Wahadoszamen Md, Belgio Erica, Rahman Md Ashiqur, Ara Anjue Mane, Ruban Alexander V, van Grondelle Rienk
Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, The Netherlands; Department of Physics, University of Dhaka, Dhaka 1000, Bangladesh.
Institute of Microbiology, Academy of Sciences of the Czech Republic, Opatovický mlýn, 379 81 Třeboň, Czech Republic; School of Biological and Chemical Sciences, Department of Cell and Molecular Biology, Queen Mary University of London.
Biochim Biophys Acta. 2016 Dec;1857(12):1917-1924. doi: 10.1016/j.bbabio.2016.09.010. Epub 2016 Sep 23.
Aggregation induced conformational change of light harvesting antenna complexes is believed to constitute one of the pathways through which photosynthetic organisms can safely dissipate the surplus of energy while exposed to saturating light. In this study, Stark fluorescence (SF) spectroscopy is applied to minor antenna complexes (CP24, CP26 and CP29) both in their light-harvesting and energy-dissipating states to trace and characterize different species generated upon energy dissipation through aggregation (in-vitro) induced conformational change. SF spectroscopy could identify three spectral species in the dissipative state of CP24, two in CP26 and only one in CP29. The comprehensive analysis of the SF spectra yielded different sets of molecular parameters for the multiple spectral species identified in CP24 or CP26, indicating the involvement of different pigments in their formation. Interestingly, a species giving emission around the 730nm spectral region is found to form in both CP24 and CP26 following transition to the energy dissipative state, but not in CP29. The SF analyses revealed that the far red species has exceptionally large charge transfer (CT) character in the excited state. Moreover, the far red species was found to be formed invariably in both Zeaxanthin (Z)- and Violaxathin (V)-enriched CP24 and CP26 antennas with identical CT character but with larger emission yield in Z-enriched ones. This suggests that the carotenoid Z is not directly involved but only confers an allosteric effect on the formation of the far red species. Similar far red species with remarkably large CT character were also observed in the dissipative state of the major light harvesting antenna (LHCII) of plants [Wahadoszamen et al. PCCP, 2012], the fucoxanthin-chlorophyll protein (FCP) of brown algae [Wahadoszamen et al. BBA, 2014] and cyanobacterial IsiA [Wahadoszamen et al. BBA, 2015], thus pointing to identical sites and pigments active in the formation of the far red quenching species in different organisms.
聚光天线复合物的聚集诱导构象变化被认为是光合生物在暴露于饱和光时安全耗散多余能量的途径之一。在本研究中,将斯塔克荧光(SF)光谱应用于次要天线复合物(CP24、CP26和CP29)处于光捕获和能量耗散状态时,以追踪和表征通过聚集(体外)诱导构象变化在能量耗散过程中产生的不同物种。SF光谱可以在CP24的耗散状态中识别出三种光谱物种,在CP26中识别出两种,在CP29中仅识别出一种。对SF光谱的综合分析为在CP24或CP26中识别出的多个光谱物种产生了不同的分子参数集,表明不同色素参与了它们的形成。有趣的是,在CP24和CP26转变到能量耗散状态后,在730nm光谱区域附近发射的一个物种都能形成,但在CP29中则不然。SF分析表明,远红物种在激发态具有异常大的电荷转移(CT)特性。此外,发现远红物种在富含玉米黄质(Z)和紫黄质(V)的CP24和CP26天线中总是以相同的CT特性形成,但在富含Z的天线中发射产率更高。这表明类胡萝卜素Z不直接参与,但仅对远红物种的形成赋予变构效应。在植物的主要光捕获天线(LHCII)[Wahadoszamen等人,PCCP,2012]、褐藻的岩藻黄素 - 叶绿素蛋白(FCP)[Wahadoszamen等人,BBA,2014]和蓝藻的IsiA[Wahadoszamen等人,BBA,2015]的耗散状态中也观察到具有显著大CT特性的类似远红物种,因此表明在不同生物体中远红猝灭物种形成中相同的位点和色素是活跃的。