Phycobilisomes (PBS) are the major light-harvesting machineries for photosynthesis in cyanobacteria and red algae and they have a hierarchical structure of a core and peripheral rods, with both consisting of phycobiliproteins and linker proteins. Here we report the cryo-EM structures of PBS from two cyanobacterial species, Anabaena 7120 and Synechococcus 7002. Both PBS are hemidiscoidal in shape and share a common triangular core structure. While the Anabaena PBS has two additional hexamers in the core linked by the 4th linker domain of ApcE (L_CM). The PBS structures predict that, compared with the PBS from red algae, the cyanobacterial PBS could have more direct routes for energy transfer to ApcD. Structure-based systematic mutagenesis analysis of the chromophore environment of ApcD and ApcF subunits reveals that aromatic residues are critical to excitation energy transfer (EET). The structures also suggest that the linker protein could actively participate in the process of EET in both rods and the cores. These results provide insights into the organization of chromophores and the mechanisms of EET within cyanobacterial PBS.

藻胆体 (PBS) 是蓝藻和红藻光合作用的主要光捕获机制，它们具有核心和外围杆的层次结构，两者均由藻胆蛋白和连接蛋白组成。在这里，我们报告了来自两种蓝藻物种鱼腥藻71​​20和聚球藻7002 的 PBS 的低温电子显微镜结构。两种 PBS 都是半盘形的，并且共享一个共同的三角形核心结构。虽然鱼腥藻PBS 在核心中有两个额外的六聚体，由 ApcE 的第 4 个链接器域（L _CM). PBS 结构预测，与来自红藻的 PBS 相比，蓝藻 PBS 可能有更直接的途径将能量转移到 ApcD。对 ApcD 和 ApcF 亚基的发色团环境进行的基于结构的系统诱变分析表明，芳香族残基对激发能量转移 (EET) 至关重要。这些结构还表明连接蛋白可以积极参与杆状和核心中的 EET 过程。这些结果提供了对发色团组织和蓝藻 PBS 中 EET 机制的深入了解。