Abstract：
Orexinergic neurons are critically involved in regulating arousal, wakefulness, and appetite. Their dysfunction has been associated with sleeping disorders, and non-peptide drugs are currently being developed to treat insomnia and narcolepsy. Yet, no light-regulated agents are available to reversibly control their activity. To meet this need, a photoswitchable peptide analogue of the endogenous neuroexcitatory peptide orexin-B was designed, synthesized, and tested in vitro and in vivo. This compound - photorexin - is the first photo-reversible ligand reported for orexin receptors. It allows dynamic control of activity in vitro (including almost the same efficacy as orexin-B, high nanomolar potency, and subtype selectivity to human OX2 receptors) and in vivo in zebrafish larvae by direct application in water. Photorexin induces dose- and light-dependent changes in locomotion and a reduction in the successive induction reflex that is associated with sleep behavior. Molecular dynamics calculations indicate that trans and cis photorexin adopt similar bent conformations and that the only discriminant between their structures and activities is the positioning of the N-terminus. This, in the case of the more active trans isomer, points towards the OX2 N-terminus and extra-cellular loop 2, a region of the receptor known to be involved in ligand binding and recognition consistent with a \"message-address\" system. Thus, our approach could be extended to several important families of endogenous peptides, such as endothelins, nociceptin, and dynorphins among others, that bind to their cognate receptors through a similar mechanism: a \"message\" domain involved in receptor activation and signal transduction, and an \"address\" sequence for receptor occupation and improved binding affinity.
摘要：
Orexinine能神经元与调节唤醒密切相关，觉醒,和食欲。他们的功能障碍与睡眠障碍有关，和非肽药物目前正在开发用于治疗失眠和发作性睡病。然而，没有光调节剂可以可逆地控制它们的活性。为了满足这种需要,设计了内源性神经兴奋性肽食欲素B的光开关肽类似物，合成，并在体外和体内进行了测试。该化合物-光食欲素-是针对食欲素受体报道的第一个光可逆配体。它可以在体外动态控制活性（包括与食欲素-B几乎相同的功效，高纳摩尔效力，和对人OX2受体的亚型选择性），并通过直接在水中施用在斑马鱼幼虫体内。光食欲素诱导运动的剂量和光依赖性变化，并减少与睡眠行为相关的连续感应反射。分子动力学计算表明，反式和顺式光食欲素采用相似的弯曲构象，并且它们的结构和活性之间的唯一区别是N末端的定位。这个,在更具活性的反式异构体的情况下，指向OX2N末端和细胞外环2，这是已知与配体结合和识别有关的受体区域，与“信息地址”系统一致。因此，我们的方法可以扩展到几个重要的内源性肽家族，如内皮素，痛觉肽,和强啡肽，通过类似的机制与它们的同源受体结合：参与受体激活和信号转导的“信息”域，以及受体占据和提高结合亲和力的“地址”序列。
