The crystal structure of GCAP3 suggests molecular mechanism of GCAP-linked cone dystrophies.
The crystal structure of GCAP3 suggests molecular mechanism of GCAP-linked cone dystrophies.
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DOI：
10.1016/j.jmb.2006.03.042
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发表时间：
2006-06
影响因子：
5.6
通讯作者：
R. Stephen;K. Palczewski;M. Sousa
中科院分区：
文献类型：
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作者：
R. Stephen;K. Palczewski;M. Sousa
视觉色素对光的吸收启动光导途径，导致细胞内循环gmp （cGMP）池的降解。这种水解促进cgmp门控阳离子通道的关闭，从而导致杆状和锥状感光细胞膜的超极化。鸟苷酸环化酶激活蛋白（GCAPs）是一个以Ca2+依赖的方式调节视网膜鸟苷酸环化酶（GC）活性的蛋白家族。在高[Ca2+]，典型的暗适应状态（~ 500nM）下，GCAPs抑制视网膜GCs。在关闭cGMP门控通道后发生的低[Ca2+] (~ 50nM)， GCAPs激活视网膜GCs以补充暗态cGMP水平。在这里，我们报告了Ca2+结合的未肉豆酰化的人GCAP3的晶体结构。GCAP3是EF-hand Ca2+结合蛋白，Ca2+与EF2、3和4结合，而Ca2+与EF-hand 1的结合是禁用的。GCAP3包含两个结构域，其EF-hand基序以类似于GCAP2的串联阵列排列，并且是Ca2+结合蛋白的恢复蛋白亚家族成员。残基不参与Ca2+结合，但在所有gcap中都是保守的，在n端结构域聚集在EF1周围，可能代表了与GCs的界面。密切相关的GCAP1的五个点突变与锥体营养不良的病因有关。这些残基在GCAP3中是保守的，其结构表明这些氨基酸具有重要的作用。我们提出了一个基于GCAP3的GCAP1同源模型，该模型提供了对GCAP1突变产生的常染色体显性锥体营养不良的分子机制的见解。
Absorption of light by visual pigments initiates the phototransduction pathway that results in degradation of the intracellular pool of cyclic-GMP (cGMP). This hydrolysis promotes the closing of cGMP-gated cation channels and consequent hyperpolarization of rod and cone photoreceptor cell membranes. Guanylate cyclase-activating proteins (GCAPs) are a family of proteins that regulate retinal guanylate cyclase (GC) activity in a Ca2+-dependent manner. At high [Ca2+], typical of the dark–adapted state (∼500nM), GCAPs inhibit retinal GCs. At the low [Ca2+] (∼50nM) that occurs after the closing of cGMP-gated channels, GCAPs activate retinal GCs to replenish dark-state cGMP levels. Here, we report the crystal structure of unmyristoylated human GCAP3 with Ca2+bound. GCAP3 is an EF-hand Ca2+-binding protein with Ca2+bound to EF2, 3 and 4, while Ca2+binding to EF-hand 1 is disabled. GCAP3 contains two domains with the EF-hand motifs arranged in a tandem array similar to GCAP2 and members of the recoverin subfamily of Ca2+-binding proteins. Residues not involved in Ca2+binding, but conserved in all GCAPs, cluster around EF1 in the N-terminal domain and may represent the interface with GCs. Five point mutations in the closely related GCAP1 have been linked to the etiology of cone dystrophies. These residues are conserved in GCAP3 and the structure suggests important roles for these amino acids. We present a homology model of GCAP1 based on GCAP3 that offers insight into the molecular mechanism underlying the autosomal dominant cone dystrophies produced by GCAP1 mutations.