title: Engineered Photosystem II reaction centers optimize photochemistry versus photoprotection at different solar intensities.
abstract: The D1 protein of Photosystem II (PSII) provides most of the ligating amino acid residues for the Mn4CaO5 water-oxidizing complex (WOC) and half of the reaction center cofactors, and it is present as two isoforms in the cyanobacterium Synechococcus elongatus PCC 7942. These isoforms, D1:1 and D1:2, confer functional advantages for photosynthetic growth at low and high light intensities, respectively. D1:1, D1:2, and seven point mutations in the D1:2 background that are native to D1:1 were expressed in the green alga Chlamydomonas reinhardtii. We used these nine strains to show that those strains that confer a higher yield of PSII charge separation under light-limiting conditions (where charge recombination is significant) have less efficient photochemical turnover, measured in terms of both a lower WOC turnover probability and a longer WOC cycle period. Conversely, these same strains under light saturation (where charge recombination does not compete) confer a correspondingly faster O2 evolution rate and greater protection against photoinhibition. Taken together, the data clearly establish that PSII primary charge separation is a trade-off between photochemical productivity (water oxidation and plastoquinone reduction) and charge recombination (photoprotection). These trade-offs add up to a significant growth advantage for the two natural isoforms. These insights provide fundamental design principles for engineering of PSII reaction centers with optimal photochemical efficiencies for growth at low versus high light intensities.
authors.affiliation: Department of Chemistry and Chemical Biology and ‡Waksman Institute of Microbiology, Rutgers, The State University of New Jersey , Piscataway, New Jersey 08854, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Vinyard
authors.forename: Javier
authors.initials: J
authors.lastname: Gimpel
authors.forename: Gennady M
authors.initials: GM
authors.lastname: Ananyev
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Mayfield
authors.forename: G Charles
authors.initials: GC
authors.lastname: Dismukes
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D008027:Light; D010100:Oxygen / Q000378:metabolism; D010777:Photochemistry; D045332:Photosystem II Protein Complex / Q000235:genetics* / Q000378:metabolism; D017354:Point Mutation; D015202:Protein Engineering; D046940:Synechococcus / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D010100:Oxygen