title: Photosystem II peripheral accessory chlorophyll mutants in Chlamydomonas reinhardtii. Biochemical characterization and sensitivity to photo-inhibition.
abstract: In addition to the four chlorophylls (Chls) involved in primary charge separation, the photosystem II (PSII) reaction center polypeptides, D1 and D2, coordinate a pair of symmetry-related, peripheral accessory Chls. These Chls are axially coordinated by the D1-H118 and D2-H117 residues and are in close association with the proximal Chl antennae proteins, CP43 and CP47. To gain insight into the function(s) of each of the peripheral Chls, we generated site-specific mutations of the amino acid residues that coordinate these Chls and characterized their energy and electron transfer properties. Our results demonstrate that D1-H118 and D2-H117 mutants differ with respect to: (a) their relative numbers of functional PSII complexes, (b) their relative ability to stabilize charge-separated states, (c) light-harvesting efficiency, and (d) their sensitivity to photo-inhibition. The D2-H117N and D2-H117Q mutants had reduced levels of functional PSII complexes and oxygen evolution capacity as well as reduced light-harvesting efficiencies relative to wild-type cells. In contrast, the D1-H118Q mutant was capable of near wild-type rates of oxygen evolution at saturating light intensities. The D1-H118Q mutant also was substantially more resistant to photo-inhibition than wild type. This reduced sensitivity to photo-inhibition is presumably associated with a reduced light-harvesting efficiency in this mutant. Finally, it is noted that the PSII peripheral accessory Chls have similarities to a to a pair of Chls also present in the PSI reaction center complex.
authors.affiliation: School of Biological Sciences, University of Exeter, Exeter EX4 4PS, United Kingdom.
authors.forename: S V
authors.initials: SV
authors.lastname: Ruffle
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: H G
authors.initials: HG
authors.lastname: Johnston
authors.forename: T L
authors.initials: TL
authors.lastname: Gustafson
authors.forename: R S
authors.initials: RS
authors.lastname: Hutchison
authors.forename: J
authors.initials: J
authors.lastname: Minagawa
authors.forename: A
authors.initials: A
authors.lastname: Crofts
authors.forename: R T
authors.initials: RT
authors.lastname: Sayre
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000235:genetics / Q000378:metabolism*; D003624:Darkness; D004237:Diuron / Q000494:pharmacology; D004579:Electron Transport; D006540:Herbicides / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008345:Manganese / Q000032:analysis; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D020524:Thylakoids / Q000235:genetics / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D006540:Herbicides; D008024:Ligands; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; D002734:Chlorophyll; D008345:Manganese; D004237:Diuron; D010100:Oxygen