Porter J A, Minke B, Montell C
Department of Biological Chemistry, Johns Hopkins University, School of Medicine, Baltimore, MD 21205, USA.
EMBO J. 1995 Sep 15;14(18):4450-9. doi: 10.1002/j.1460-2075.1995.tb00124.x.
The ninaC locus encodes two unconventional myosins, p132 and p174, consisting of fused protein kinase and myosin head domains expressed in Drosophila photoreceptor cells. NinaC are the major calmodulin-binding proteins in the retina and the NinaC-calmodulin interaction is required for the normal subcellular localization of calmodulin as well as for normal photo-transduction. In the current report, we present evidence for two calmodulin-binding sites in NinaC, C1 and C2, which have different in vitro binding properties. C1 was found to be common to both p132 and p174 while C2 was unique to p174. To address the requirements for calmodulin binding at each site in vivo, we generated transgenic flies expressing ninaC genes deleted for either C1 or C2. We found that the spatial localization of calmodulin depended on binding to both C1 and C2. Furthermore, mutation of either site resulted in a defective photoresponse. A prolonged depolarization afterpotential (PDA) was elicited at lower light intensities than necessary to produce a PDA in wild-type flies. These results suggest that calmodulin binding to both C1 and C2 is required in vivo for termination of phototransduction.
ninaC基因座编码两种非常规肌球蛋白，即p132和p174，它们由融合的蛋白激酶和肌球蛋白头部结构域组成，在果蝇光感受器细胞中表达。NinaC是视网膜中主要的钙调蛋白结合蛋白，NinaC与钙调蛋白的相互作用对于钙调蛋白正常的亚细胞定位以及正常的光转导是必需的。在本报告中，我们提供了NinaC中两个钙调蛋白结合位点C1和C2的证据，它们具有不同的体外结合特性。发现C1是p132和p174共有的，而C2是p174特有的。为了研究体内每个位点钙调蛋白结合的需求，我们构建了表达缺失C1或C2的ninaC基因的转基因果蝇。我们发现钙调蛋白的空间定位取决于与C1和C2的结合。此外，任何一个位点的突变都会导致光反应缺陷。在比野生型果蝇产生延长去极化后电位（PDA）所需的光强度更低时，就会引发延长的去极化后电位。这些结果表明，体内光转导的终止需要钙调蛋白与C1和C2两者结合。
