Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands.
Department of Biological Sciences, Biochemistry and Molecular Biology Section, Louisiana State University, Baton Rouge, LA 70803, United States.
Biochim Biophys Acta Bioenerg. 2017 May;1858(5):371-378. doi: 10.1016/j.bbabio.2017.02.012. Epub 2017 Feb 22.
Photosystems I and II (PSI and PSII) work in series to drive oxygenic photosynthesis. The two photosystems have different absorption spectra, therefore changes in light quality can lead to imbalanced excitation of the photosystems and a loss in photosynthetic efficiency. In a short-term adaptation response termed state transitions, excitation energy is directed to the light-limited photosystem. In higher plants a special pool of LHCII antennae, which can be associated with either PSI or PSII, participates in these state transitions. It is known that one LHCII antenna can associate with the PsaH site of PSI. However, membrane fractions were recently isolated in which multiple LHCII antennae appear to transfer energy to PSI. We have used time-resolved fluorescence-streak camera measurements to investigate the energy transfer rates and efficiency in these membrane fractions. Our data show that energy transfer from LHCII to PSI is relatively slow. Nevertheless, the trapping efficiency in supercomplexes of PSI with ~2.4 LHCIIs attached is 94%. The absorption cross section of PSI can thus be increased with ~65% without having significant loss in quantum efficiency. Comparison of the fluorescence dynamics of PSI-LHCII complexes, isolated in a detergent or located in their native membrane environment, indicates that the environment influences the excitation energy transfer rates in these complexes. This demonstrates the importance of studying membrane protein complexes in their natural environment.
光系统 I 和 II（PSI 和 PSII）串联工作以驱动放氧光合作用。这两个光系统具有不同的吸收光谱，因此光质的变化会导致光系统的激发不平衡，并导致光合作用效率的损失。在一种称为状态转变的短期适应反应中，激发能被引导到光限制的光系统。在高等植物中，一种特殊的 LHCII 天线池可以与 PSI 或 PSII 相关联，参与这些状态转变。已知一个 LHCII 天线可以与 PSI 的 PsaH 位点结合。然而，最近分离出的膜部分表明，多个 LHCII 天线似乎可以将能量转移到 PSI。我们使用时间分辨荧光条纹相机测量来研究这些膜部分中的能量转移速率和效率。我们的数据表明，从 LHCII 到 PSI 的能量转移相对较慢。尽管如此，附着有2.4 个 LHCII 的 PSI 超复合物的捕集效率为 94%。因此，PSI 的吸收截面可以增加65%，而量子效率没有明显损失。PSI-LHCII 复合物的荧光动力学比较，无论是在去污剂中分离还是位于其天然膜环境中，都表明环境会影响这些复合物中的激发能量转移速率。这证明了在其自然环境中研究膜蛋白复合物的重要性。
