Abstract
In plants, algae, and cyanobacteria, photosystem II (PSII) catalyzes the oxidation of water into molecular oxygen at a Mn4CaO5 cluster. The largest extrinsic subunit of PSII, PsbO, is required for efficient oxygen evolution. PsbO maintains the normal function of the oxygen evolution cluster (OEC). Removal of PsbO leads to loss of oxygen evolution activity, and reconstitution restores activity (1). PsbO has been proposed to be involved in proton transfer through a hydrogen‐bonding network that extends from the metal cluster to the lumen (2). PsbO is observed to form a beta barrel with long loop regions, when bound either to the cyanobacterial (3) or plant PSII reaction center (4). However, the solution structure of intact PsbO, containing all potentially flexible loop regions, is not yet known (5). When released from the PSII, either by urea treatment or calcium chloride washing, or when produced recombinantly, PsbO exhibits a low pI, an exaggerated size estimate on SDS‐PAGE and gel filtration, thermostability, and a high content of disordered structure. Other characteristics of intrinsically disordered regions are also observed in PsbO, including low sequence complexity and enrichment in polar and charged residues. In addition, recombinant, calcium‐released, and urea‐released PsbO all exhibit different amide I infrared line shapes (6, 7), although all these preparations reconstitute activity in PSII. Here, we test the hypothesis that PsbO is an intrinsically disordered subunit and that its disordered, flexible nature promotes photosynthetic water oxidation. Recent progress will be discussed.Support or Funding InformationNSF MCB 14‐11734This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
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