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Volume-conserving trans-cis isomerization pathways in photoactive yellow protein visualized by picosecond X-ray crystallography

机译:体积节约反式 - 顺式异构化途径在光敏黄色蛋白由皮秒X射线晶体可视化

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摘要

Trans-to-cis isomerization, the key reaction in photoactive proteins, cannot usually occur through the standard one-bond-flip mechanism. Due to spatial constraints imposed by a protein environment, isomerization is likely to proceed via a “volume-conserving” mechanism in which highly-choreographed atomic motions are expected, the details of which have not yet been directly observed. Here we employ time-resolved X-ray crystallography to structurally visualize isomerization of the p-coumaric acid chromophore in photoactive yellow protein with 100 picosecond time resolution and 1.6 Å spatial resolution. The structure of the earliest intermediate (IT) resembles a highly-strained transition state in which the torsion angle is located halfway between the trans and cis isomers. The reaction trajectory of IT bifurcates into two structurally distinct cis intermediates via hula-twist and bicycle-pedal pathways. The bifurcating reaction pathways can be controlled by weakening the hydrogen bond between the chromophore and an adjacent residue via E46Q mutation, which switches off the bicycle-pedal pathway.
机译:反式-顺式异构化是光敏蛋白中的关键反应,通常无法通过标准的单键翻转机制发生。由于蛋白质环境所施加的空间限制,异构化可能会通过“体积守恒”机制进行,在这种机制中可以预期到高度编排的原子运动,但其细节尚未直接观察到。在这里,我们采用时间分辨X射线晶体学在结构上以100皮秒的时间分辨率和1.6Å的空间分辨率可视化了光活性黄色蛋白质中对香豆酸发色团的异构化。最早的中间体(IT)的结构类似于高应变过渡态,其中扭转角位于反式和顺式异构体之间。 IT的反应轨迹通过呼啦扭曲和自行车踏板途径分叉为两个结构不同的顺式中间体。可以通过E46Q突变削弱发色团和相邻残基之间的氢键来控制分叉反应路径,从而关闭自行车踏板路径。

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