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首页> 外文期刊>Biochemistry >Heterogeneity Effects in the Binding of All-Trans Retinal to Bacterio-opsin.
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Heterogeneity Effects in the Binding of All-Trans Retinal to Bacterio-opsin.

机译：异质性效应在全逆视网膜与细菌Opsin的结合中。

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The special trimeric structure of bacteriorhodopsin (bR) in the purple membrane of Halobacterium salinarum, and especially, the still controversial question as to whether the three protein components are structurally and functionally identical, have been subject to considerable work. In the present work, the problem is approached by studying the reconstitution reaction of the bR apo-protein with all-trans retinal, paying special attention to the effects of the apo-protein/retinal (P:R) ratio. The basic observation is that at high P:R values, the reconstitution reaction proceeds via two distinct, fast and slow, pathways associated with two different pre-pigment precursors absorbing at 430 nm (P(430)) and 400 nm (P(400)), respectively. These two reactions, exhibiting 2:1 (P(430)/P(400)) amplitude ratios, are markedly affected by the P:R value. The principal feature is the acceleration of the P(400) --> bR transition at low P:R ratios. The data are interpreted in terms of a scheme in which the added retinal first occupies two protein retinal traps, R(1) and R(2), from which it is transferred to two spectroscopically distinct binding sites corresponding to the two pre-pigments, P(430) and P(400), respectively. Two noncovalently bound retinal molecules occupy two P(430) sites of the bR trimer, while one (P(400)) occupies the third. Binding is completed by generating the retinal-protein covalent bond. Analogous experiments were also carried out with an aromatic bR chromophore and with the D85N bR mutant. The accumulated data clearly point out the heterogeneity of the binding reaction intermediates, in which two are clearly distinct from the third. However, CD spectroscopy strongly suggests that even the two P(430) sites are not structurally identical. The heterogeneity of the P intermediates in the binding reaction can be accounted for, either by being induced by cooperativity or by an intrinsic heterogeneity that is already present in the apoprotein. The question as to whether the final reconstituted pigment, as well as native bR, are nonhomogeneous should be the subject of future studies.
机译：卤素氧化渣紫膜（Br）的特殊三聚体结构，尤其是三种蛋白质组分在结构上和功能相同的仍然存在争议的问题，已经受到相当大的作用。在本作工作中，通过研究BR APO-蛋白与全转蛋白的重构反应来接近问题，特别注意APO-蛋白/视网膜（P：R）比率的影响。基本观察是，在高p：r值下，重构反应通过两个不同的，快速，缓慢，与在430 nm（p（430））和400nm（p（400）的含量吸收））， 分别。表现出2：1（P（430）/ p（400））幅度比的这两种反应显着受到P：R值的影响。主要特征是在低P：R比下的P（400） - > BR转变的加速度。根据其中添加的视网膜首先占用两种蛋白质视网膜疏水阀，R（1）和R（2）的方案来解释数据，从中转移到对应于两个预选的两个光谱上不同的结合位点， P（430）和P（400）分别。两个非共价结合的视网膜分子占据BR三聚体的两个P（430）位点，而其中（P（400））占据第三个。通过产生视网膜蛋白共价键完成结合。也用芳族Br发色团和D85N Br突变体进行类似的实验。累积的数据清楚地指出了结合反应中间体的异质性，其中两个显然不同于第三种。然而，CD光谱强烈表明，即使两个P（430）位点也没有结构上相同。通过合作诱导或通过已经存在于甲壳素中的内在异质性，可以考虑结合反应中的P中间体的异质性。关于最终重构颜料以及天然Br，非均匀的问题应该是未来研究的主题。

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