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

AI Article Synopsis

  • Bacterial reaction centers convert light energy into chemical energy by facilitating the uptake of protons alongside the semi-reduction of two quinones (Q(A) and Q(B)), which are symmetrically arranged around a non-heme iron atom.
  • In a study using variants M234EH and M234EL, researchers examined how the acidic residue M234Glu influences the energy balance and proton uptake between quinones, finding that both quinones are equally destabilized compared to the wild-type reaction center.
  • The significance of M234Glu is highlighted by the observed loss of a high pH band linked to proton uptake in the variants, indicating its vital role in a cohesive proton uptake network within the reaction center.

Article Abstract

Bacterial reaction centers use light energy to couple the uptake of protons to the successive semi-reduction of two quinones, namely Q(A) and Q(B). 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(+)Q(A)(-) state (P is the primary electron donor) and temperature dependence of the rate of P(+)Q(A)(-) charge recombination that are in good agreement show that in the two RC variants, both Q(A)(-) and Q(B)(-) are destabilized by about the same free energy amount: respectively approximately 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 Q(A)(-) and Q(B)(-). 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.

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Source
http://dx.doi.org/10.1016/j.bbabio.2009.07.004DOI Listing

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