Specific damage induced by X-ray radiation and structural changes in the primary photoreaction of bacteriorhodopsin
Specific damage induced by X-ray radiation and structural changes in the primary photoreaction of bacteriorhodopsin
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DOI：
10.1016/s0022-2836(02)01110-5
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发表时间：
2002-11-29
影响因子：
5.6
通讯作者：
Kouyama, T
中科院分区：
文献类型：
--
作者：
Matsui, Y;Sakai, K;Kouyama, T
细菌视紫红质是盐盐菌紫色膜的唯一膜蛋白，具有光驱动质子泵的作用。采用膜融合法制备了细菌视紫红质的三维晶体，研究了其在一次光反应中的结构变化。观察到，当冷冻晶体暴露在低通量的x射线辐射（5 x 10（14）光子mm(-2)）下时，近一半的蛋白质转化为橙色；在450 nm、478 nm和510 nm处出现吸收峰。其余的保持正常的光化学活性，直到活性部位的Asp85被更高通量的x射线辐射（10（16）光子毫米（-2））脱羧。改进了衍射测量的程序，以尽量减少辐射损伤的影响，并确定与初级光反应相关的真实结构变化。我们的K中间体结构模型表明，视网膜多烯链中的希夫碱键和相邻键在很大程度上是扭曲的，因此希夫碱氮原子仍然与位于Asp85附近的水分子相互作用。相对于蛋白质的其他部分，在初级光反应中没有引起明显的位移。(C) 2002 Elsevier Science Ltd.版权所有。
Bacteriorhodopsin, the sole membrane protein of the purple membrane of Halobacterium salinarum, functions as a light-driven proton pump. A 3-D crystal of bacteriorhodopsin, which was prepared by the membrane fusion method, was used to investigate structural changes in the primary photoreaction. It was observed that when a frozen crystal was exposed to a low flux of X-ray radiation (5 x 10(14) photons mm(-2)), nearly half of the protein was converted into an orange species; exhibiting absorption peaks at 450 nm, 478 nn and 510 nm. The remainder retained the normal photochemical activity until Asp85 in the active site was decarboxlyated by a higher flux of X-ray radiation (10(16) photons mm(-2)). The procedure of diffraction measurement was improved so as to minimize the effects of the radiation damage and determine the true structural change associated with the primary photoreaction. Our structural model of the K intermediate indicates that the Schiff base linkage and the adjacent bonds in the polyene chain of retinal are largely twisted so that the Schiff base nitrogen atom still interacts with a water molecule located near Asp85. With respect to the other part of the protein, no appreciable displacement is induced in the primary photoreaction. (C) 2002 Elsevier Science Ltd. All rights reserved.