Low frequency spectral density of ferrous heme: Perturbations induced by axial Ligation and protein insertion
Low frequency spectral density of ferrous heme: Perturbations induced by axial Ligation and protein insertion
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DOI：
10.1529/biophysj.107.114736
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发表时间：
2007-12-15
影响因子：
3.4
通讯作者：
Champion, Paul M.
中科院分区：
文献类型：
--
作者：
Gruia, Flaviu;Ye, Xiong;Champion, Paul M.
飞秒相干光谱用于探测溶液中亚铁血红素基团的低频（20-400 cm（-1））模式，有和没有2-甲基咪唑（2 MeIm）作为轴向配体。将结果与血红素蛋白（CPO、P450（cam）、HRP、Mb）进行比较，其中血红素插入蛋白质导致低频谱密度的重新分布和相干信号的更长阻尼时间（类似于60%）。咪唑与亚铁血红素连接的主要作用是低频力常数的“软化”，其因子类似于0.6 +/- 0.1。评估了咪唑连接的功能后果，发现当咪唑被结合时，焓CO再结合屏障显着增加。力常数软化分析，结合动力学结果，表明铁被取代的情况下，从血红素平面的咪唑配体的情况下，只有类似于0.2埃，而它被取代的类似于0.4埃时，咪唑（组氨酸）存在。这表明咪唑（组氨酸）作为轴向配体的结合，以及伴随的力常数软化，导致血红素基团的非谐畸变，具有显着的功能后果。
Femtosecond coherence spectroscopy is used to probe low frequency (20-400 cm(-1)) modes of the ferrous heme group in solution, with and without 2-methyl imidazole (2MeIm) as an axial ligand. The results are compared to heme proteins (CPO, P450(cam), HRP, Mb) where insertion of the heme into the protein results in redistribution of the low frequency spectral density and in (similar to 60%) longer damping times for the coherent signals. The major effect of imidazole ligation to the ferrous heme is the "softening'' of the low frequency force constants by a factor of similar to 0.6 +/- 0.1. The functional consequences of imidazole ligation are assessed and it is found that the enthalpic CO rebinding barrier is increased significantly when imidazole is bound. The force constant softening analysis, combined with the kinetics results, indicates that the iron is displaced by only similar to 0.2 angstrom from the heme plane in the absence of the imidazole ligand, whereas it is displaced by similar to 0.4 angstrom when imidazole ( histidine) is present. This suggests that binding of imidazole ( histidine) as an axial ligand, and the concomitant softening of the force constants, leads to an anharmonic distortion of the heme group that has significant functional consequences.