Chloride cofactor in the photosynthetic oxygen-evolving complex studied by Fourier transform infrared spectroscopy
Chloride cofactor in the photosynthetic oxygen-evolving complex studied by Fourier transform infrared spectroscopy
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DOI：
10.1021/bi026595n
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发表时间：
2002-11-19
期刊：
影响因子：
2.9
通讯作者：
Ono, TA
中科院分区：
文献类型：
--
作者：
Hasegawa, K;Kimura, Y;Ono, TA
利用傅里叶变换红外（FTIR）光谱，利用中频S-2/S-1差谱，研究了光合放氧复合体（OEC）中氯辅因子的变化，以确定Cl-耗竭和单价阴离子取代的影响。Cl-耗尽导致酰胺I和II振动模式的大部分消失，并诱导特征修改的Mn簇的羧酸根配体的伸缩模式的功能。正常的光谱特征，很大程度上恢复了Cl-的补充，除了酰胺带的一些变化。Br-，I-，或NO3-取代的光谱的总体特征是类似的Cl-重建的光谱，与他们的能力，以支持析氧一致。与此相反，光谱显着改变的取代Cl-与F-或CH 3COO-，这导致显着的抑制和扭曲的羧酸和酰胺带。NO_3 ~-恢复的放氧活性与此相当。由Cl-在有限的光照条件下测量时，表明NO3-取代的OEC是完全活跃的氧释放，虽然与缓慢的周转率。（NO3-）-N-14-取代和（NO3-）-N-15-取代的S-2/S-1差谱之间的双差谱在1400-1300 cm（-1）区域显示了由于NO3-与Cl-位结合而产生的不对称NO伸缩模式的同位素谱带。这证明了Cl-位点和Mn簇之间的结构耦合。一个建议的模型的同位素带表明，Cl-以及NO3-是不直接与锰簇，并存在于一个更对称的配置和较弱的结合状态中的S-2状态比在S-1状态。这些结果还表明，Cl-是所需的Mn簇的特定的羧酸配体的结构的变化，以及从S-1到S-2的过渡后的蛋白质基质的肽骨架。
Fourier transform infrared (FTIR) spectroscopy, using midfrequency S-2/S-1 FTIR difference spectra, has been applied to studies of chloride cofactor in the photosynthetic oxygen-evolving complex (OEC) to determine the effects of Cl- depletion and monovalent anion substitution. Cl- depletion resulted in the disappearance of a large part of the amide I and II vibrational modes, and induced characteristic modification in the features of the stretching modes of the carboxylate ligands of the Mn cluster. The normal spectral features were largely restored by replenishment of Cl- except for some changes in amide bands. The overall features of Br--, I--, or NO3--substituted spectra were similar to those of the Cl-reconstituted spectrum, consistent with their ability to support oxygen evolution. In contrast, the spectrum was significantly altered by the replacement of Cl- with F- or CH3COO-, which resulted in marked suppression and distortion of both the carboxylate and amide bands. The activity of oxygen evolution restored by NO3- was as high as that. by Cl- when measured under limited light conditions, indicating that the NO3--substituted OEC is fully active in oxygen evolution, although with a slow turnover rate. The double-difference spectrum between the (NO3-)-N-14-substituted and (NO3-)-N-15-substituted S-2/S-1 difference spectrum showed isotopic bands for asymmetric NO stretching mode in the region of 1400-1300 cm(-1) due to NO3- bound to the Cl- site. This demonstrated structural coupling between the Cl- site and the Mn cluster. A proposed model for the isotopic bands suggested that Cl- as well as NO3- is not directly associated with the Mn cluster and exists in a more symmetric configuration and weaker binding state in the S-2 state than in the S-1 state. These results also suggest that Cl- is required for changes in the structure of the specific carboxylate ligand of the Mn cluster as well as the peptide backbone of protein matrixes upon the transition from S-1 to S-2.