Water molecule rearrangements around Leu93 and Trp182 in the formation of the L intermediate in bacteriorhodopsin's photocycle.
Water molecule rearrangements around Leu93 and Trp182 in the formation of the L intermediate in bacteriorhodopsin's photocycle.
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细菌视紫红质光循环中 L 中间体形成过程中 Leu93 和 Trp182 周围的水分子重排。
DOI：
10.1021/bi020532n
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
Ebrey,ThomasG
中科院分区：
文献类型：
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作者：
Maeda,Akio;Tomson,FarolL;Gennis,RobertB;Balashov,SergeiP;Ebrey,ThomasG
在细菌视紫红质的初始光化学事件中发色团异构化后，主要光产物 K 热转变为 L 中间体，为后续步骤 (L → M) 中的希夫碱去质子化准备颜料。 L 形成时，内部水分子的氢键发生显着变化。其中一些流动水可能参与改变希夫碱的 pK 值以及质子受体 Asp85 的 pK 值以允许质子运动 [Maeda, A. (2001)Biochemistry (Moscow) 66, 1555−1569]。在这里，我们表明，Leu93 和 Trp182（靠近发色团 13-甲基基团的残基）的突变允许在比野生型低得多的温度（80 K 而不是 140 K）下形成 L。此外，由于 L 所特有的弱结合水而产生的强带已经存在于每个突变体的初始（未光解）状态中，位于 2632 cm-1（以 D2O 计），但野生型中不存在。与 2589 cm-1 处的 L 谱带相比，这一独特的、强烈的水谱带发生了偏移，但与 L' 中看到的谱带一致，L' 是野生型 L 在 80 K 时形成的全反式光产物。我们提出，L93M 和 W182F 突变会诱导这些色素的未光解状态下一个或多个水分子的氢键变化，这与野生型 L 形成时发生的氢键变化类似，从而促进即使在 80 K 时也能形成 L。我们推断 L 的形成涉及包括视网膜、Trp182 和 Leu93 在内的位点的扰动，并且该结构通过与水分子的氢键重排而暂时稳定。
After the chromophore's isomerization in the initial photochemical event in bacteriorhodopsin, the primary photoproduct K makes a thermal transition to the L intermediate, which prepares the pigment for Schiff base deprotonation in the following step (L → M). Substantial changes in the hydrogen bonding of internal water molecules take place upon L formation. Some of these mobile waters are probably involved in changing the pKof the Schiff base and perhaps that of the proton acceptor Asp85 to allow proton movement [Maeda, A. (2001)Biochemistry (Moscow) 66, 1555−1569]. Here we show that mutations of Leu93 and Trp182, residues close to the 13-methyl group of the chromophore, allow the formation of L at much lower temperatures than in the wild type (80 K instead of 140 K). Moreover, an intense band due to weakly bound water that is peculiar for L was already present in the initial (unphotolyzed) state of each mutant at 2632 cm-1(in D2O) but not in the wild type. This unique, intense water band is shifted compared to the L band at 2589 cm-1but coincides with the band seen in L‘, the all-trans photoproduct of wild-type L formed at 80 K. We propose that the L93M and W182F mutations induce changes in the hydrogen bonding of one or more water molecules in the unphotolyzed states of these pigments, which are similar to those H-bonding changes that take place upon formation of L in the wild type, and thus facilitate the formation of L even at 80 K. We infer that L formation involves perturbation of a site which includes retinal, Trp182, and Leu93, and this structure is temporarily stabilized by rearranged hydrogen bonds with water molecules.