制了bc 1复合物的活性。温度依赖性表明，Im的结合（K-d约为330 μ M，25 ℃，pH 8）是由螺旋驱动的（Δ H-0 = -56 kJ/mol，Δ S-0 = -121 J/mol/K），而MeIm的结合弱30倍（K-d近似于9.3mM）并且是熵驱动的（Δ H-0 = 47 kJ/mol，Δ S-0度= 197 J/mol/K）。大的热力学和熵的贡献表明配体结合引起的cytc 1的结构和溶剂化的显著变化。将这些结果与先前获得的可溶性细胞色素c和c（2）的结果进行比较，表明Im与细胞色素c（1）的结合是通过血红素裂隙内氢键的形成来辅助的。这得到了细胞色素c、c2和c1的Im加合物的分子动力学模拟的有力支持，该模拟显示Im的N δ H与细胞色素c（1）蛋白质之间形成氢键，或者与血红素裂隙中的配体螯合的水分子形成氢键。
We have used imidazole (Im) and N-methylimidazole (MeIm) as probes of the heme-binding cavity of membrane-bound cytochrome (cyt) c(1) in detergent-solubilized bc(1) complex from Rhodobacter sphaeroides. Imidazole binding to cyt c1 substantially lowers the midpoint potential of the heme and fully inhibits bc1 complex activity. Temperature dependences showed that binding of Im (K-d approximate to 330 mu M, 25 degrees C, pH 8) is enthalpically driven (Delta H-0 = -56 kJ/mol, Delta S-0 = -121 J/mol/K), whereas binding of MeIm is 30 times weaker (K-d approximate to 9.3 mM) and is entropically driven (Delta H-0 = 47 kJ/mol, Delta S-0 degrees = 197 J/mol/K). The large enthalpic and entropic contributions suggest significant structural and solvation changes in cyt c1 triggered by ligand binding. Comparison of these results with those obtained previously for soluble cyts c and c(2) suggested that Im binding to cyt c(1) is assisted by formation of hydrogen bonds within the heme cleft. This was strongly supported by molecular dynamics simulations of Im adducts of cyts c, c2, and c1, which showed hydrogen bonds formed between the N delta H of Im and the cyt c(1) protein, or with a water molecule sequestered with the ligand in the heme cleft.