Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine, Case Western Reserve University, Cleveland, OH 44195, USA.
Int J Mol Sci. 2021 Jul 28;22(15):8066. doi: 10.3390/ijms22158066.
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.
光感受器是高度分隔的细胞，在内节 (IS) 中大量合成蛋白质，并运输到外节 (OS) 和突触末端。Tulp1 是一种定位于 IS 和突触的光感受器特异性蛋白。在缺乏 Tulp1 的情况下，几种 OS 特异性蛋白质被错误定位，突触囊泡再循环受损。为了更好地理解 Tulp1 在蛋白质运输中的作用，我们在当前研究中的方法是通过对视网膜进行连续切线切片，物理分离含 Tulp1 的光感受器隔室，并通过免疫沉淀和液相色谱串联质谱鉴定隔室特异性的 Tulp1 结合伴侣。我们的结果表明 Tulp1 具有两个不同的相互作用组。我们报告了以下发现：（1）Tulp1 与动力蛋白家族成员 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，以及（3）Tulp1 与微管相关蛋白 1B (MAP1B) 之间的相互作用在两个隔室中。在野生型视网膜中的免疫定位研究表明，Tulp1 及其结合伴侣共同定位于各自的隔室。我们的观察结果与 Tulp1 在多个光感受器隔室中的蛋白质运输中起作用的观点一致，可能作为一种衔接分子将囊泡与分子马达和细胞骨架支架连接起来。
