The Role of Arf4 in Sorting Photoreceptor Outer Segment Proteins

描述(申请人提供)：我们视觉的第一步发生在视网膜，光线在感光细胞的外层被捕获。这种感光细胞器的独特之处在于，它是一种改良的初级纤毛，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转运机制将它们输送到外段。视紫红质是外节膜中含量最丰富的蛋白质，其靶向从内质网/高尔基体到外节是由一个小的鸟嘌呤核苷酸结合蛋白Arf4介导的。虽然视紫红质在细胞内的靶向和运输比任何其他光感受器特异性蛋白都更好地被理解，但许多机制方面仍然不清楚，包括激活Arf4启动视紫红质分选的分子事件。与其他鸟嘌呤核苷酸结合蛋白一样，Arf4有望在GDP/GTP交换时被激活。因此，我的建议的第一个目的是确定在光感受器中实现这一功能的鸟核苷酸交换因子。我的第二个目标是确定Arf4是否是 视紫红质分类，以及其他蛋白质是否依赖Arf4靶向外层片段。我还将探讨Arf4可能参与了对其他细胞中纤毛细胞器的蛋白质分选的假设。这个项目对于我们对病理生物学的一般理解具有广泛的意义 处理遗传性视网膜退化的潜在病例，这是由影响蛋白质分选到光感受器外段的突变引起的。

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.