Liu Haijun, Zhang Hao, King Jeremy D, Wolf Nathan R, Prado Mindy, Gross Michael L, Blankenship Robert E
Department of Biology, Washington University in St. Louis, MO 63130, USA; Department of Chemistry, Washington University in St. Louis, MO 63130, USA; Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA.
Department of Chemistry, Washington University in St. Louis, MO 63130, USA; Photosynthetic Antenna Research Center (PARC), Washington University in St. Louis, MO 63130, USA.
Biochim Biophys Acta. 2014 Dec;1837(12):1955-1963. doi: 10.1016/j.bbabio.2014.09.004.
The orange carotenoid protein (OCP), a member of the family of blue light photoactive proteins, is required for efficient photoprotection in many cyanobacteria. Photoexcitation of the carotenoid in the OCP results in structural changes within the chromophore and the protein to give an active red form of OCP that is required for phycobilisome binding and consequent fluorescence quenching. We characterized the light-dependent structural changes by mass spectrometry-based carboxyl footprinting and found that an α helix in the N-terminal extension of OCP plays a key role in this photoactivation process. Although this helix is located on and associates with the outside of the β-sheet core in the C-terminal domain of OCP in the dark, photoinduced changes in the domain structure disrupt this interaction. We propose that this mechanism couples light-dependent carotenoid conformational changes to global protein conformational dynamics in favor of functional phycobilisome binding, and is an essential part of the OCP photocycle.
橙色类胡萝卜素蛋白（OCP）是蓝光光活性蛋白家族的一员，是许多蓝细菌有效光保护所必需的。OCP中类胡萝卜素的光激发导致发色团和蛋白质内部发生结构变化，产生一种活性红色形式的OCP，这是藻胆体结合及随后荧光猝灭所必需的。我们通过基于质谱的羧基足迹法表征了光依赖的结构变化，发现OCP N端延伸区的一个α螺旋在这一光激活过程中起关键作用。尽管在黑暗中这个螺旋位于OCP C端结构域β折叠核心的外部并与之结合，但该结构域结构的光诱导变化会破坏这种相互作用。我们提出，这种机制将光依赖的类胡萝卜素构象变化与整体蛋白质构象动力学联系起来，有利于功能性藻胆体结合，并且是OCP光循环的一个重要组成部分。
