Properties and photochemistry of a halorhodopsin from the haloalkalophile, Natronobacterium pharaonis.
Properties and photochemistry of a halorhodopsin from the haloalkalophile, Natronobacterium pharaonis.
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DOI：
10.1016/s0021-9258(19)40007-0
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发表时间：
1990-01
期刊：
影响因子：
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通讯作者：
Albert Duschl;J. Lanyi;László Zimányi
中科院分区：
文献类型：
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作者：
Albert Duschl;J. Lanyi;László Zimányi
Pharaonis卤视紫质是一种光驱动的氯离子运输系统，类似于前面描述的卤视紫质，但我们发现它运输硝酸盐的效率与氯离子一样高。我们用门控多道分析仪研究了纯化的洗涤剂增溶的法老花色素的光反应。在生理盐浓度下(4M氯化钠)，光循环中间产物的吸收光谱和速率常数与卤视紫红质相似。在含有硝酸盐的缓冲液中，卤视紫红质表现出第二个截短的光周期；当阴离子以阻止运输的方式结合时，色素的光反应中的这种差异就会发生。由于在运输过程中缺乏阴离子专一性，卤紫红质的光循环几乎不受硝酸盐取代氯离子的影响。所有可能在阴离子结合中起作用的埋藏的正电荷残基在两种色素中都是保守的。然而，在推测的螺旋C的胞外端，在卤视紫红质中发现了精氨酸残基，但在法老鱼卤视紫质中没有，并且卤视紫质中假定螺旋A和B之间的富含精氨酸的片段被法老鱼卤视紫质中不带正电的序列所取代(Lanyi，J.K.，Duschl，A.，Hatfield，G.W.，May，K.和Oester helt，D.(1990)J.Biol)。化学。265、1253-1260)。这两种变化中的一种或两种可能解释了这两种蛋白质在阴离子选择性上的差异。
Pharaonis halorhodopsin is a light-driven transport system for chloride, similarly to the previously described halorhodopsin, but we find that it transports nitrate as effectively as chloride. We studied the photoreactions of the purified, detergent-solubilized pharaonis pigment with a gated multichannel analyzer. At a physiological salt concentration (4 M NaCl), the absorption spectra and rate constants of rise and decay for intermediates of the photocycle were similar to those for halorhodopsin. In buffer containing nitrate, halorhodopsin exhibits a second, truncated photocycle; this difference in the photoreaction of the pigment occurs when an anion is bound in such a way as to preclude transport. As expected from the lack of anion specificity in the transport, the photocycle of pharaonis halorhodopsin was nearly unaffected by replacement of chloride with nitrate. All presumed buried positively charged residues, which might play a role in anion binding, are conserved in the two pigments. At the extracellular end of the presumed helix C, however, an arginine residue is found in halorhodopsin, but not in pharaonis halorhodopsin, and an arginine-rich segment between the presumed helices A and B in halorhodopsin is replaced by a less positively charged sequence in pharaonis halorhodopsin (Lanyi, J. K., Duschl, A., Hatfield, G. W., May, K., and Oesterhelt, D. (1990) J. Biol. Chem. 265, 1253-1260). One or both of these alterations may explain the difference in the anion selectivity of the two proteins.