Crystal structure of a Ca2+-discharged photoprotein -: Implications for mechanisms of the calcium trigger and bioluminescence
Crystal structure of a Ca2+-discharged photoprotein -: Implications for mechanisms of the calcium trigger and bioluminescence
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DOI：
10.1074/jbc.m402427200
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发表时间：
2004-08-06
影响因子：
4.8
通讯作者：
Wang, BC
中科院分区：
文献类型：
--
作者：
Deng, L;Markova, SV;Wang, BC
Ca2+ 调节发光蛋白是 EF-hand 钙结合蛋白家族的成员。添加 Ca2+ 会引发蛋白质结合的氢过氧腔肠素的脱羧反应，从而形成激发态的产物腔肠酰胺，从而产生蓝色生物发光。基于水母发光蛋白和几种奥贝林蛋白的空间结构，我们假设了 Ca2+ 触发机制以及不同激发态生成的机制，这些激发态是不同颜色生物发光的起源。在这里，我们以 1.96 埃的分辨率报道了 Ca2+ 放电发光蛋白 obelin 的晶体结构。结果为所提出的机制提供了支持，并为这些过程的细节提供了新的结构见解。由 Ca2+ 关联引起的整体构象变化是 EF-hand 蛋白超家族中钙信号调节剂类别的典型。 Ca2+ 离子进入 EF 手环的适应会传播到现在被腔肠酰胺占据的蛋白质的活性位点，其中 His-175 咪唑环发生显着的重新定位和翻转，这在触发假设中至关重要。此外，活性发光蛋白中发现的 His-22 和腔肠素之间的氢键保留在腔肠酰胺的等效位置，证实了所提出的快速激发态质子转移，这将导致酚盐离子对的激发态，从而导致生物发光的蓝色发射。
Ca2+-regulated photoproteins are members of the EF-hand calcium-binding protein family. The addition of Ca2+ produces a blue bioluminescence by triggering a decarboxylation reaction of protein-bound hydroperoxycoelenterazine to form the product, coelenteramide, in an excited state. Based on the spatial structures of aequorin and several obelins, we have postulated mechanisms for the Ca2+ trigger and for generation of the different excited states that are the origin of the different colors of bioluminescence. Here we report the crystal structure of the Ca2+-discharged photoprotein obelin at 1.96-Angstrom resolution. The results lend support to the proposed mechanisms and provide new structural insight into details of these processes. Global conformational changes caused by Ca2+ association are typical of the class of calcium signal modulators within the EF-hand protein superfamily. Accommodation of the Ca2+ ions into the loops of the EF-hands is seen to propagate into the active site of the protein now occupied by the coelenteramide where there is a significant repositioning and flipping of the His-175 imidazole ring as crucially required in the trigger hypothesis. Also the H-bonding between His-22 and the coelenterazine found in the active photoprotein is preserved at the equivalent position of coelenteramide, confirming the proposed rapid excited state proton transfer that would lead to the excited state of the phenolate ion pair, which is responsible for the blue emission of bioluminescence.