The GTP- and Phospholipid-Binding Protein TTD14 Regulates Trafficking of the TRPL Ion Channel in Drosophila Photoreceptor Cells.
The GTP- and Phospholipid-Binding Protein TTD14 Regulates Trafficking of the TRPL Ion Channel in Drosophila Photoreceptor Cells.
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DOI：
10.1371/journal.pgen.1005578
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发表时间：
2015-10
期刊：
影响因子：
4.5
通讯作者：
Huber A
中科院分区：
文献类型：
--
作者：
Cerny AC;Altendorfer A;Schopf K;Baltner K;Maag N;Sehn E;Wolfrum U;Huber A
信号蛋白的再循环是多种信号通路中的常见现象。在果蝇的光感受器中，视紫红质的光吸收触发磷脂酶Cβ介导的离子通道瞬时受体电位（TRP）和TRP样（TRPL）的开放，并产生视觉反应。这些信号蛋白位于一个被称为横纹肌的质膜区室中。主要视紫红质（Rh1）和TRP主要定位于横纹肌中的光和黑暗。相比之下，TRPL在黑暗中的横纹肌质膜和光照下的细胞体中的储存室之间易位，在随后的黑暗适应中，TRPL可以从那里再循环到质膜。在这里，我们确定了突变的基因在trpl易位缺陷14（ttd14），这是所需的TRPL内化从横纹肌在光和TRPL循环回到横纹肌在黑暗中。TTD14在无脊椎动物中高度保守，并在体外结合GTP。ttd14突变改变了GTP结合结构域中保守的脯氨酸残基（P75 L），并取消了与GTP的结合。这表明GTP结合对于TTD 14功能是必需的。TTD 14是一种胞质蛋白，与PtdIns（3）P（一种富含早期内体膜的脂质）和磷脂酸结合。与TRPL相反，在ttd14 P75L突变体中，膜蛋白Rh1和TRP的横纹肌定位不受影响。ttd14 P75L突变导致Rh1非依赖性光感受器退化和幼虫致死，这表明其他过程也受到ttd14 P75L突变的影响。总之，TTD 14是TRPL运输的新型调节剂，参与TRPL的内化和随后的分选进入使该离子通道能够返回质膜的再循环途径。神经元中的蛋白质运输发生在细胞的整个寿命中，并且包括质膜蛋白的内化和再分布。受调节的蛋白质运输控制具有受体和离子通道的质膜的装备，从而减弱或增强神经元功能。质膜蛋白再循环的缺陷会导致有害的神经退行性疾病，如阿尔茨海默病、帕金森病和唐氏综合征。在果蝇光感受器中，TRPL离子通道与TRP通道一起介导视觉，并且光依赖性地在内膜储存室和顶端质膜之间穿梭。在这里，我们报告的ttd14基因的突变，抑制TRPL贩运在两个方向，也导致光感受器变性的鉴定。TTD 14蛋白含有与PX结构域具有弱同源性的区域，其也存在于在内体中分选货物并使蛋白质循环的蛋白质中。我们将TTD 14描述为一种新的感光细胞维持和离子通道运输的调节剂，它与GTP和PtdIns（3）P（一种在早期内体中富集的磷脂）结合。
Recycling of signaling proteins is a common phenomenon in diverse signaling pathways. In photoreceptors of Drosophila, light absorption by rhodopsin triggers a phospholipase Cβ-mediated opening of the ion channels transient receptor potential (TRP) and TRP-like (TRPL) and generates the visual response. The signaling proteins are located in a plasma membrane compartment called rhabdomere. The major rhodopsin (Rh1) and TRP are predominantly localized in the rhabdomere in light and darkness. In contrast, TRPL translocates between the rhabdomeral plasma membrane in the dark and a storage compartment in the cell body in the light, from where it can be recycled to the plasma membrane upon subsequent dark adaptation. Here, we identified the gene mutated in trpl translocation defective 14 (ttd14), which is required for both TRPL internalization from the rhabdomere in the light and recycling of TRPL back to the rhabdomere in the dark. TTD14 is highly conserved in invertebrates and binds GTP in vitro. The ttd14 mutation alters a conserved proline residue (P75L) in the GTP-binding domain and abolishes binding to GTP. This indicates that GTP binding is essential for TTD14 function. TTD14 is a cytosolic protein and binds to PtdIns(3)P, a lipid enriched in early endosome membranes, and to phosphatidic acid. In contrast to TRPL, rhabdomeral localization of the membrane proteins Rh1 and TRP is not affected in the ttd14 P75L mutant. The ttd14 P75L mutation results in Rh1-independent photoreceptor degeneration and larval lethality suggesting that other processes are also affected by the ttd14 P75L mutation. In conclusion, TTD14 is a novel regulator of TRPL trafficking, involved in internalization and subsequent sorting of TRPL into the recycling pathway that enables this ion channel to return to the plasma membrane. Protein trafficking in neurons occurs throughout the lifetime of a cell and includes the internalization and redistribution of plasma membrane proteins. Regulated protein trafficking controls the equipment of the plasma membrane with receptors and ion channels and thereby attenuates or enhances neuronal function. Defects in recycling of plasma membrane proteins can cause detrimental neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and Down´s syndrome. In Drosophila photoreceptors, the TRPL ion channel, together with the TRP channel, mediates vision and light-dependently shuttles between an endomembrane storage compartment and the apical plasma membrane. Here, we report the identification of a mutation in the ttd14 gene that inhibits TRPL-trafficking in both directions and also results in photoreceptor degeneration. The TTD14 protein contains a region with weak homology to a PX-domain, which is also found in proteins that sort cargo in the endosome and enable protein recycling. We characterize TTD14 as a new regulator of photoreceptor maintenance and ion channel trafficking that binds to GTP and PtdIns(3)P, a phospholipid enriched in early endosomes.