High resolution structure of Deinococcus bacteriophytochrome yields new insights into phytochrome architecture and evolution
High resolution structure of Deinococcus bacteriophytochrome yields new insights into phytochrome architecture and evolution
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DOI：
10.1074/jbc.m611824200
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发表时间：
2007-04-20
影响因子：
4.8
通讯作者：
Forest, Katrina T.
中科院分区：
文献类型：
--
作者：
Wagner, Jeremiah R.;Zhang, Junrui;Forest, Katrina T.
光敏色素是红光/远红光光致变色光受体，其指导细菌、真菌和植物界中的许多感光行为。它们由共价结合胆色素发色团的N-末端结构域和通常通过组氨酸激酶中继传递光信号的C-末端区域组成。使用X射线晶体学，我们最近解决了光敏色素的第一个三维结构，使用其发色团，胆绿素IX α组装的耐辐射异常球菌细菌光敏色素的发色团结合结构域。现在，通过设计结晶界面，我们已经实现了一个分辨率明显更高的模型。这种1.45埃分辨率的结构有助于识别晶体对称性配对物之间的广泛掩埋表面，该表面可能促进体内二聚化。它还揭示了胆绿素的C3（2）碳与Cys（24）连接后，发色团A-环在C2处呈现手性中心，从而成为2（R），3（E）-光敏色素，这是一种比以前认识到的更类似于蓝细菌和植物光敏色素的连接发色团的化学性质。细菌光敏色素进化到蓝藻和高等植物中发现的那些光敏色素必须涉及使用更多还原的胆色素（如藻蓝胆素）的更大的适应性，结合从N末端附近的半胱氨酸到cGMP磷酸二酯酶/腺苷酸环化酶/FhlA结构域内保守的半胱氨酸的连接位点的开关。通过对D. radiodurans光敏色素，我们表明，这种胆色素的偏好是部分驱动的结合位点的变化，这最终可能有助于光合生物优化阴影检测。总的来说，这些三维结构结果更好地阐明了胆色素/蛋白质的相互作用，并有助于解释高等植物光敏色素如何从原核祖细胞进化而来。
Phytochromes are red/far red light photochromic photoreceptors that direct many photosensory behaviors in the bacterial, fungal, and plant kingdoms. They consist of an N-terminal domain that covalently binds a bilin chromophore and a C-terminal region that transmits the light signal, often through a histidine kinase relay. Using x-ray crystallography, we recently solved the first three-dimensional structure of a phytochrome, using the chromophore-binding domain of Deinococcus radiodurans bacterial phytochrome assembled with its chromophore, biliverdin IX alpha. Now, by engineering the crystallization interface, we have achieved a significantly higher resolution model. This 1.45 angstrom resolution structure helps identify an extensive buried surface between crystal symmetry mates that may promote dimerization in vivo. It also reveals that upon ligation of the C3(2) carbon of biliverdin to Cys(24), the chromophore A-ring assumes a chiral center at C2, thus becoming 2(R),3(E)-phytochromobilin, a chemistry more similar to that proposed for the attached chromophores of cyanobacterial and plant phytochromes than previously appreciated. The evolution of bacterial phytochromes to those found in cyanobacteria and higher plants must have involved greater fitness using more reduced bilins, such as phycocyanobilin, combined with a switch of the attachment site from a cysteine near the N terminus to one conserved within the cGMP phosphodiesterase/adenyl cyclase/FhlA domain. From analysis of site-directed mutants in the D. radiodurans phytochrome, we show that this bilin preference was partially driven by the change in binding site, which ultimately may have helped photosynthetic organisms optimize shade detection. Collectively, these three-dimensional structural results better clarify bilin/protein interactions and help explain how higher plant phytochromes evolved from prokaryotic progenitors.