Institute of Physics, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.
Department of Plant Physiology, Warsaw University of Life Sciences - SGGW, Warsaw, Poland.
Photochem Photobiol Sci. 2020 Apr 15;19(4):495-503. doi: 10.1039/d0pp00031k.
The keto-carotenoid deinoxanthin, which occurs in the UV-resistant bacterium Deinococcus radiodurans, has been investigated by ultrafast time-resolved spectroscopy techniques. We have explored the excited-state properties of deinoxanthin in solution and bound to the S-layer Deinoxanthin Binding Complex (SDBC), a protein complex important for UV resistance and thermostability of the organism. Binding of deinoxanthin to SDBC shifts the absorption spectrum to longer wavelengths, but excited-state dynamics remain unaffected. The lifetime of the lowest excited state (S1) of isolated deinoxanthin in methanol is 2.1 ps. When bound to SDBC, the S1 lifetime is 2.4 ps, indicating essentially no alteration of the effective conjugation length upon binding. Moreover, our data show that the conformational disorder in both ground and excited states is the same for deinoxanthin in methanol and bound to SDBC. Our results thus suggest a rather loosely bound carotenoid in SDBC, making it very distinct from other carotenoid-binding proteins such as Orange Carotenoid Protein (OCP) or crustacyanin, both of which significantly restrain the carotenoid at the binding site. Three deinoxanthin analogs were found to bind the SDBC, suggesting a non-selective binding site of deinoxanthin in SDBC.
具有抗紫外线辐射特性的细菌——抗辐射球菌中存在酮类类胡萝卜素脱环氧叶黄素，我们利用超快时间分辨光谱技术对其进行了研究。我们探究了游离态和结合于 S 层脱环氧叶黄素结合复合物（SDBC）中的脱环氧叶黄素的激发态特性，SDBC 是一种对生物的抗紫外线辐射和热稳定性很重要的蛋白复合物。脱环氧叶黄素与 SDBC 的结合会使吸收光谱红移，但激发态动力学不受影响。游离态脱环氧叶黄素在甲醇中的最低激发态（S1）的寿命为 2.1 ps。当与 SDBC 结合时，S1 的寿命为 2.4 ps，表明结合后有效共轭长度几乎没有变化。此外，我们的数据表明，在甲醇中游离态和结合态的脱环氧叶黄素的基态和激发态的构象无序度是相同的。因此，我们的研究结果表明 SDBC 中的类胡萝卜素结合较为松散，这与其他类胡萝卜素结合蛋白（如橙色类胡萝卜素蛋白（OCP）或甲壳质蛋白）形成鲜明对比，后者在结合部位显著限制了类胡萝卜素的运动。我们发现三种脱环氧叶黄素类似物可与 SDBC 结合，这表明脱环氧叶黄素在 SDBC 中有一个非选择性的结合部位。
