Hydrogen Bonding Environments in the Photocycle Process around the Flavin Chromophore of the AppA-BLUF domain
Hydrogen Bonding Environments in the Photocycle Process around the Flavin Chromophore of the AppA-BLUF domain
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DOI：
10.1021/jacs.8b05123
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发表时间：
2018-09-26
影响因子：
15
通讯作者：
Kandori, Hideki
中科院分区：
文献类型：
--
作者：
Iwata, Tatsuya;Nagai, Takashi;Kandori, Hideki
已知在作为光传感器蛋白质的发色团的黄素中有三种光化学反应，反映了黄素在黄素酶中的各种催化反应。使用黄素FAD（BLUF）结构域的蓝光传感器与其他黄素结合光感受器相比表现出独特的光反应，因为发色团在未光解和中间状态之间不改变其化学结构。相反，氢键环境被改变，由此FAD附近的保守Gln和Tyr残基起着至关重要的作用。对这种行为的一种建议是保守的谷氨酰胺将其化学结构从酮基改变为烯醇。我们应用光诱导差分傅里叶变换红外（FTIR）光谱AppA-BLUF。AppA-BLUF的光谱在N-15-Gln标记后表现出与先前报道的来自B1 rB（不同的BLUF结构域）的光谱不同的特征。根据量子力学/分子力学（QM/MM）计算，将FTIR信号解释为AppA-BLUF结构域中Gln 63侧链的酮-烯醇互变异构和旋转。前者与B1 rB的结果一致，但后者不是由先前的研究唯一确定的。QM/MM计算还表明，红外信号的形状取决于Trp侧链是否与Gln侧链形成氢键而受到影响。FTIR光谱和QM/MM模拟得出结论，Trp 104没有翻转，而是保持在中间状态。相比之下，我们的数据显示，在相应的位置在BlrB的色氨酸残基面向外，在这两个国家。
Three kinds of photochemical reactions are known in flavins as chromophores of photosensor proteins, reflecting the various catalytic reactions of the flavin in flavoenzymes. Sensor of blue light using the flavin FAD (BLUF) domains exhibit a unique photoreaction compared with other flavin-binding photoreceptors in that the chromophore does not change its chemical structure between unphotolyzed and intermediate states. Rather, the hydrogen bonding environment is altered, whereby the conserved Gln and Tyr residues near FAD play a crucial role. One proposal for this behavior is that the conserved Gln changes its chemical structure from a keto to an enol. We applied light-induced difference Fourier transform infrared (FTIR) spectroscopy to AppA-BLUF. The spectra of AppA-BLUF exhibited a different feature upon N-15-Gln labeling compared with the previously reported spectra from B1rB, a different BLUF domain. The FTIR signals were interpreted from quantum mechanics/molecular mechanics (QM/MM) calculation as the keto-enol tautomerization and rotation of the Gln63 side chain in the AppA-BLUF domain. The former was consistent with the result from B1rB, but the latter was not uniquely determined by the previous study. QM/MM calculation also indicated that the infrared signal shape is influenced depending on whether a Trp side chain forms a hydrogen bond with the Gln side chain. FTIR spectra and QM/MM simulations concluded that Trp104 does not flip out but is maintained in the intermediate state. In contrast, our data revealed that the Trp residue at the corresponding position in BlrB faces outward in both states.