Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Taiwan.
RIKEN SPring-8 Center, Sayo, Hyogo, Japan.
Nat Chem. 2022 Jun;14(6):677-685. doi: 10.1038/s41557-022-00922-3. Epub 2022 Apr 7.
Flavin coenzymes are universally found in biological redox reactions. DNA photolyases, with their flavin chromophore (FAD), utilize blue light for DNA repair and photoreduction. The latter process involves two single-electron transfers to FAD with an intermittent protonation step to prime the enzyme active for DNA repair. Here we use time-resolved serial femtosecond X-ray crystallography to describe how light-driven electron transfers trigger subsequent nanosecond-to-microsecond entanglement between FAD and its Asn/Arg-Asp redox sensor triad. We found that this key feature within the photolyase-cryptochrome family regulates FAD re-hybridization and protonation. After first electron transfer, the FAD isoalloxazine ring twists strongly when the arginine closes in to stabilize the negative charge. Subsequent breakage of the arginine-aspartate salt bridge allows proton transfer from arginine to FAD. Our molecular videos demonstrate how the protein environment of redox cofactors organizes multiple electron/proton transfer events in an ordered fashion, which could be applicable to other redox systems such as photosynthesis.
黄素辅酶普遍存在于生物氧化还原反应中。DNA 光解酶的黄素辅基（FAD）利用蓝光进行 DNA 修复和光还原。后一过程涉及到两个向 FAD 的单电子转移，以及间歇性的质子化步骤，以启动酶的 DNA 修复活性。在这里，我们使用时间分辨的连续飞秒 X 射线晶体学来描述光驱动的电子转移如何引发 FAD 与其 Asn/Arg-Asp 氧化还原传感器三联体之间随后的纳秒到微秒的纠缠。我们发现，在光解酶-隐花色素家族中，这一关键特征调节 FAD 的再杂交和质子化。第一次电子转移后，当精氨酸靠近时，FAD 的异咯嗪环强烈扭曲，以稳定负电荷。随后精氨酸-天冬氨酸盐桥的断裂允许质子从精氨酸转移到 FAD。我们的分子视频演示了氧化还原辅因子的蛋白质环境如何以有序的方式组织多个电子/质子转移事件，这可能适用于其他氧化还原系统，如光合作用。
