Mechanism of cryptochrome-mediated photo transduction

描述（由申请人提供）：我们的实验室最近发现，昆虫隐花色素（Cry）的蓝光光激活导致膜快速去极化，并使中央脑神经元的动作电位放电率比基线暗自发放电增加300% （Sheeba等人，2007；Fogle等人，2011）。在没有所有视蛋白为基础的经典光感受器输入的情况下，电生理光响应是稳健的（Fogle et al., 2011）。在通常光不敏感的嗅觉神经元中，Cry基因靶向表达赋予电生理光反应性，这表明Cry表达可能用于光遗传学应用（Fogle et al., 2011）。分子遗传学和药理学实验的结合表明，Cry的光敏性是通过与dCry结合的黄素腺嘌呤二核苷酸（FAD）发色团的氧化还原状态的光激活变化介导的，该发色团随后与细胞质钾通道亚基中的氧化还原传感器偶联并调节钾通道活性。我们建议通过测试缺乏保守的三色氨酸基序列的突变体来扩展这些发现，确定光激活的Cry如何经历从黄素发色团到Cry蛋白表面的氧化还原状态的分子内转移的精确分子机制，这些突变体在其他Cry蛋白中具有传导氧化还原信号的功能。然后，我们将测试氧化还原转移发生在膜中靶蛋白的假设。基于强有力的初步数据表明，dCry光激活氧化还原状态的膜耦合是通过电压门控钾通道发生的，我们将验证dCry随后与电压门控钾通道的膜氧化还原敏感效应物Hyperkinetic beta亚基（Hk）相互作用的假设。我们的初步数据表明，光激活Cry可以快速调节细胞钾电流并使膜电位去极化。我们已经开始测试这一假设，并发现在Hk零突变体果蝇中lLNv电生理光响应几乎完全消失，这表明Hk是基于dcry的新型光导机制的主要膜靶点。我们将确定dCry快速转位到神经元膜上是否会增加电生理光响应的速度和振幅，正如使用基于化学生物学的诱导策略所测试的那样。这些实验为揭示基于氧化还原传感的新型非视蛋白光导机制提供了独特的机会。我们也第一次有机会研究Cry在体内的实时作用，以及确定KvBeta亚基中高度保守的氧化还原传感器的生物学功能的可能性。由于Cry的发色团FAD是普遍表达的，我们的工作可能为一种新的“基于维生素b的”光遗传技术提供基础，该技术适用于不能合成足够水平的视网膜的细胞。

DESCRIPTION (provided by applicant): Our laboratory recently discovered that blue light photoactivation of insect Cryptochrome (Cry) cause rapid membrane depolarization and up to 300% increased action potential firing rate over baseline dark spontaneous firing in central brain neurons (Sheeba et al., 2007; Fogle et al., 2011). The electrophysiological light response is robust in the absence of all opsin-based classical photoreceptor inputs (Fogle et al., 2011). Genetically targeted expression of Cry in normally light-insensitive olfactory neurons confers electrophysiological light responsiveness, indicating that Cry expression may be used for optogenetic applications (Fogle et al., 2011). A combination of molecular-genetic and pharmacological experiments indicate that Cry's light sensitivity is mediated through light-activated changes in the redox state of the flavin adenine dinucleotide (FAD) chromophore bound to dCry which then couples to a redox sensor in cytoplasmic potassium channel subunits and modulate potassium channel activity. We propose to extend these findings by determining the precise molecular mechanism of how light activated Cry undergoes an intramolecular transfer of redox state from the flavin chromophore to the protein surface of Cry by testing mutants which lack a well conserved tri-tryptophan motif characterized in other Cry proteins as conducting redox signals. We will then test the hypothesis that redox transfer takes place to target proteins in the membrane. Based on strong preliminary data that membrane coupling of Cry's light activated redox state occurs through voltage gated potassium channels, we will test the hypothesis that dCry then interacts with membrane redox-sensitive effector Hyperkinetic beta subunit (Hk) of voltage-gated potassium (Kv) channels. Our preliminary data indicates that light activation of Cry rapidly modulates cellular potassium currents and depolarizes the membrane potential. We have begun testing this hypothesis and find that the lLNv electrophysiological light response in almost completely abolished in Hk null mutant flies, suggesting that Hk is the primary membrane target for the novel dCry-based phototransduction mechanism. We will determine whether rapid translocation of dCry to the neuronal membrane increases the speed and the amplitude of the electrophysiological light response, as tested using a chemical biology-based inducible strategy. These experiments provide a unique opportunity to unravel a novel non-opsin phototransduction mechanism based on redox sensing. We have also the first opportunity to examine real-time actions of Cry in vivo and the possibility of determining a biological function for the highly conserved redox sensor in KvBeta subunits. As Cry's chromophore, FAD, is the ubiquitously expressed, our work may provide the basis of a new "Vitamin B-based" optogenetic technology applicable to cells that do not synthesize adequate levels of retinal.