Ochmann Miguel, Harich Jessica, Ma Rory, Freibert Antonia, Kim Yujin, Gopannagari Madhusudana, Hong Da Hye, Nam Daewoong, Kim Sangsoo, Kim Minseok, Eom Intae, Lee Jae Hyuk, Yorke Briony A, Kim Tae Kyu, Huse Nils
Department of Physics, University of Hamburg and Center for Free-Electron Laser Science, Hamburg, Germany.
Pohang Accelerator Laboratory, POSTECH, Pohang, Republic of Korea.
Nat Commun. 2024 Oct 13;15(1):8838. doi: 10.1038/s41467-024-52748-x.
The photolysis of disulfide bonds is implicated in denaturation of proteins exposed to ultraviolet light. Despite this biological relevance in stabilizing the structure of many proteins, the mechanisms of disulfide photolysis are still contested after decades of research. Herein, we report new insight into the photochemistry of L-cystine in aqueous solution by femtosecond X-ray absorption spectroscopy at the sulfur K-edge. We observe homolytic bond cleavage upon ultraviolet irradiation and the formation of thiyl radicals as the single primary photoproduct. Ultrafast thiyl decay due to geminate recombination proceeds at a quantum yield of >80 % within 20 ps. These dynamics coincide with the emergence of a secondary product, attributed to the generation of perthiyl radicals. From these findings, we suggest a mechanism of perthiyl radical generation from a vibrationally excited parent molecule that asymmetrically fragments along a carbon-sulfur bond. Our results point toward a dynamic photostability of the disulfide bridge in condensed-phase.
二硫键的光解与暴露于紫外线下的蛋白质变性有关。尽管这在稳定许多蛋白质的结构方面具有生物学相关性，但经过数十年的研究，二硫键光解的机制仍存在争议。在此，我们通过硫 K 边的飞秒 X 射线吸收光谱法报告了对水溶液中 L-胱氨酸光化学的新见解。我们观察到紫外线照射下的均裂键断裂以及作为单一初级光产物的硫自由基的形成。由于双生复合导致的超快硫自由基衰减在 20 皮秒内以大于 80% 的量子产率进行。这些动力学与归因于过硫自由基产生的次级产物的出现相吻合。基于这些发现，我们提出了一种从振动激发的母体分子生成过硫自由基的机制，该母体分子沿着碳-硫键不对称断裂。我们的结果表明凝聚相中双硫键具有动态光稳定性。
