The Role of Arf4 in Sorting Photoreceptor Outer Segment Proteins

描述（由申请人提供）：我们视觉的第一步发生在视网膜上，光在感光细胞的外部部分被捕获。这种光感应细胞器的独特之处在于它是一种修饰的初级纤毛，集中了参与视觉信号转导的蛋白质。这些蛋白质的合成发生在细胞体中，然后通过离散的细胞内运输机制将它们传递到外段。视色素紫红质是外节膜上最丰富的蛋白，其从内质网/高尔基体向外节的靶向是由一个小鸟嘌呤核苷酸结合蛋白Arf4介导的。尽管人们对视紫红质的细胞内靶向和运输比其他任何光受体特异性蛋白都了解得更好，但许多机制方面仍不清楚，包括激活Arf4启动视紫红质的分子事件。与其他鸟嘌呤核苷酸结合蛋白一样，Arf4预计在GDP/GTP交换时被激活。因此，我建议的第一个目标是确定在光感受器中实现这一功能的鸟嘌呤核苷酸交换因子。我的第二个目标是确定Arf4是否是唯一需要的

DESCRIPTION (provided by applicant): The first step of our vision takes place in the retina where light is captured in the outer segment of photoreceptor cells. This light-sensing organelle is unique in that it is a modified primary cilium that is concentrated with proteins involved in visual signal transduction. Synthesis of these proteins occurs in the cell soma, followed by their delivery to the outer segment by discrete intracellular trafficking mechanisms. The visual pigment rhodopsin is the most abundant protein of the outer segment membranes and its targeting from the ER/Golgi to the outer segments is mediated by a small guanine nucleotide-binding protein Arf4. Though intracellular targeting and trafficking of rhodopsin is understood better than any other photoreceptor-specific protein, many mechanistic aspects remain unclear including the molecular event activating Arf4 to initiate rhodopsin sorting. As other guanine nucleotide-binding proteins, Arf4 is expected to be activated upon GDP/GTP exchange. Thus the first aim of my proposal is to determine the guanine nucleotide exchange factor that fulfills this function in photoreceptors. My second aim is to identify whether Arf4 is uniquely required for rhodopsin sorting and whether other proteins rely on Arf4 for targeting to the outer segments. I will also explore the hypothesis that Arf4 may be engaged in protein sorting to ciliary organelles in other cells. This project has broad implication for our general understanding of pathobiological processes underlying cases of inherited retinal degenerations, which are caused by mutations affecting protein sorting to the outer segment of photoreceptors.