Yang Xiaojing, Stojković Emina A, Ozarowski Wesley B, Kuk Jane, Davydova Erna, Moffat Keith
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA; Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA; Department of Ophthalmology and Vision Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA.
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA; Department of Biology, Northeastern Illinois University, Chicago, IL 60625, USA.
Structure. 2015 Jul 7;23(7):1179-89. doi: 10.1016/j.str.2015.04.022. Epub 2015 Jun 18.
RpBphP2 and RpBphP3, two tandem bacteriophytochromes from the photosynthetic bacterium Rhodopseudomonas palustris, share high sequence identity but exhibit distinct photoconversion behavior. Unlike the canonical RpBphP2, RpBphP3 photoconverts to an unusual near-red-absorbing (Pnr) state; both are required for synthesis of light-harvesting complexes under low-light conditions. Here we report the crystal structures of the photosensory core modules of RpBphP2 and RpBphP3. Despite different quaternary structures, RpBphP2 and RpBphP3 adopt nearly identical tertiary structures. The RpBphP3 structure reveals tongue-and-groove interactions at the interface between the GAF and PHY domains. A single mutation in the PRxSF motif at the GAF-PHY interface abolishes light-induced formation of the Pnr state in RpBphP3, possibly due to altered structural rigidity of the chromophore-binding pocket. Structural comparisons suggest that long-range signaling involves structural rearrangement of the helical spine at the dimer interface. These structures, together with mutational studies, provide insights into photoconversion and the long-range signaling mechanism in phytochromes.
RpBphP2和RpBphP3是来自光合细菌沼泽红假单胞菌的两个串联细菌光敏色素，它们具有高度的序列同一性，但表现出不同的光转化行为。与典型的RpBphP2不同，RpBphP3光转化为一种不寻常的近红外吸收（Pnr）状态；在低光条件下，两者都是合成光捕获复合物所必需的。在这里，我们报告了RpBphP2和RpBphP3的光感核心模块的晶体结构。尽管四级结构不同，但RpBphP2和RpBphP3采用了几乎相同的三级结构。RpBphP3的结构揭示了GAF和PHY结构域之间界面处的榫槽相互作用。GAF-PHY界面处PRxSF基序中的单个突变消除了RpBphP3中光诱导的Pnr状态的形成，这可能是由于生色团结合口袋的结构刚性改变所致。结构比较表明，长程信号传导涉及二聚体界面处螺旋脊柱的结构重排。这些结构以及突变研究，为光敏色素的光转化和长程信号传导机制提供了见解。
