The structure of the stress induced photosystem I IsiA antenna supercomplex

Photosynthetic organisms, like plants, algae and cyanobacteria populate different habitats and their adaptation to different environments is crucial for their survival. The expression of antennae and the regulation on their interaction with photosystems is critical for adaptation to different stress conditions. In low iron environments, cyanobacteria express IsiA, an antenna protein that interacts with Photosystem I and form different assemblies. We solved the structure of the PSI-IsiA single ring, a 2-MDa PSI–antenna super-complex, to 3.5 Å resolution using Cryo-EM. This is the first structure of a photosynthetic super-complex from cyanobacteria, the group where oxygenic photosynthesis evolved in. The structure reveals more than 700 pigments coordinated by 51 subunits as well the mechanisms allowing IsiA to self-assemble and associate with multiple PSI assemblies.