The D-ring, Not the A-ring, Rotates in Synechococcus OS-B′ Phytochrome*
The D-ring, Not the A-ring, Rotates in Synechococcus OS-B′ Phytochrome*
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聚球藻 OS-B′ 光敏色素中旋转的是 D 环，而不是 A 环*
DOI：
10.1074/jbc.m113.520031
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
F. Siebert
中科院分区：
文献类型：
--
作者：
H. Foerstendorf;T. Lamparter;J. Hughes;W. Gärtner;F. Siebert
背景：光敏色素光感受器通过光诱导的发色团辅因子异构化而被激活。结果如下：聚球藻OS-B′光敏色素的光活化破坏了一个不寻常的发色团D-环氢键，而只有微妙的变化发生在A-环连接到蛋白质。结论：激活来自于强倾斜D环的光翻转。意义：A环在光子吸收后旋转的假设是错误的。植物和微生物中的光敏色素光感受器在两种状态之间切换光致变色，控制许多重要的生物过程。尽管这种光转化通常被认为涉及四吡咯发色团的D环的旋转，但Ulijasz等人（Ulijasz，A. T.，Cornilescu，G.，科尔尼列斯库角C.的方法，张杰，里维拉，M.，Markley，J.L.，和Vierstra，R. D.（2010）Nature 463，250-254）提出A环代替地旋转。在这里，我们应用魔角旋转NMR的两个母态以下的23-kDa的GAF（cGMP磷酸二酯酶/腺苷酸环化酶/FhlA）结构域片段的研究从聚球藻OS-B′光敏色素。主要变化发生在A环与蛋白质的共价键以及D环的蛋白质残基接触处。与A环氮相关的保守接触排除了A环光翻转，而D环氮与蛋白质接触的丧失意味着D环的移动。虽然没有一个次甲基桥显示出与典型光敏色素中D环光翻转特征相当的化学位移变化，但变性实验最终表明，聚球藻OS-B′光敏色素在光转化时也发生了同样的变化。结果与D-环在两种状态下强烈倾斜和C15=C16双键在光吸收时经历Z/E异构化一致。更微妙的变化与蛋白质的A环连接有关。因此，我们的研究结果反驳了A-环旋转和讨论有关的D-环，光异构化，光敏色素家族的光致变色性的位置。
Background: Phytochrome photoreceptors are activated by light-induced isomerization of the chromophore cofactor. Results: Photoactivation of Synechococcus OS-B′ phytochrome breaks an unusual chromophore D-ring hydrogen bond, whereas only subtle changes occur at the A-ring linkage to the protein. Conclusion: Activation arises from a photoflip of a strongly tilted D-ring. Significance: The hypothesis that the A-ring rotates upon photon absorption is wrong. Phytochrome photoreceptors in plants and microorganisms switch photochromically between two states, controlling numerous important biological processes. Although this phototransformation is generally considered to involve rotation of ring D of the tetrapyrrole chromophore, Ulijasz et al. (Ulijasz, A. T., Cornilescu, G., Cornilescu, C. C., Zhang, J., Rivera, M., Markley, J. L., and Vierstra, R. D. (2010) Nature 463, 250–254) proposed that the A-ring rotates instead. Here, we apply magic angle spinning NMR to the two parent states following studies of the 23-kDa GAF (cGMP phosphodiesterase/adenylyl cyclase/FhlA) domain fragment of phytochrome from Synechococcus OS-B′. Major changes occur at the A-ring covalent linkage to the protein as well as at the protein residue contact of ring D. Conserved contacts associated with the A-ring nitrogen rule out an A-ring photoflip, whereas loss of contact of the D-ring nitrogen to the protein implies movement of ring D. Although none of the methine bridges showed a chemical shift change comparable with those characteristic of the D-ring photoflip in canonical phytochromes, denaturation experiments showed conclusively that the same occurs in Synechococcus OS-B′ phytochrome upon photoconversion. The results are consistent with the D-ring being strongly tilted in both states and the C15=C16 double bond undergoing a Z/E isomerization upon light absorption. More subtle changes are associated with the A-ring linkage to the protein. Our findings thus disprove A-ring rotation and are discussed in relation to the position of the D-ring, photoisomerization, and photochromicity in the phytochrome family.