RESONANCE RAMAN-SPECTROSCOPY OF IRON(III) TETRATHIOLATE COMPLEXES - IMPLICATIONS FOR THE CONFORMATION AND FORCE-FIELD OF RUBREDOXIN
RESONANCE RAMAN-SPECTROSCOPY OF IRON(III) TETRATHIOLATE COMPLEXES - IMPLICATIONS FOR THE CONFORMATION AND FORCE-FIELD OF RUBREDOXIN
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DOI：
10.1021/ja00095a017
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发表时间：
1994-08-10
影响因子：
15
通讯作者：
SPIRO, TG
中科院分区：
文献类型：
--
作者：
CZERNUSZEWICZ, RS;KILPATRICK, LK;SPIRO, TG
分析了一系列四硫醇铁配合物的振动光谱，包括[Fe（SMe）（4）]（-），[Fe（SEt）（4）]（-）和[Fe（SEt）（4（S-2-o-xyl）（2）]（-）（SMe =甲基硫醇盐，SEt =乙基硫醇盐，S-2-o-xyl =邻二甲苯-α，α '-二硫醇盐），使用同位素异构体的共振拉曼（RR）和红外光谱（Fe-54、S-34和H-2）。借助法向坐标分析计算，使用所有三种物质的一致力场进行计算。这些结果允许重新分析和建模先前发表的RR光谱氧化rubredoxin中，Fe 3+是由四个半胱氨酸侧链绑定。配合物的光谱表明：（1）由于S-C键在S-Fe-S面外取向，三重简并nu（3）Fe-S伸缩模分裂，对称性从Td降低，（2）由于S-Fe-S角的不相等，在[Fe（SMe）（4）]（-）中进一步分裂;（3）通过与[Fe（SEt）（4）]（-）中的甲基扭转模式的相互作用而提高v1 Fe-S呼吸频率;和（4）由于[Fe（S-2-o-xyl）（2）]（-）中的螯合环约束而混合Fe-S伸缩和S-C-C弯曲模式。红氧还蛋白RR带和Fe-54同位素位移用相同的力场建模，揭示了由于两个半胱氨酸配体的180度FeS-CC二面角导致的Fe-S/S-C-C混合的主导影响。rubredoxin的yl频率的正确计算需要显着减少的Fe-S拉伸力常数，相对于类似物的复合物。这种减少被提出来反映H-键合到蛋白质中的半胱氨酸S原子的影响。
Vibrational spectra are analyzed for a series of iron(III) tetrathiolate complexes, including [Fe(SMe)(4)](-), [Fe(SEt)(4)](-), and [Fe(S-2-o-xyl)(2)](-) (SMe = methylthiolate, SEt = ethylthiolate, and S-2-o-xyl = o-xylene-alpha,alpha'-dithiolate), using resonance Raman (RR) and infrared spectra of isotopomers (Fe-54, S-34, and H-2). Assignments are made with the aid of normal coordinate analysis calculations, using a consistent force field for all three species. These results permit reanalysis and modeling of previously published RR spectra of oxidized rubredoxin in which Fe3+ is bound by four cysteinate side chains. The spectra of the analog complexes reveal (1) symmetry lowering from Td, manifested in the splitting of the triply degenerate nu(3) Fe-S stretching mode, due to the S-C bonds being oriented out of the S-Fe-S planes; (2) further splitting, in the case of [Fe(SMe)(4)](-), due to inequivalence of the S-Fe-S angles; (3) elevation of the vl Fe-S breathing frequency via interaction with methyl torsional modes in [Fe(SEt)(4)](-); and (4) mixing of Fe-S stretching and S-C-C bending modes due to the chelate ring constraints in [Fe(S-2-o-xyl)(2)](-). The rubredoxin RR bands and Fe-54 isotope shifts are modeled with the same force field, revealing a dominant influence of Fe-S/S-C-C mixing due to 180 degrees FeS-CC dihedral angles for two of the cysteinate ligands. Proper calculation of the yl frequency of rubredoxin requires a significant reduction of the Fe-S stretching force constant, relative to that of the analog complexes. This reduction is proposed to reflect the influence of H-bonding to the cysteinate S atoms in the protein.