TY - JOUR
T1 - Directing electron transfer within Photosystem I by breaking H-bonds in the cofactor branches
AU - Li, Yajing
AU - Van Der Est, Art
AU - Lucas, Marie Gabrielle
AU - Ramesh, V. M.
AU - Gu, Feifei
AU - Petrenko, Alexander
AU - Lin, Su
AU - Webber, Andrew
AU - Rappaport, Fabrice
AU - Redding, Kevin
PY - 2006/2/14
Y1 - 2006/2/14
N2 - Photosystem I has two branches of cofactors down which light-driven electron transfer (ET) could potentially proceed, each consisting of a pair of chlorophylls (Chls) and a phylloquinone (PhQ). Forward ET from PhQ to the next ET cofactor (Fx) is described by two kinetic components with decay times of ≈20 and ≈200 ns, which have been proposed to represent ET from PhQB and PhQA, respectively. Immediately preceding each quinone is a Chl (ec3), which receives a H-bond from a nearby tyrosine. To decrease the reduction potential of each of these Chls, and thus modify the relative yield of ET within the targeted branch, this H-bond was removed by conversion of each Tyr to Phe in the green alga Chlamydomonas reinhardtii. Together, transient optical absorption spectroscopy performed in vivo and transient electron paramagnetic resonance data from thylakoid membranes showed that the mutations affect the relative amplitudes, but not the lifetimes, of the two kinetic components representing ET from PhQ to Fx. The mutation near ec3A increases the fraction of the faster component at the expense of the slower component, with the opposite effect seen in the ec3B mutant. We interpret this result as a decrease in the relative use of the targeted branch. This finding suggests that in Photosystem I, unlike type II reaction centers, the relative efficiency of the two branches is extremely sensitive to the energetics of the embedded redox cofactors.
AB - Photosystem I has two branches of cofactors down which light-driven electron transfer (ET) could potentially proceed, each consisting of a pair of chlorophylls (Chls) and a phylloquinone (PhQ). Forward ET from PhQ to the next ET cofactor (Fx) is described by two kinetic components with decay times of ≈20 and ≈200 ns, which have been proposed to represent ET from PhQB and PhQA, respectively. Immediately preceding each quinone is a Chl (ec3), which receives a H-bond from a nearby tyrosine. To decrease the reduction potential of each of these Chls, and thus modify the relative yield of ET within the targeted branch, this H-bond was removed by conversion of each Tyr to Phe in the green alga Chlamydomonas reinhardtii. Together, transient optical absorption spectroscopy performed in vivo and transient electron paramagnetic resonance data from thylakoid membranes showed that the mutations affect the relative amplitudes, but not the lifetimes, of the two kinetic components representing ET from PhQ to Fx. The mutation near ec3A increases the fraction of the faster component at the expense of the slower component, with the opposite effect seen in the ec3B mutant. We interpret this result as a decrease in the relative use of the targeted branch. This finding suggests that in Photosystem I, unlike type II reaction centers, the relative efficiency of the two branches is extremely sensitive to the energetics of the embedded redox cofactors.
KW - Chlamydomonas
KW - Directionality
KW - Photosynthetic reaction center
KW - Pump-probe spectroscopy
KW - Transient EPR
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U2 - 10.1073/pnas.0506537103
DO - 10.1073/pnas.0506537103
M3 - Article
C2 - 16467143
AN - SCOPUS:33144464784
SN - 0027-8424
VL - 103
SP - 2144
EP - 2149
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 7
ER -