Role of the Propionic Side Chains for the Photoconversion of Bacterial Phytochromes
Role of the Propionic Side Chains for the Photoconversion of Bacterial Phytochromes
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DOI：
10.1021/acs.biochem.9b00526
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发表时间：
2019-08-20
期刊：
影响因子：
2.9
通讯作者：
Hildebrandt, Peter
中科院分区：
文献类型：
--
作者：
Lopez, Maria Fernandez;Nguyen, Anh Duc;Hildebrandt, Peter
含有胆绿素IX α（BV）发色团的细菌光敏色素经历光诱导反应级联以在生理非活性和活性状态之间切换。采用振动光谱和计算的方法，我们分析了BV的丙酸取代基的作用，在母态Pr和Pfr之间的转换在原型（Agp 1）和bathy（Agp 2）光敏色素从农杆菌fabrum。这两种蛋白质与BV单酯（BVM）形成加合物，在丙酸侧链B（PsB）或C（PsC）酯化，但在每种情况下，只有一种单酯加合物是反应性的。在反应性Agp 2-BVM-B复合物（在环B酯化）中，Pfr暗态显示出碱性光敏色素的结构特性，包括质子化的PsC。如在天然Agp 2中，PsC在Pfr光转化的最后步骤中去质子化。然而，伴随的α-螺旋/β-片层的二级结构的变化的舌头被阻止在展开的卷曲环区域的阶段。这一发现以及BVM的互变异构平衡向烯醇形式的转变归因于静电势的剧烈变化。计算进一步表明，PsC的去质子化和His 278的质子化状态控制烯醇互变异构体的反应性，从而占非常缓慢的热回复。虽然强扰动的静电势也被发现为Agp 1-BVM，Pr到PFR的光转化的后果是不太严重。具体地说，舌头的结构转变不会受到损害，甚至会加速热逆转。Agp 1和Agp 2对BV单酯化反应的不同响应表明了不同的光转化机制。
Bacteriophytochromes harboring a biliverdin IX alpha (BV) chromophore undergo photoinduced reaction cascades to switch between physiologically inactive and active states. Employing vibrational spectroscopic and computational methods, we analyzed the role of propionic substituents of BV in the transformations between parent states Pr and Pfr in prototypical (Agp1) and bathy (Agp2) phytochromes from Agrobacterium fabrum. Both proteins form adducts with BV monoesters (BVM), esterified at propionic side chain B (PsB) or C (PsC), but in each case, only one monoester adduct is reactive. In the reactive Agp2-BVM-B complex (esterified at ring B), the Pfr dark state displays the structural properties characteristic of bathy phytochromes, including a protonated PsC. As in native Agp2, PsC is deprotonated in the final step of the Pfr phototransformation. However, the concomitant alpha-helix/beta-sheet secondary structure change of the tongue is blocked at the stage of unfolding of the coiled loop region. This finding and the shift of the tautomeric equilibrium of BVM toward the enol form are attributed to the drastic changes in the electrostatic potential. The calculations further suggest that deprotonation of PsC and the protonation state of His278 control the reactivity of the enol tautomer, thereby accounting for the extraordinarily slow thermal reversion. Although strong perturbations of the electrostatic potential are also found for Agp1-BVM, the consequences for the Pr-to-Pfr phototransformation are less severe. Specifically, the structural transition of the tongue is not impaired and thermal reversion is even accelerated. The different response of Agp1 and Agp2 to monoesterification of BV points to different photoconversion mechanisms.