TY - JOUR
T1 - Interquinone electron transfer in photosystem i as evidenced by altering the hydrogen bond strength to the phylloquinone(s)
AU - Santabarbara, Stefano
AU - Reifschneider, Kiera
AU - Jasaitis, Audrius
AU - Gu, Feifei
AU - Agostini, Giancarlo
AU - Carbonera, Donatella
AU - Rappaport, Fabrice
AU - Redding, Kevin
PY - 2010/7/22
Y1 - 2010/7/22
N2 - The kinetics of electron transfer from phyllosemiquinone (PhQ ̇-) to the iron sulfur cluster FX in Photosystem I (PS I) are described by lifetimes of ∼20 and ∼250 ns. These two rates are attributed to reactions involving the quinones bound primarily by the PsaB (PhQB) and PsaA (PhQA) subunits, respectively. The factors leading to a ∼10-fold difference between the observed lifetimes are not yet clear. The peptide nitrogen of conserved residues PsaA-Leu722 and PsaB-Leu706 is involved in asymmetric hydrogen-bonding to PhQA and PhQ B, respectively. Upon mutation of these residues in PS I of the green alga, Chlamydomonas reinhardtii, we observe an acceleration of the oxidation kinetics of the PhQ̇- interacting with the targeted residue: from ∼255 to ∼180 ns in PsaA-L722Y/T and from ∼24 to ∼10 ns in PsaB-L706Y. The acceleration of the kinetics in the mutants is consistent with a perturbation of the H-bond, destabilizing the PhQ̇- state, and increasing the driving force of its oxidation. Surprisingly, the relative amplitudes of the phases reflecting PhQȦ- and PhQḂ- oxidation were also affected by these mutations: the apparent PhQȦ-/PhQB ̇- ratio is shifted from 0.65:0.35 in wild-type reaction centers to 0.5:0.5 in PsaA-L722Y/T and to 0.8:0.2 in PsaB-L706Y. The most consistent account for all these observations involves considering reversibility of oxidation of PhQȦ- and PhQB ̇- by FX, and asymmetry in the driving forces for these electron transfer reactions, which in turn leads to Fx-mediated interquinone electron transfer.
AB - The kinetics of electron transfer from phyllosemiquinone (PhQ ̇-) to the iron sulfur cluster FX in Photosystem I (PS I) are described by lifetimes of ∼20 and ∼250 ns. These two rates are attributed to reactions involving the quinones bound primarily by the PsaB (PhQB) and PsaA (PhQA) subunits, respectively. The factors leading to a ∼10-fold difference between the observed lifetimes are not yet clear. The peptide nitrogen of conserved residues PsaA-Leu722 and PsaB-Leu706 is involved in asymmetric hydrogen-bonding to PhQA and PhQ B, respectively. Upon mutation of these residues in PS I of the green alga, Chlamydomonas reinhardtii, we observe an acceleration of the oxidation kinetics of the PhQ̇- interacting with the targeted residue: from ∼255 to ∼180 ns in PsaA-L722Y/T and from ∼24 to ∼10 ns in PsaB-L706Y. The acceleration of the kinetics in the mutants is consistent with a perturbation of the H-bond, destabilizing the PhQ̇- state, and increasing the driving force of its oxidation. Surprisingly, the relative amplitudes of the phases reflecting PhQȦ- and PhQḂ- oxidation were also affected by these mutations: the apparent PhQȦ-/PhQB ̇- ratio is shifted from 0.65:0.35 in wild-type reaction centers to 0.5:0.5 in PsaA-L722Y/T and to 0.8:0.2 in PsaB-L706Y. The most consistent account for all these observations involves considering reversibility of oxidation of PhQȦ- and PhQB ̇- by FX, and asymmetry in the driving forces for these electron transfer reactions, which in turn leads to Fx-mediated interquinone electron transfer.
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U2 - 10.1021/jp1038656
DO - 10.1021/jp1038656
M3 - Article
C2 - 20583790
AN - SCOPUS:77954709177
SN - 1520-6106
VL - 114
SP - 9300
EP - 9312
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 28
ER -