Flavin reduction activates Drosophila cryptochrome
Flavin reduction activates Drosophila cryptochrome
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DOI：
10.1073/pnas.1313336110
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发表时间：
2013-12-17
影响因子：
11.1
通讯作者：
Crane, Brian R.
中科院分区：
文献类型：
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作者：
Vaidya, Anand T.;Top, Deniz;Crane, Brian R.
在高等生物体中，昼夜节律的诱导依赖于光敏蛋白，该光敏蛋白与由延迟的转录反馈环组成的细胞振荡器进行通信。果蝇隐花色素（dCRY）是果蝇昼夜节律钟的主要感光体，它含有一个C末端尾（CTT）螺旋，该螺旋与FAD辅因子结合，对光信号传导至关重要。光将dCRY FAD还原为阴离子半醌（ASQ）自由基，并增加CTT蛋白水解敏感性，但不会导致CTT化学修饰。蛋白水解敏感性和小角度X射线散射的其他变化定义了蛋白质对光的构象反应，该反应以CTT为中心，但也涉及远离黄素中心的区域。黄素的还原在动力学上与CTT重排偶联。化学还原为ASQ或完全还原的对苯二酚状态产生与光相同的构象响应。振荡蛋白Timeless（TIM）含有一个类似于CTT的序列;相应的肽在光下结合dCRY并保护黄素免受氧化。然而，其中的TIM突变体仍然经历durine介导的降解。因此，光还原为ASQ释放dCRY CTT并促进与TIM的至少一个区域的结合。由光或细胞还原剂引起的黄素还原可能是CRY激活的一般机制。
Entrainment of circadian rhythms in higher organisms relies on light-sensing proteins that communicate to cellular oscillators composed of delayed transcriptional feedback loops. The principal photoreceptor of the fly circadian clock, Drosophila cryptochrome (dCRY), contains a C-terminal tail (CTT) helix that binds beside a FAD cofactor and is essential for light signaling. Light reduces the dCRY FAD to an anionic semiquinone (ASQ) radical and increases CTT proteolytic susceptibility but does not lead to CTT chemical modification. Additional changes in proteolytic sensitivity and small-angle X-ray scattering define a conformational response of the protein to light that centers at the CTT but also involves regions remote from the flavin center. Reduction of the flavin is kinetically coupled to CTT rearrangement. Chemical reduction to either the ASQ or the fully reduced hydroquinone state produces the same conformational response as does light. The oscillator protein Timeless (TIM) contains a sequence similar to the CTT; the corresponding peptide binds dCRY in light and protects the flavin from oxidation. However, TIM mutants therein still undergo dCRY-mediated degradation. Thus, photoreduction to the ASQ releases the dCRY CTT and promotes binding to at least one region of TIM. Flavin reduction by either light or cellular reductants may be a general mechanism of CRY activation.