Allophycocyanin A is a carbon dioxide receptor in the cyanobacterial phycobilisome
Alejandra Guillén-García, Savannah E. R. Gibson, Caleb J. C. Jordan, Venkata K. Ramaswamy, Victoria L. Linthwaite, Elizabeth H. C. Bromley, Adrian P. Brown, David R. W. Hodgson, Tim R. Blower, Jan R. R. Verlet, Matteo T. Degiacomi, Lars-Olof Pålsson & Martin J. Cann
Light harvesting is fundamental for production of ATP and reducing equivalents for CO2 fixation during photosynthesis. However, electronic energy transfer (EET) through a photosystem can harm the photosynthetic apparatus when not balanced with CO2. Here, we show that CO2 binding to the light-harvesting complex modulates EET in photosynthetic cyanobacteria. More specifically, CO2 binding to the allophycocyanin alpha subunit of the light-harvesting complex regulates EET and its fluorescence quantum yield in the cyanobacterium Synechocystis sp. PCC 6803. CO2 binding decreases the inter-chromophore distance in the allophycocyanin trimer. The result is enhanced EET in vitro and in live cells. Our work identifies a direct target for CO2 in the cyanobacterial light-harvesting apparatus and provides insights into photosynthesis regulation.
ATP, EET, cells, photosynthesis regulation