Xu X Z, Wes P D, Chen H, Li H S, Yu M, Morgan S, Liu Y, Montell C
Departments of Biological Chemistry and Neuroscience, The Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205, USA.
J Biol Chem. 1998 Nov 20;273(47):31297-307. doi: 10.1074/jbc.273.47.31297.
Ca2+ influxes regulate multiple events in photoreceptor cells including phototransduction and synaptic transmission. An important Ca2+ sensor in Drosophila vision appears to be calmodulin since a reduction in levels of retinal calmodulin causes defects in adaptation and termination of the photoresponse. These functions of calmodulin appear to be mediated, at least in part, by four previously identified calmodulin-binding proteins: the TRP and TRPL ion channels, NINAC and INAD. To identify additional calmodulin-binding proteins that may function in phototransduction and/or synaptic transmission, we conducted a screen for retinal calmodulin-binding proteins. We found eight additional calmodulin-binding proteins that were expressed in the Drosophila retina. These included six targets that were related to proteins implicated in synaptic transmission. Among these six were a homolog of the diacylglycerol-binding protein, UNC13, and a protein, CRAG, related to Rab3 GTPase exchange proteins. Two other calmodulin-binding proteins included Pollux, a protein with similarity to a portion of a yeast Rab GTPase activating protein, and Calossin, an enormous protein of unknown function conserved throughout animal phylogeny. Thus, it appears that calmodulin functions as a Ca2+ sensor for a broad diversity of retinal proteins, some of which are implicated in synaptic transmission.
钙离子内流调节光感受器细胞中的多种事件，包括光转导和突触传递。在果蝇视觉中，一种重要的钙离子传感器似乎是钙调蛋白，因为视网膜钙调蛋白水平的降低会导致光反应适应和终止方面的缺陷。钙调蛋白的这些功能似乎至少部分是由四种先前鉴定的钙调蛋白结合蛋白介导的：TRP和TRPL离子通道、NINAC和INAD。为了鉴定可能在光转导和/或突触传递中起作用的其他钙调蛋白结合蛋白，我们对视网膜钙调蛋白结合蛋白进行了筛选。我们发现了另外八种在果蝇视网膜中表达的钙调蛋白结合蛋白。其中包括六个与参与突触传递的蛋白质相关的靶点。这六个靶点中有一个二酰基甘油结合蛋白UNC13的同源物，以及一个与Rab3 GTPase交换蛋白相关的蛋白质CRAG。另外两个钙调蛋白结合蛋白包括Pollux，一种与酵母Rab GTPase激活蛋白的一部分相似的蛋白质，以及Calossin，一种在整个动物系统发育中保守的功能未知的巨大蛋白质。因此，钙调蛋白似乎作为多种视网膜蛋白的钙离子传感器发挥作用，其中一些与突触传递有关。
