Faculty of Biology, Institute of Biology III, University of Freiburg, 79104, Freiburg, Germany.
Department of Life Sciences (Biology), Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro, Tokyo, 153-8902, Japan.
Photochem Photobiol Sci. 2023 Jul;22(7):1561-1572. doi: 10.1007/s43630-023-00397-2. Epub 2023 Mar 1.
The phycobilisome (PBS) is an antenna protein complex in cyanobacteria, Glaucocystophytes, and red algae. In the standard PBS, the rod-core PBS, the rods are connected to the core by the rod-core linker protein CpcG. The rod-core PBS transfers the light energy mainly to photosystem (PS) II and to a lesser extent to PSI. Cyanobacteria assemble another type of PBS, the CpcL-PBS, which consists of only one rod. This rod-type PBS is connected to the thylakoid membrane by the linker protein CpcL and is a PSI-specific antenna. In the filamentous heterocyst-forming cyanobacterium Anabaena (Nostoc) sp. PCC 7120, the CpcL-PBS forms a complex with the tetrameric PSI (PBS-PSI supercomplex). The CpcL-PBS and the rod part of the rod-core PBS are identical except for the linker proteins CpcL and CpcG. How cells control the accumulation of the two different types of PBS is unknown. Here, we analyzed two mutant strains which either lack the major rod-core linker CpcG4 or overexpress the rod-membrane linker CpcL. In both mutant strains, more and larger PBS-PSI supercomplexes accumulated compared to the wild type. Our results suggest that CpcL and CpcG4 compete for the same phycobiliprotein pool, and therefore the CpcL/CpcG4 ratio determines the levels of PBS-PSI supercomplexes. We propose that the CpcL-PBS and the rod-core PBS fulfill distinct functions in light harvesting.
藻胆体（PBS）是蓝细菌、蓝藻和红藻中的一种天线蛋白复合物。在标准 PBS 中，棒-核心 PBS 的棒通过棒-核心连接蛋白 CpcG 与核心相连。棒-核心 PBS 将光能主要传递给光系统 II（PSII），并在较小程度上传递给 PSI。蓝细菌组装另一种 PBS，即 CpcL-PBS，它只由一个棒组成。这种棒型 PBS 通过连接蛋白 CpcL 与类囊体膜相连，是 PSI 特有的天线。在丝状异形胞形成蓝细菌鱼腥藻（念珠藻）属 PCC 7120 中，CpcL-PBS 与四聚体 PSI（PBS-PSI 超复合物）形成复合物。CpcL-PBS 和棒-核心 PBS 的棒部分除了连接蛋白 CpcL 和 CpcG 外是相同的。细胞如何控制两种不同类型 PBS 的积累尚不清楚。在这里，我们分析了两种突变株，它们要么缺乏主要的棒-核心连接蛋白 CpcG4，要么过表达棒-膜连接蛋白 CpcL。在这两种突变株中，与野生型相比，更多和更大的 PBS-PSI 超复合物积累。我们的结果表明，CpcL 和 CpcG4 竞争相同的藻胆蛋白库，因此 CpcL/CpcG4 比值决定了 PBS-PSI 超复合物的水平。我们提出，CpcL-PBS 和棒-核心 PBS 在光捕获中发挥不同的功能。
