Coherence spectroscopy investigations of the low-frequency vibrations of heme: Effects of protein-specific perturbations
Coherence spectroscopy investigations of the low-frequency vibrations of heme: Effects of protein-specific perturbations
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DOI：
10.1021/ja7104027
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发表时间：
2008-04-16
影响因子：
15
通讯作者：
Champion, Paul M.
中科院分区：
文献类型：
--
作者：
Gruia, Flaviu;Kubo, Minoru;Champion, Paul M.
利用飞秒相干光谱技术研究了血红素蛋白在溶液中的低频(20-200 cm(-1))振动模式。比较了辣根过氧化物酶(HRP)、肌红蛋白(Mb)和空肠弯曲菌珠蛋白(CGB)在相干光谱中的差异。结果表明，氢键和配基电荷对低频相干谱的影响不大，血红素基团的蛋白质特异性变形降低了其对称性，控制了相对光谱强度。这种变形可能为蛋白质提供了一种调整血红素反应坐标的方法，这样它们就可以执行一系列广泛的特定功能。天然HRP在50 cm(-1)以上表现出复杂的光谱行为，在50 cm(-1)以下表现出很弱的活性。底物类似物苯异羟肟酸的结合导致HRP的相干光谱和拉曼光谱发生明显变化，这与血红素水配体的稳定一致。在均一的血红素配位和自旋态的条件下，对这三种蛋白质的CN衍生物进行了比较。在X射线结构中，MbCN在40 cm(-1)附近以穹顶模式为主，而HRPCN在较高频率(96 cm(-1))表现出较强的振荡，这与观测到的鞍形变有关。相比之下，CgbCN显示的低频相干光谱包含30和80厘米(-1)附近的强模式，可能与血红素穹顶和褶皱的组合有关。HRPNO在光解激活的40 cm(-1)附近有一个较强的穹顶模式。当蛋白质材料屏蔽了血红素的溶剂波动时，相干运动的衰减显著降低，当T小于或类似于50K时，进一步减小，因为蛋白质-溶剂声子浴导致的纯脱相过程被冻结。
Femtosecond coherence spectroscopy is used to probe the low-frequency (20-200 cm(-1)) vibrational modes of heme proteins in solution. Horseradish peroxidase (HRP), myoglobin (Mb), and Campylobacter jejuni globin (Cgb) are compared and significant differences in the coherence spectra are revealed. It is concluded that hydrogen bonding and ligand charge do not strongly affect the low-frequency coherence spectra and that protein-specific deformations of the heme group lower its symmetry and control the relative spectral intensities. Such deformations potentially provide a means for proteins to tune heme reaction coordinates, so that they can perform a broad array of specific functions. Native HRP displays complex spectral behavior above similar to 50 cm(-1) and very weak activity below similar to 50 cm(-1). Binding of the substrate analog, benzhydroxamic acid, leads to distinct changes in the coherence and Raman spectra of HRP that are consistent with the stabilization of a heme water ligand. The CN derivatives of the three proteins are studied to make comparisons under conditions of uniform heme coordination and spin-state. MbCN is dominated by a doming mode near 40 cm(-1), while HRPCN displays a strong oscillation at higher frequency (96 cm(-1)) that can be correlated with the saddling distortion observed, in the X-ray structure. In contrast, CgbCN displays low-frequency coherence spectra that contain strong modes near 30 and 80 cm(-1), probably associated with a combination of heme doming and ruffling. HRPNO displays a strong doming mode near 40 cm(-1) that is activated by photolysis. The damping of the coherent motions is significantly reduced when the heme is shielded from solvent fluctuations by the protein material and reduced still further when T less than or similar to 50 K, as pure dephasing processes due to the protein-solvent phonon bath are frozen out.