Photosynthesis Research

, 98:449

D1-arginine257 mutants (R257E, K, and Q) of Chlamydomonas reinhardtii have a lowered QB redox potential: analysis of thermoluminescence and fluorescence measurements

  • Stuart Rose
  • Jun Minagawa
  • Manfredo Seufferheld
  • Sean Padden
  • Bengt Svensson
  • Derrick R. J. Kolling
  • Antony R. Crofts
  • Govindjee
Regular Paper

DOI: 10.1007/s11120-008-9351-9

Cite this article as:
Rose, S., Minagawa, J., Seufferheld, M. et al. Photosynth Res (2008) 98: 449. doi:10.1007/s11120-008-9351-9

Abstract

Arginine257 (R257), in the de-helix that caps the QB site of the D1 protein, has been shown by mutational studies to play a key role in the sensitivity of Photosystem II (PS II) to bicarbonate-reversible binding of the formate anion. In this article, the role of this residue has been further investigated through D1 mutations (R257E, R257Q, and R257K) in Chlamydomonas reinhardtii. We have investigated the activity of the QB site by studying differences from wild type on the steady-state turnover of PS II, as assayed through chlorophyll (Chl) a fluorescence yield decay after flash excitation. The effects of p-benzoquinone (BQ, which oxidizes reduced QB, QB) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU, which blocks electron flow from QA to QB) were measured. The equilibrium constants of the two-electron gate were obtained through thermoluminescence measurements. The thermoluminescence properties were changed in the mutants, especially when observed after pretreatment with 100 μM BQ. A theoretical analysis of the thermoluminescence data, based mainly on the recombination pathways model of Rappaport et al. (2005), led to the conclusion that the free-energy difference for the recombination of QB with S2 was reduced by 20–40 mV in the three mutants (D1-R257K, D1-R257Q, and D1-R257E); this was interpreted to be due to a lowering of the redox potential of QB/QB. Further, since the recombination of QA with S2 was unaffected, we suggest that no significant change in redox potential of QA/QA occurred in these three mutants. The maximum variable Chl a fluorescence yield is lowered in the mutants, in the order R257K > R257Q > R257E, compared to wild type. Our analysis of the binary oscillations in Chl a fluorescence following pretreatment of cells with BQ showed that turnover of the QB site was relatively unaffected in the three mutants. The mutant D1-R257E had the lowest growth rate and steady-state activity and showed the weakest binary oscillations. We conclude that the size and the charge of the amino acid at the position D1-257 play a role in PS II function by modulating the effective redox potential of the QB/QB pair. We discuss an indirect mechanism mediated through electrostatic and/or surface charge effects and the possibility of more pleiotropic effects arising from decreased stability of the D1/D2 and D1/CP47 interfaces.

Keywords

D1-R257 mutants Bicarbonate in Photosystem II Thermoluminescence Theory of thermoluminescence Chlorophyll a fluorescence yield decay Electron acceptor side of Photosystem II Redox potentials of QA/QA and QB/QB Chlamydomonas reinhardtii Two-electron gate in Photosystem II Benzoquinone 

Abbreviations

BQ

p-Benzoquinone

C. reinhardtii

Chlamydomonas reinhardtii

Chl

Chlorophyll

18-Crown-6

Dicyclohexano-hexaoxacyclooctadecane

DCMU

3-(3,4-Dichlorophenyl)-1,1-dimethylurea

DMBQ

2,5-Dimethyl-p-benzoquinone

HS

High salt culture medium

ms

Millisecond(s)

PS II

Photosystem II

Ph

Pheophytin

QA

Primary plastoquinone electron acceptor of Photosystem II

QB

Secondary plastoquinone electron acceptor of Photosystem II

TAP

Tris–acetate–phosphate culture medium

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • Stuart Rose
    • 1
  • Jun Minagawa
    • 2
  • Manfredo Seufferheld
    • 3
  • Sean Padden
    • 4
  • Bengt Svensson
    • 5
  • Derrick R. J. Kolling
    • 6
  • Antony R. Crofts
    • 1
  • Govindjee
    • 1
    • 7
  1. 1.Department of Biochemistry and Center for Biophysics and Computational BiologyUniversity of Illinois at Urbana-ChampaignUrbanaUSA
  2. 2.Institute of Low Temperature ScienceHokkaido UniversitySapporoJapan
  3. 3.Department of Natural Resources and Environmental Sciences (NRES)University of Illinois at Urbana-ChampaignUrbanaUSA
  4. 4.Physiological and Molecular Plant Biology ProgramUniversity of Illinois at Urbana-ChampaignUrbanaUSA
  5. 5.Department of Biochemistry, Molecular Biology and BiophysicsUniversity of MinnesotaMinneapolisUSA
  6. 6.Department of ChemistryPrinceton UniversityPrincetonUSA
  7. 7.Department of Plant BiologyUniversity of Illinois at Urbana-ChampaignUrbanaUSA