Control of the guanylate cyclase signaling unit in phototransduction by the RD3 protein

杆状和锥状光感受器细胞通过两种细胞内第二信使鸟苷-3′，5′-环单磷酸（环GMP）和钙的精细平衡内稳态运作。环GMP是由一种膜结合的鸟苷酸环化酶合成的，环GMP信号的失调可引起光感受器细胞的变性。几种形式的遗传性视网膜营养不良，如莱伯先天性黑朦、锥杆营养不良和视网膜色素变性，都与鸟苷酸环化酶及其调节蛋白GCAPs的基因突变有关。最近的证据表明，一种名为RD3的蛋白质通过控制其关键信号单位之一，鸟苷酸环化酶/ GCAP复合物，在维持光感受器功能方面起着至关重要的作用。本项目的目的是研究RD3蛋白如何与鸟苷酸环化酶的营养不良相关突变体相互作用，它是否稳定其中一些突变体的结构不稳定形式，以及它如何控制它们从内质网转运。此外，研究人员计划研究鸟苷酸环化酶激活剂GCAP1的组成型活性突变体是如何受到RD3蛋白共表达和关联的影响的。GCAP1会导致锥体营养不良。最后，RD3蛋白本身的分子和蛋白化学性质尚不清楚，该项目将进一步关注RD3和RD3突变体的结构-功能关系。在这个框架内，我们还将测试假设，如RD3磷酸化的翻译后修饰是否控制与环GMP信号单元的直接相互作用。我们期望从我们的研究中更深入地了解导致视网膜变性的分子机制，包括RD3蛋白及其与鸟苷酸环化酶复合物的相互依赖性。

Rod and cone photoreceptor cells operate by a fine-balanced homeostasis of two intracellular second messengers, guanosine-3´,5´-cyclic monophosphate (cyclic GMP) and calcium. Cyclic GMP is synthesized by a membrane bound guanylate cyclase and dysregulation of cyclic GMP signaling can cause degeneration of photoreceptor cells. Several forms of hereditary retinal dystrophies like Leber congenital amaurosis, cone-rod dystrophies and retinitis pigmentosa correlate with mutations in the genes of guanylate cyclase and its regulatory proteins named GCAPs. Recent evidence suggests that a protein named RD3 has a crucial role in maintaining photoreceptor function by controlling one of its key signaling units, the guanylate cyclase/ GCAP complex. The aim of the present project is to investigate how the RD3 protein interacts with dystrophy relevant mutants of guanylate cyclase, whether it stabilizes structurally labile forms of some of these mutants, and how it controls their trafficking out of the endoplasmic reticulum. Furthermore, it is planned to investigate how constitutively active mutants of the guanylate cyclase activator GCAP1, which cause cone dystrophies, are influenced by co-expression of and association with the RD3 protein. Finally, the molecular and protein-chemical properties of the RD3 protein itself are not well understood and the project will further focus on structure-function relationships of RD3 and RD3 mutants. Within this framework we will also test the hypothesis, whether a posttranslational modification like phosphorylation of RD3 controls the direct interaction with the cyclic GMP signaling unit. We expect from our studies a deeper understanding of the molecular mechanisms leading to retinal degeneration involving the RD3 protein and its mutual dependencies with the guanylate cyclase complex.