Variable Electron Transfer Pathways in an Amphibian Cryptochrome TRYPTOPHAN VERSUS TYROSINE-BASED RADICAL PAIRS
Variable Electron Transfer Pathways in an Amphibian Cryptochrome TRYPTOPHAN VERSUS TYROSINE-BASED RADICAL PAIRS
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DOI：
10.1074/jbc.m112.417725
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发表时间：
2013-03-29
影响因子：
4.8
通讯作者：
Schleicher, Erik
中科院分区：
文献类型：
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作者：
Biskup, Till;Paulus, Bernd;Schleicher, Erik
电子转移反应在许多生物过程中发挥着至关重要的作用。通常，电荷转移会在涉及多个氨基酸残基的长距离内逐步进行。通过时间分辨电子顺磁共振和光谱技术，我们研究了光诱导隐花色素/光解合酶家族蛋白FAD辅因子还原的机制。在这项研究中，我们证明，即使已知是这些蛋白质中有效电子传递途径的三个色氨酸的保守链被阻断，激发的 FAD 从附近氨基酸夺取电子也会触发进一步的电子传递步骤。此外，我们能够表征这种二次电子转移途径，并将所得黄素-氨基酸自由基对的氨基酸伴侣识别为位于蛋白质表面的酪氨酸。这种替代的电子转移途径可以解释为什么中断保守的色氨酸三联体不一定会改变体内隐花色素的光反应。总而言之，我们的结果表明光诱导电子转移是隐花色素的一个强大特性，并且比通常预期的更复杂。
Electron transfer reactions play vital roles in many biological processes. Very often the transfer of charge(s) proceeds stepwise over large distances involving several amino acid residues. By using time-resolved electron paramagnetic resonance and optical spectroscopy, we have studied the mechanism of light-induced reduction of the FAD cofactor of cryptochrome/photolyase family proteins. In this study, we demonstrate that electron abstraction from a nearby amino acid by the excited FAD triggers further electron transfer steps even if the conserved chain of three tryptophans, known to be an effective electron transfer pathway in these proteins, is blocked. Furthermore, we were able to characterize this secondary electron transfer pathway and identify the amino acid partner of the resulting flavin-amino acid radical pair as a tyrosine located at the protein surface. This alternative electron transfer pathway could explain why interrupting the conserved tryptophan triad does not necessarily alter photoreactions of cryptochromes in vivo. Taken together, our results demonstrate that light-induced electron transfer is a robust property of cryptochromes and more intricate than commonly anticipated.