The structure of a plant photosystem I supercomplex at 3.4 Å resolution

All higher organisms on Earth receive energy directly or indirectly from oxygenic photosynthesis performed by plants, green algae and cyanobacteria. Photosystem I (PSI) is a supercomplex of a reaction centre and light-harvesting complexes. It generates the most negative redox potential in nature, and thus largely determines the global amount of enthalpy in living systems. We report the structure of plant PSI at 3.4 Å resolution, revealing 17 protein subunits. PsaN was identified in the luminal side of the supercomplex, and most of the amino acids in the reaction centre were traced. The crystal structure of PSI provides a picture at near atomic detail of 11 out of 12 protein subunits of the reaction centre. At this level, 168 chlorophylls (65 assigned with orientations for Qx and Qy transition dipole moments), 2 phylloquinones, 3 Fe4S4 clusters and 5 carotenoids are described. This structural information extends the understanding of the most efficient nano-photochemical machine in nature. Oxygenic photosynthesis occurs in plants, green algae and cyanobacteria and directly or indirectly provides energy for all higher organisms on Earth. Photosystem I (PSI) — a protein supercomplex that contains a reaction centre and light-harvesting complexes — is involved in this process, and is a star performer in energy gathering terms: it is the most efficient photochemical machine in nature, with almost every photon absorbed by the PSI complex being used to drive electron transport. The X-ray crystal structure of plant PSI has now been determined to 3.4 Å resolution, revealing 17 protein subunits, 168 chlorophylls, two phylloquinones, three Fe4S4 clusters and five carotenoids. The X-ray crystal structure of plant photosystem I is solved to 3.4 Å resolution, revealing 17 protein subunits. This structure provides a picture of 11 out of 12 protein subunits of the reaction centre, 168 chlorophylls, two phylloquinones, three Fe4S4 clusters, and five carotenoids.