M234Glu is a component of the proton sponge in the reaction center from photosynthetic bacteria

Hélène Cheap, Sophie Bernad, Valérie Derrien, László Gerencsér, Julia Tandori, Pedro de Oliveira, Deborah K. Hanson, Péter Maróti, Pierre Sebban

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Bacterial reaction centers use light energy to couple the uptake of protons to the successive semi-reduction of two quinones, namely QA and QB. These molecules are situated symmetrically in regard to a non-heme iron atom. Four histidines and one glutamic acid, M234Glu, constitute the five ligands of this atom. By flash-induced absorption spectroscopy and delayed fluorescence we have studied in the M234EH and M234EL variants the role played by this acidic residue on the energetic balance between the two quinones as well as in proton uptake. Delayed fluorescence from the P+QA- state (P is the primary electron donor) and temperature dependence of the rate of P+QA- charge recombination that are in good agreement show that in the two RC variants, both QA- and QB- are destabilized by about the same free energy amount: respectively ∼ 100 ± 5 meV and 90 ± 5 meV for the M234EH and M234EL variants, as compared to the WT. Importantly, in the M234EH and M234EL variants we observe a collapse of the high pH band (present in the wild-type reaction center) of the proton uptake amplitudes associated with formation of QA- and QB-. This band has recently been shown to be a signature of a collective behaviour of an extended, multi-entry, proton uptake network. M234Glu seems to play a central role in the proton sponge-like system formed by the RC protein.

Original languageEnglish
Pages (from-to)1505-1515
Number of pages11
JournalBiochimica et Biophysica Acta - Bioenergetics
Issue number12
Publication statusPublished - Dec 1 2009


  • Bioenergetics
  • Electron transfer
  • Hydrogen-bond network
  • Photosynthesis
  • Proton transfer
  • Reaction center

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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    Cheap, H., Bernad, S., Derrien, V., Gerencsér, L., Tandori, J., de Oliveira, P., Hanson, D. K., Maróti, P., & Sebban, P. (2009). M234Glu is a component of the proton sponge in the reaction center from photosynthetic bacteria. Biochimica et Biophysica Acta - Bioenergetics, 1787(12), 1505-1515. https://doi.org/10.1016/j.bbabio.2009.07.004