Abstract
Unraveling the oligomeric states of the photosystem I complex is essential to understanding the evolution and native mechanisms of photosynthesis. The molecular composition and functions of this complex are highly conserved among cyanobacteria, algae, and plants; however, its structure varies considerably between species. In cyanobacteria, the photosystem I complex is a trimer in most species, but monomer, dimer and tetramer arrangements with full physiological function have recently been characterized. Higher order oligomers have also been identified in some heterocyst-forming cyanobacteria and their close unicellular relatives. Given technological progress in cryo-electron microscope single particle technology, structures of PSI dimers, tetramers and some heterogeneous supercomplexes have been resolved into near atomic resolution. Recent developments in photosystem I oligomer studies have largely enriched theories on the structure and function of these photosystems.
Highlights
Photosystem I (PSI) is a light-driven membrane protein complex that transfers electrons from plastocyanin/cytochrome C to ferredoxin/flavodoxin in oxygenic photosynthetic organisms (Amunts and Nelson, 2009)
An understanding of homogenous and heterogenous PSI supercomplexes is required to understand the native mechanisms of photosynthesis
Monomeric PSI exhibits a complete range of physiological functions in cyanobacteria compared with the previously-established range for the trimer
Summary
Photosystem I (PSI) is a light-driven membrane protein complex that transfers electrons from plastocyanin/cytochrome C to ferredoxin/flavodoxin in oxygenic photosynthetic organisms (Amunts and Nelson, 2009). Twelve subunits have been identified in cyanobacteria, nine of which (PsaA, PsaB, PsaF, PsaJ, PsaI, PsaK, PsaL, PsaM, and PsaX) are transmembrane proteins, and three of which (PsaC, PsaD and PsaE) are membrane extrinsic proteins, located on the stromal side of the PSI complex (Jordan et al, 2001).
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