Cryptochrome blue light photoreceptors are activated through interconversion of flavin redox states
Cryptochrome blue light photoreceptors are activated through interconversion of flavin redox states
复制标题
DOI：
10.1074/jbc.m609842200
复制
发表时间：
2007-03-30
影响因子：
4.8
通讯作者：
Ahmad, Margaret
中科院分区：
文献类型：
--
作者：
Bouly, Jean-Pierre;Schleicher, Erik;Ahmad, Margaret
隐花色素是在植物、动物和人类中发现的蓝光感应光感受器。已知它们在生物钟的调节和发育中发挥关键作用。然而，尽管与光解酶DNA修复酶有惊人的结构相似性，但隐花色素不能修复双链DNA，其作用机制尚不清楚。最近，一个蓝光依赖的分子内电子转移到激发态黄素的特点，并提出作为光活化的主要机制。由此形成的稳定的中性黄素半醌中间体使得光感受器在体外除了吸收蓝光之外还吸收绿色/黄色光（500 - 630 nm）。在这里，我们表明，拟南芥隐花色素激活蓝光可以抑制绿色光在体内的辅因子氧化还原状态的变化一致。我们进一步表征了活细胞中隐花色素（cry 1）蛋白的光依赖性变化，这与体外纯化的cry 1的光还原相匹配。这些实验是使用荧光吸收/发射和EPR在全细胞上进行的，从而代表了在体内监测已知光感受器的活性状态的少数实例之一。这些结果表明，通过蓝光的cryl活化引发了黄酰半醌信号传导状态的形成，该状态可以被绿色光转化为无活性形式。总之，通过黄素光还原激活隐花色素是蓝光光感受器的一种新的可逆机制。这种光循环可能具有适应性意义，用于感知多种生物的光环境质量。
Cryptochromes are blue light-sensing photoreceptors found in Plants, animals, and humans. They are known to play key roles in the regulation of the circadian clock and in development. However, despite striking structural similarities to photolyase DNA repair enzymes, cryptochromes do not repair double-stranded DNA, and their mechanism of action is unknown. Recently, a blue light-dependent intramolecular electron transfer to the excited state flavin was characterized and proposed as the primary mechanism of light activation. The resulting formation of a stable neutral flavin semiquinone intermediate enables the photoreceptor to absorb green/yellow light (500 - 630 nm) in addition to blue light in vitro. Here, we demonstrate that Arabidopsis cryptochrome activation by blue light can be inhibited by green light in vivo consistent with a change of the cofactor redox state. We further characterize light-dependent changes in the cryptochromel (cry1) protein in living cells, which match photoreduction of the purified cryl in vitro. These experiments were performed using fluorescence absorption/emission and EPR on whole cells and thereby represent one of the few examples of the active state of a known photoreceptor being monitored in vivo. These results indicate that cryl activation via blue light initiates formation of a flavosemiquinone signaling state that can be converted by green light to an inactive form. In summary, cryptochrome activation via flavin photoreduction is a reversible mechanism novel to blue light photoreceptors. This photocycle may have adaptive significance for sensing the quality of the light environment in multiple organisms.