Stephen Ricardo, Bereta Grzegorz, Golczak Marcin, Palczewski Krzysztof, Sousa Marcelo Carlos
Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO 80309, USA.
Structure. 2007 Nov;15(11):1392-402. doi: 10.1016/j.str.2007.09.013.
Guanylate cyclase-activating proteins (GCAPs) are Ca(2+)-binding proteins myristoylated at the N terminus that regulate guanylate cyclases in photoreceptor cells and belong to the family of neuronal calcium sensors (NCS). Many NCS proteins display a recoverin-like "calcium-myristoyl switch" whereby the myristoyl group, buried inside the protein in the Ca(2+)-free state, becomes fully exposed upon Ca(2+) binding. Here we present a 2.0 A resolution crystal structure of myristoylated GCAP1 with Ca(2+) bound. The acyl group is buried inside Ca(2+)-bound GCAP1. This is in sharp contrast to Ca(2+)-bound recoverin, where the myristoyl group is solvent exposed. Furthermore, we provide direct evidence that the acyl group in GCAP1 remains buried in the Ca(2+)-free state and does not undergo switching. A pronounced kink in the C-terminal helix and the presence of the myristoyl group allow clustering of sequence elements crucial for GCAP1 activity.
鸟苷酸环化酶激活蛋白（GCAPs）是一类在N端进行了肉豆蔻酰化修饰的钙结合蛋白，它们在光感受器细胞中调节鸟苷酸环化酶，属于神经元钙传感器（NCS）家族。许多NCS蛋白表现出一种类恢复蛋白的“钙-肉豆蔻酰开关”，即肉豆蔻酰基团在无钙状态下埋于蛋白内部，在结合钙离子后会完全暴露。在此，我们展示了结合钙离子的肉豆蔻酰化GCAP1的2.0埃分辨率晶体结构。酰基埋于结合钙离子的GCAP1内部。这与结合钙离子的恢复蛋白形成鲜明对比，在恢复蛋白中肉豆蔻酰基团暴露于溶剂中。此外，我们提供了直接证据表明GCAP1中的酰基在无钙状态下仍被埋于内部，并未发生开关变化。C端螺旋中的一个明显扭结以及肉豆蔻酰基团的存在使得对GCAP1活性至关重要的序列元件得以聚集。
