Iron-sulfur clusters are inorganic cofactors found in many proteins involved in fundamental biological processes. The prokaryotic DNA repair photolyase PhrB carries a four-iron-four-sulfur cluster ([4Fe4S]) in addition to the catalytic flavin adenine dinucleotide (FAD) and a second cofactor ribolumazine. Our recent study suggested that the [4Fe4S] cluster functions as an electron cache to coordinate two interdependent photoreactions of the FAD and ribolumazine. Here, we report the crystallography observations of light-induced responses in PhrB using the cryo-trapping method and in situ serial Laue diffraction at room temperature. We capture strong signals that depict electron density changes arising from quantized electronic movements in the [4Fe4S] cluster. Our data reveal the mixed valence layers of the [4Fe4S] cluster due to spin coupling and their dynamic responses to light-induced redox changes. The quantum effects imaged by the decomposition of electron density changes have shed light on the emerging roles of metal clusters in proteins.

铁硫簇是在参与基本生物过程的许多蛋白质中发现的无机辅助因子。原核 DNA 修复光裂合酶 PhrB 除了催化黄素腺嘌呤二核苷酸 (FAD) 和第二个辅因子核博鲁嗪外，还携带四铁四硫簇 ([4Fe4S])。我们最近的研究表明，[4Fe4S]簇作为电子缓存来协调 FAD 和核博鲁马嗪的两个相互依赖的光反应。在这里，我们报告了使用冷冻捕获方法和室温下原位连续劳厄衍射对 PhrB 中光诱导反应的晶体学观察。我们捕获了强烈的信号，这些信号描述了 [4Fe4S] 簇中量子化电子运动引起的电子密度变化。我们的数据揭示了由于自旋耦合而产生的 [4Fe4S] 簇的混合价层及其对光诱导氧化还原变化的动态响应。通过电子密度变化分解成像的量子效应揭示了金属簇在蛋白质中的新兴作用。