Crystal structure of squid rhodopsin
Crystal structure of squid rhodopsin
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DOI：
10.1038/nature06925
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发表时间：
2008-05-15
期刊：
影响因子：
64.8
通讯作者：
Kouyama, Tsutomu
中科院分区：
文献类型：
--
作者：
Murakami, Midori;Kouyama, Tsutomu
无脊椎动物光转导使用肌醇-1，4，5-三磷酸信号级联，其中光活化的视紫红质刺激G（q）型G蛋白，即刺激膜结合磷脂酶C β的一类G蛋白。许多G蛋白偶联受体使用相同的级联反应，表明无脊椎动物视紫红质是一个原型成员。在这里，我们以2.5埃的分辨率报告了鱿鱼（太平洋褶裥鱼）视紫红质的晶体结构。在七个跨膜α-螺旋中，螺旋V和VI延伸到细胞质介质中，并且与两个细胞质螺旋一起，它们从膜表面形成刚性突起。这种在牛视紫红质中没有的特殊结构似乎对G（q）型G蛋白的识别至关重要。视黄酸席夫碱与天冬酰胺87或酪氨酸111形成氢键;它远离假定的谷氨酸180。在晶体中，相邻单体的氨基末端多肽之间形成紧密的关联;这种膜间二聚化可能是负责在感光体横纹中六角包装的微绒毛膜的组织。
Invertebrate phototransduction uses an inositol-1,4,5-trisphosphate signalling cascade in which photoactivated rhodopsin stimulates a G(q)-type G protein, that is, a class of G protein that stimulates membrane-bound phospholipase C beta. The same cascade is used by many G-protein-coupled receptors, indicating that invertebrate rhodopsin is a prototypical member. Here we report the crystal structure of squid (Todarodes pacificus) rhodopsin at 2.5 angstrom resolution. Among seven transmembrane alpha-helices, helices V and VI extend into the cytoplasmic medium and, together with two cytoplasmic helices, they form a rigid protrusion from the membrane surface. This peculiar structure, which is not seen in bovine rhodopsin, seems to be crucial for the recognition of G(q)-type G proteins. The retinal Schiff base forms a hydrogen bond to Asn 87 or Tyr 111; it is far from the putative counterion Glu 180. In the crystal, a tight association is formed between the amino-terminal polypeptides of neighbouring monomers; this intermembrane dimerization may be responsible for the organization of hexagonally packed microvillar membranes in the photoreceptor rhabdom.