The Role of Arf4 in Sorting Photoreceptor Outer Segment Proteins

描述（由申请人提供）：我们的视觉的第一步发生在视网膜中，其中光在感光细胞的外段中被捕获。这种感光细胞器是独特的，因为它是一种经过修饰的初级纤毛，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索马中，随后通过离散的细胞内运输机制将其递送至外节。视色素视紫红质是外段膜中最丰富的蛋白质，其从ER/高尔基体到外段的靶向由小鸟嘌呤核苷酸结合蛋白Arf 4介导。虽然胞内定位和运输的视紫红质比任何其他光受体特异性蛋白质更好地理解，许多机制方面仍然不清楚，包括分子事件激活Arf 4启动视紫红质分选。与其他鸟嘌呤核苷酸结合蛋白一样，Arf 4预期在GDP/GTP交换时被激活。因此，我的建议的第一个目标是确定鸟嘌呤核苷酸交换因子，在光感受器中实现这一功能。我的第二个目标是确定Arf 4是否是唯一需要的， 视紫红质分选以及其他蛋白质是否依赖于Arf 4靶向外节。我还将探讨Arf 4可能参与其他细胞中纤毛细胞器的蛋白分选的假设。该项目对我们对病理生物学的一般理解具有广泛的意义。 遗传性视网膜变性是由影响光感受器外段蛋白质分选的突变引起的。

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.