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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Three strategically placed hydrogen-bonding residues convert a proton pump into a sensory receptor
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Three strategically placed hydrogen-bonding residues convert a proton pump into a sensory receptor

机译：三个策略性放置的氢键残基将质子泵转换为感觉受体

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摘要

In haloarchaea, light-driven ion transporters have been modified by evolution to produce sensory receptors that relay light signals to transducer proteins controlling motility behavior. The proton pump bacteriorhodopsin and the phototaxis receptor sensory rhodopsin 11 (SRII) differ by 74% of their residues, with nearly all conserved residues within the photoreactive retinal-binding pocket in the membrane-embedded center of the proteins. Here, we show that three residues in bacteriorhodopsin replaced by the corresponding residues in SRII enable bacteriorhodopsin to efficiently relay the retinal photoisomerization signal to the SRII integral membrane transducer (HtrII) and induce robust phototaxis responses. A single replacement (Ala-215-Thr), bridging the retinal and the membrane-embedded surface, confers weak phototaxis signaling activity, and the additional two (surface substitutions Pro-200-Thr and Val-210-Tyr), expected to align bacteriorhodopsin and HtrII in similar juxtaposition as SRII and HtrII, greatly enhance the signaling. In SRII, the three residues form a chain of hydrogen bonds from the retinal's photoisomerized C-13=C-14 double bond to residues in the membrane-embedded alpha-helices of HtrII. The results suggest a chemical mechanism for signaling that entails initial storage of energy of photoisomerization in SRII's hydrogen bond between Tyr-174, which is in contact with the retinal, and Thr-204, which borders residues on the SRII surface in contact with HtrII, followed by transfer of this chemical energy to drive structural transitions in the transducer helices. The results demonstrate that evolution accomplished an elegant but simple conversion: The essential differences between transport and signaling proteins in the rhodopsin family are far less than previously imagined.
机译：在卤古菌中，光驱动的离子转运蛋白已通过进化得到修饰，以产生将光信号传递至控制运动行为的换能蛋白的感觉受体。质子泵细菌视紫红质和趋光性受体感觉视紫红质11（SRII）的残基相差74％，几乎所有保守的残基都位于蛋白质膜嵌入中心的光反应性视网膜结合袋中。在这里，我们显示细菌视紫红质中的三个残基被SRII中的相应残基取代，使细菌视紫红质能够有效地将视网膜光异构化信号传递给SRII整体膜换能器（HtrII），并诱导强大的趋光性。桥接视网膜和膜嵌入表面的单个替代物（Ala-215-Thr）赋予弱的趋光性信号传导活性，另外两个替代物（表面替代物Pro-200-Thr和Val-210-Tyr）有望对齐细菌视紫红质和HtrII的并置与SRII和HtrII相似，大大增强了信号传导。在SRII中，这三个残基从视网膜的光异构化C-13 = C-14双键到HtrII的膜嵌入α螺旋中的残基形成氢键链。结果表明，信号传导的化学机制需要在与视网膜接触的Tyr-174与与HtrII接触的SRII表面上的残基接壤的Thr-204之间，SRII的氢键中光异构化能量的初始存储，然后转移此化学能以驱动换能器螺旋结构的结构转变。结果表明，进化实现了优雅而简单的转换：视紫红质家族中转运蛋白和信号蛋白之间的本质差异远小于以前的想象。

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