PDF(Pubmed)
Abstract：
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 (LCM). 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.
摘要：
藻胆体（PBS）是蓝细菌和红藻光合作用的主要捕光装置，它们具有核心和外围杆的层次结构，两者都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细菌物种的PBS的低温EM结构，鱼腥草7120和复合球菌7002。两种PBS的形状均为半盘状，并具有共同的三角形核心结构。而鱼腥草PBS在核心中具有通过ApcE(LCM)的第4个接头结构域连接的两个额外的六聚体。PBS结构预测，与来自红藻的PBS相比，蓝细菌PBS可以有更直接的能量转移到ApcD的途径。ApcD和ApcF亚基的发色团环境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。该结构还表明，接头蛋白可以在杆和核心中积极参与EET的过程。这些结果为蓝细菌PBS中发色团的组织和EET的机制提供了见解。
