title: Functional asymmetry of photosystem II D1 and D2 peripheral chlorophyll mutants of Chlamydomonas reinhardtii.
abstract: The peripheral accessory chlorophylls (Chls) of the photosystem II (PSII) reaction center (RC) are coordinated by a pair of symmetry-related histidine residues (D1-H118 and D2-H117). These Chls participate in energy transfer from the proximal antennae complexes (CP43 and CP47) to the RC core chromophores. In addition, one or both of the peripheral Chls are redox-active and participate in a low-quantum-yield electron transfer cycle around PSII. We demonstrate that conservative mutations of the D2-H117 residue result in decreased Chl fluorescence quenching efficiency attributed to reduced accumulation of the peripheral accessory Chl cation, Chl(Z)(+). In contrast, identical symmetry-related mutations at residue D1-H118 had no effect on Chl fluorescence yield or quenching kinetics. Mutagenesis of the D2-H117 residue also altered the line width of the Chl(Z)(+) EPR signal, but the line shape of the D1-H118Q mutant remained unchanged. The D1-H118 and D2-H117 mutations also altered energy transfer properties in PSII RCs. Unlike wild type or the D1-H118Q mutant, D2-H117N RCs exhibited a reduced CD doublet in the red region of Chl absorbance band, indicative of reduced energetic coupling between P680 and the peripheral accessory Chl. In addition, transient absorption measurements of D2-H117N RCs, excited on the blue side of the Chl absorbance band, exhibited a ( approximately 400 fs) pheophytin Q(X) band bleach lifetime component not seen in wild-type or D1-H118Q RCs. The origin of this component may be related to delayed fast-energy equilibration of the excited state between the core pigments of this mutant.
authors.affiliation: Department of Plant Biology, Ohio State University, Columbus, OH 43210, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.forename: David
authors.initials: D
authors.lastname: Gosztola
authors.forename: Stuart V
authors.initials: SV
authors.lastname: Ruffle
authors.forename: Craig
authors.initials: C
authors.lastname: Hemann
authors.forename: Michael
authors.initials: M
authors.lastname: Seibert
authors.forename: Michael R
authors.initials: MR
authors.lastname: Wasielewski
authors.forename: Russ
authors.initials: R
authors.lastname: Hille
authors.forename: Terry L
authors.initials: TL
authors.lastname: Gustafson
authors.forename: Richard T
authors.initials: RT
authors.lastname: Sayre
mesh_terms: D000042:Absorption; D000818:Animals; D002412:Cations / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000166:cytology / Q000235:genetics* / Q000378:metabolism*; D002734:Chlorophyll / Q000235:genetics* / Q000378:metabolism*; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D004735:Energy Transfer; D005453:Fluorescence; D009154:Mutation / Q000235:genetics*; D010084:Oxidation-Reduction; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism
chemical_list: D002412:Cations; D015800:Protozoan Proteins; D002734:Chlorophyll