Abstract：
Two retinal transcription factors, cone-rod homeobox (CRX) and neural retina leucine zipper (NRL), cooperate functionally and physically to control photoreceptor development and homeostasis. Mutations in CRX and NRL cause severe retinal diseases. Despite the roles of NRL and CRX, insight into their functions at the molecular level is lacking. Here, we have solved the crystal structure of the CRX homeodomain in complex with its cognate response element (Ret4) from the rhodopsin proximal promoter region. The structure reveals an unexpected 2:1 stoichiometry of CRX/Ret4 and unique orientation of CRX molecules on DNA, and it explains the mechanisms of pathogenic mutations in CRX. Mutations R41Q and E42K disrupt the CRX protein-protein contacts based on the structure and reduce the CRX/Ret4 binding stoichiometry, suggesting a novel disease mechanism. Furthermore, we show that NRL alters the stoichiometry and increases affinity of CRX binding at the rhodopsin promoter, which may enhance transcription of rod-specific genes and suppress transcription of cone-specific genes.
摘要：
两种视网膜转录因子，锥杆同源盒（CRX）和神经视网膜亮氨酸拉链（NRL），在功能和物理上进行合作以控制光感受器的发育和稳态。CRX和NRL中的突变导致严重的视网膜疾病。尽管NRL和CRX发挥了作用，缺乏在分子水平上对其功能的了解。这里,我们已经解决了CRX同源结构域的晶体结构及其来自视紫红质近端启动子区的同源反应元件（Ret4）。该结构揭示了CRX/Ret4的2：1化学计量和CRX分子在DNA上的独特取向，它解释了CRX致病突变的机制。突变R41Q和E42K基于结构破坏CRX蛋白-蛋白接触并降低CRX/Ret4结合化学计量,提示一种新的疾病机制。此外，我们表明，NRL改变化学计量和增加亲和力的CRX结合在视紫红质启动子，这可能会增强杆特异性基因的转录并抑制视锥特异性基因的转录。
