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Abstract：
Photoreceptors are highly compartmentalized cells with large amounts of proteins synthesized in the inner segment (IS) and transported to the outer segment (OS) and synaptic terminal. Tulp1 is a photoreceptor-specific protein localized to the IS and synapse. In the absence of Tulp1, several OS-specific proteins are mislocalized and synaptic vesicle recycling is impaired. To better understand the involvement of Tulp1 in protein trafficking, our approach in the current study was to physically isolate Tulp1-containing photoreceptor compartments by serial tangential sectioning of retinas and to identify compartment-specific Tulp1 binding partners by immunoprecipitation followed by liquid chromatography tandem mass spectrometry. Our results indicate that Tulp1 has two distinct interactomes. We report the identification of: (1) an IS-specific interaction between Tulp1 and the motor protein Kinesin family member 3a (Kif3a), (2) a synaptic-specific interaction between Tulp1 and the scaffold protein Ribeye, and (3) an interaction between Tulp1 and the cytoskeletal protein microtubule-associated protein 1B (MAP1B) in both compartments. Immunolocalization studies in the wild-type retina indicate that Tulp1 and its binding partners co-localize to their respective compartments. Our observations are compatible with Tulp1 functioning in protein trafficking in multiple photoreceptor compartments, likely as an adapter molecule linking vesicles to molecular motors and the cytoskeletal scaffold.
摘要：
光感受器是高度区隔化的细胞,其具有在内部区段(IS)中合成的大量蛋白质并被转运到外部区段(OS)和突触末端。Tulp1是位于IS和突触的光感受器特异性蛋白。在不存在Tulp1的情况下，几种OS特异性蛋白被错误定位，突触小泡再循环受损。为了更好地了解Tulp1在蛋白质贩运中的参与，在本研究中,我们的方法是通过连续切向视网膜切片物理分离含Tulp1的光感受器区室,并通过免疫沉淀和液相色谱串联质谱法鉴定区室特异性Tulp1结合配偶体.我们的结果表明，Tulp1具有两个不同的相互作用。我们报告了以下鉴定：（1）Tulp1与运动蛋白Kinesin家族成员3a（Kif3a）之间的IS特异性相互作用，（2）Tulp1与支架蛋白Ribeye之间的突触特异性相互作用，和（3）两个区室中Tulp1与细胞骨架蛋白微管相关蛋白1B（MAP1B）之间的相互作用。野生型视网膜中的免疫定位研究表明Tulp1及其结合配偶体共定位到它们各自的区室。我们的观察结果与Tulp1在多个光感受器隔室中蛋白质运输中的功能兼容，可能是连接囊泡与分子马达和细胞骨架支架的衔接分子。
