Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA.
Biodesign Institute, School of Molecular Sciences, Arizona State University, Tempe, AZ, 85801, USA.
Nat Commun. 2023 Aug 2;14(1):4650. doi: 10.1038/s41467-023-40146-8.
Photosynthetic organisms transport and convert solar energy with near-unity quantum efficiency using large protein supercomplexes held in flexible membranes. The individual proteins position chlorophylls to tight tolerances considered critical for fast and efficient energy transfer. The variability in protein organization within the supercomplexes, and how efficiency is maintained despite variability, had been unresolved. Here, we report on structural heterogeneity in the 2-MDa cyanobacterial PSI-IsiA photosynthetic supercomplex observed using Cryo-EM, revealing large-scale variances in the positions of IsiA relative to PSI. Single-molecule measurements found efficient IsiA-to-PSI energy transfer across all conformations, along with signatures of transiently decoupled IsiA. Structure based calculations showed that rapid IsiA-to-PSI energy transfer is always maintained, and even increases by three-fold in rare conformations via IsiA-specific chls. We postulate that antennae design mitigates structural fluctuations, providing a mechanism for robust energy transfer in the flexible membrane.
光合生物利用大型蛋白质超复合体在柔性膜中进行近乎一致的量子效率的太阳能运输和转换。这些单个蛋白质将叶绿素定位到严格的容差内，这些容差被认为对快速高效的能量转移至关重要。尽管存在可变性，但超复合体中蛋白质组织的可变性以及如何维持效率仍然没有得到解决。在这里，我们使用 Cryo-EM 报告了在 2-MDa 蓝细菌 PSI-IsiA 光合作用超复合体中观察到的结构异质性，揭示了相对于 PSI 的 IsiA 位置的大规模差异。单分子测量发现，所有构象都能有效地进行 IsiA 到 PSI 的能量转移，同时还具有 IsiA 暂时解耦的特征。基于结构的计算表明，快速的 IsiA 到 PSI 的能量转移总是得到维持，并且通过 IsiA 特异性 chls 在罕见构象中增加了三倍。我们假设天线设计减轻了结构波动，为柔性膜中稳健的能量转移提供了一种机制。
