Ma Jianfei, You Xin, Sun Shan, Sui Sen-Fang
State Key Laboratory of Membrane Biology, Beijing Frontier Research Center for Biological Structures, School of Life Sciences, Tsinghua University, Beijing, China.
State Key Laboratory of Medicinal Chemical Biology and College of Life Sciences, Nankai University, Tianjin, China.
Nat Commun. 2025 Jul 1;16(1):5956. doi: 10.1038/s41467-025-60673-w.
Gloeobacter diverged from other lineages early in cyanobacterial evolution, preferentially growing under low light intensity conditions. Among cyanobacteria, G. violaceus exhibits unique features, including lack of a thylakoid membrane and bundle-shaped antenna phycobilisomes (PBSs), densely packed and well-organized on the plasma membrane. However, without high-resolution structures, it has remained unclear how G. violaceus PBSs assemble into a bundle-shaped configuration. Here we solve the cryo-EM structures of PBSs from G. violaceus cells cultured under low (Sr-PBS) or moderate (Lr-PBS) light intensity. These structures reveal two unique linker proteins, L and L, that play a key role in the PBS architecture. Analysis of the bilin arrangement indicates that the bundle-shaped structure allows efficient energy transfer among rods. Moreover, comparison between Lr-PBS and Sr-PBS uncovers a distinct mode of adaption to increased light intensity wherein the ApcA-ApcB-ApcD layer can be blocked from binding to the core by altering structural elements exclusively found in the G. violaceus L. This study illustrates previously unrecognized mechanisms of assembly and adaptation to varying light intensity in the bundle-shaped PBS of G. violaceus.
蓝杆菌在蓝藻进化早期就与其他谱系分化，偏好于在低光照强度条件下生长。在蓝藻中，紫球藻表现出独特的特征，包括缺乏类囊体膜以及在质膜上密集堆积且排列有序的束状天线藻胆体（PBS）。然而，由于缺乏高分辨率结构，紫球藻PBS如何组装成束状结构仍不清楚。在此，我们解析了在低光（Sr-PBS）或中等光（Lr-PBS）强度下培养的紫球藻细胞中PBS的冷冻电镜结构。这些结构揭示了两种独特的连接蛋白L和L，它们在PBS结构中起关键作用。对藻胆素排列的分析表明，束状结构允许棒状体之间进行高效的能量转移。此外，Lr-PBS和Sr-PBS之间的比较揭示了一种适应光照强度增加的独特模式，其中ApcA-ApcB-ApcD层可以通过改变紫球藻L中特有的结构元件而被阻止与核心结合。本研究阐明了紫球藻束状PBS中以前未被认识到的组装机制以及对不同光照强度的适应性。
