Nohr Daniel, Franz Sophie, Rodriguez Ryan, Paulus Bernd, Essen Lars-Oliver, Weber Stefan, Schleicher Erik
Institute of Physical Chemistry, University of Freiburg, Freiburg, Germany.
University of Marburg, Marburg, Germany.
Biophys J. 2016 Jul 26;111(2):301-311. doi: 10.1016/j.bpj.2016.06.009.
The cryptochrome/photolyase protein family possesses a conserved triad of tryptophans that may act as a molecular wire to transport electrons from the protein surface to the FAD cofactor for activation and/or signaling-state formation. Members from the animal (and animal-like) cryptochrome subclade use this process in a light-induced fashion in a number of exciting responses, such as the (re-)setting of circadian rhythms or magnetoreception; however, electron-transfer pathways have not been explored in detail yet. Therefore, we present an in-depth time-resolved optical and electron-paramagnetic resonance spectroscopic study of two cryptochromes from Chlamydomonas reinhardtii and Drosophila melanogaster. The results do not only reveal the existence of a fourth, more distant aromatic amino acid that serves as a terminal electron donor in both proteins, but also show that a tyrosine is able to fulfill this very role in Chlamydomonas reinhardtii cryptochrome. Additionally, exchange of the respective fourth aromatic amino acid to redox-inactive phenylalanines still leads to light-induced radical pair formation; however, the lifetimes of these species are drastically reduced from the ms- to the μs-range. The results presented in this study open up a new chapter, to our knowledge, in the diversity of electron-transfer pathways in cryptochromes. Moreover, they could explain unique functions of animal cryptochromes, in particular their potential roles in magnetoreception because magnetic-field effects of light-induced radical pairs strongly depend on distance and orientation parameters.
隐花色素/光解酶蛋白家族拥有一个由色氨酸组成的保守三联体，它可能作为分子导线，将电子从蛋白质表面传输到FAD辅因子，以实现激活和/或信号状态形成。动物（及类似动物）隐花色素亚分支的成员在许多令人兴奋的反应中以光诱导的方式利用这一过程，比如昼夜节律的（重新）设定或磁感受；然而，电子转移途径尚未得到详细研究。因此，我们对莱茵衣藻和黑腹果蝇的两种隐花色素进行了深入的时间分辨光学和电子顺磁共振光谱研究。结果不仅揭示了在这两种蛋白质中存在第四个距离更远的芳香族氨基酸，它作为末端电子供体，还表明在莱茵衣藻隐花色素中酪氨酸能够发挥这一作用。此外，将各自的第四个芳香族氨基酸替换为氧化还原惰性的苯丙氨酸仍会导致光诱导自由基对的形成；然而，这些物种的寿命从毫秒级大幅缩短至微秒级。据我们所知，本研究展示的结果为隐花色素电子转移途径的多样性开启了新的篇章。此外，它们可以解释动物隐花色素的独特功能，特别是它们在磁感受中的潜在作用，因为光诱导自由基对的磁场效应强烈依赖于距离和取向参数。
