Crystal structure of metarhodopsin II
Crystal structure of metarhodopsin II
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DOI：
10.1038/nature09789
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发表时间：
2011-03-31
期刊：
影响因子：
64.8
通讯作者：
Ernst, Oliver P.
中科院分区：
文献类型：
--
作者：
Choe, Hui-Woog;Kim, Yong Ju;Ernst, Oliver P.
G蛋白偶联受体(GPCRs)是七种跨膜螺旋(TM)蛋白，通过结合细胞外配体和偶联细胞内异源三聚体G蛋白(Gαβγ)(1)，将信号传递到活细胞内。光感受器视紫红质偶联到转导蛋白，并带有其配体11-顺式视网膜，通过质子化的席夫碱与视蛋白载脂蛋白(2)共价结合。一个光子的吸收会导致视网膜顺反异构化，并在原位产生激动剂全反式视网膜。早期的感光产物形成了活性的G蛋白结合中间体变紫红质II(Meta II)，其中视网膜Schiff碱基仍然完整但去质子化。质子从Schiff碱基上解离，打破了蛋白质中的一个主要限制，并使进一步的激活步骤成为可能，包括TM6的向外倾斜和形成一个大的细胞质缝隙，以摄取Gα亚单位(3-5)相互作用的C末端。由于席夫碱的水解，Meta II的寿命很短，而且出了名的难以结晶。因此，我们用全反式视网膜浸泡视素晶体形成Meta II，推测晶体中高浓度的视蛋白以活性构象(Ops*)(6，7)可能促进全反式视网膜摄取和席夫碱的形成。在这里，我们分别给出了Meta II单独的和与来自Gα的11个氨基酸的C末端片段(GαCT2)形成的络合物的3.0埃和2.85埃的晶体结构。GαCT2结合在细胞质一侧的一个大缝隙中，类似于类似的Gα衍生多肽与Ops*的结合(参考文献2)。7)。在Meta II结构中，来自视网膜配体的电子密度无缝地进入Lys 296侧链，反映了Schiff碱键的正确形成。视网膜是一种松弛的构象，与纯晶体全视网膜相比几乎没有扭曲。通过与早期光产品的比较，我们提出了视网膜移位和旋转是如何引起Meta II特有的整体构象变化的。这些结构现在可以作为GPCR大家族的模型。
G-protein-coupled receptors (GPCRs) are seven transmembrane helix (TM) proteins that transduce signals into living cells by binding extracellular ligands and coupling to intracellular heterotrimeric Gproteins (G alpha beta gamma)(1). The photoreceptor rhodopsin couples to transducin and bears its ligand 11-cis-retinal covalently bound via a protonated Schiff base to the opsin apoprotein(2). Absorption of a photon causes retinal cis/trans isomerization and generates the agonist all-trans-retinal in situ. After early photoproducts, the active G-protein-binding intermediate metarhodopsin II (Meta II) is formed, in which the retinal Schiff base is still intact but deprotonated. Dissociation of the proton from the Schiff base breaks a major constraint in the protein and enables further activating steps, including an outward tilt of TM6 and formation of a large cytoplasmic crevice for uptake of the interacting C terminus of the G alpha subunit(3-5). Owing to Schiff base hydrolysis, Meta II is short-lived and notoriously difficult to crystallize. We therefore soaked opsin crystals with all-trans-retinal to form Meta II, presuming that the crystal's high concentration of opsin in an active conformation (Ops*)(6,7) may facilitate all-trans-retinal uptake and Schiff base formation. Here we present the 3.0 angstrom and 2.85 angstrom crystal structures, respectively, of Meta II alone or in complex with an 11-amino-acid C-terminal fragment derived from G alpha (G alpha CT2). G alpha CT2 binds in a large crevice at the cytoplasmic side, akin to the binding of a similar G alpha-derived peptide to Ops* (ref. 7). In the Meta II structures, the electron density from the retinal ligand seamlessly continues into the Lys 296 side chain, reflecting proper formation of the Schiff base linkage. The retinal is in a relaxed conformation and almost undistorted compared with pure crystalline all-trans-retinal. By comparison with early photoproducts we propose how retinal translocation and rotation induce the gross conformational changes characteristic for Meta II. The structures can now serve as models for the large GPCR family.