Huber A, Sander P, Gobert A, Bähner M, Hermann R, Paulsen R
Zoological Institute I, University of Karlsruhe, Germany.
EMBO J. 1996 Dec 16;15(24):7036-45.
The transient receptor potential protein (Trp) is a putative capacitative Ca2+ entry channel present in fly photoreceptors, which use the inositol 1,4,5-trisphosphate (InsP3) signaling pathway for phototransduction. By immunoprecipitation studies, we find that Trp is associated into a multiprotein complex with the norpA-encoded phospholipase C, an eye-specific protein kinase C (InaC) and with the InaD protein (InaD). InaD is a putative substrate of InaC and contains two PDZ repeats, putative protein-protein interaction domains. These proteins are present in the photoreceptor membrane at about equimolar ratios. The Trp homolog analyzed here is isolated together with NorpA, InaC and InaD from blowfly (Calliphora) photoreceptors. Compared to Drosophila Trp, the Calliphora Trp homolog displays 77% amino acid identity. The highest sequence conservation is found in the region that contains the putative transmembrane domains S1-S6 (91% amino acid identity). As investigated by immunogold labeling with specific antibodies directed against Trp and InaD, the Trp signaling complex is located in the microvillar membranes of the photoreceptor cells. The spatial distribution of the signaling complex argues against a direct conformational coupling of Trp to an InsP3 receptor supposed to be present in the membrane of internal photoreceptor Ca2+ stores. It is suggested that the organization of signal transducing proteins into a multiprotein complex provides the structural basis for an efficient and fast activation and regulation of Ca2+ entry through the Trp channel.
瞬时受体电位蛋白（Trp）是一种推测存在于果蝇光感受器中的电容性Ca2+内流通道，果蝇光感受器利用肌醇1,4,5-三磷酸（InsP3）信号通路进行光转导。通过免疫沉淀研究，我们发现Trp与norpa编码的磷脂酶C、一种眼特异性蛋白激酶C（InaC）以及InaD蛋白（InaD）结合形成多蛋白复合物。InaD是InaC的推测底物，包含两个PDZ重复序列，即推测的蛋白质-蛋白质相互作用结构域。这些蛋白质以大约等摩尔比存在于光感受器膜中。本文分析的Trp同源物是从丽蝇（Calliphora）光感受器中与NorpA、InaC和InaD一起分离得到的。与果蝇Trp相比，丽蝇Trp同源物显示出77%的氨基酸同一性。在包含推测的跨膜结构域S1-S6的区域中发现了最高的序列保守性（91%的氨基酸同一性）。用针对Trp和InaD的特异性抗体进行免疫金标记研究表明，Trp信号复合物位于光感受器细胞的微绒毛膜中。信号复合物的空间分布与Trp与推测存在于内部光感受器Ca2+储存膜中的InsP3受体的直接构象偶联相矛盾。有人提出，将信号转导蛋白组织成多蛋白复合物为通过Trp通道高效快速地激活和调节Ca2+内流提供了结构基础。
