TY - JOUR
T1 - EPR, ENDOR, and Special TRIPLE measurements of P•+ in wild type and modified reaction centers from Rb. sphaeroides
AU - Allen, James
AU - Cordova, J. M.
AU - Jolley, C. C.
AU - Murray, T. A.
AU - Schneider, J. W.
AU - Woodbury, Neal
AU - Williams, Joann
AU - Niklas, J.
AU - Klihm, G.
AU - Reus, M.
AU - Lubitz, W.
N1 - Funding Information:
Acknowledgments Student support for this project was provided by the ASU’s IGERT in Biomolecular Nanotechnology, funded by the NSF (DGE-0114434). As part of this project, students were able to prepare samples at ASU and spend time performing research in Mülheim/Ruhr. In addition, students also performed FTIR measurements in Saclay with Eliane Nabedryk and Jacques Breton; we gratefully acknowledge their hospitality during this work. Alexey Silakov (MPI Mülheim) is acknowledged for writing the Matlab routine to analyze the Special TRIPLE spectra. The work was partially supported from the NSF (MCB0640002 and MCB0642260) and from the Max Planck Society.
PY - 2009/1
Y1 - 2009/1
N2 - The influence of the protein environment on the primary electron donor, P, a bacteriochlorophyll a dimer, of reaction centers from Rhodobacter sphaeroides, has been investigated using electron paramagnetic resonance and electron nuclear double resonance spectroscopy. These techniques were used to probe the effects on P that are due to alteration of three amino acid residues, His L168, Asn L170, and Asn M199. The introduction of Glu at L168, Asp at L170, or Asp at M199 changes the oxidation/reduction midpoint potential of P in a pH-dependent manner (Williams et al. (2001) Biochemistry 40, 15403-15407). For the double mutant His L168 to Glu and Asn at L170 to Asp, excitation results in electron transfer along the A-side branch of cofactors at pH 7.2, but at pH 9.5, a long-lived state involving B-side cofactors is produced (Haffa et al. (2004) J Phys Chem B 108, 4-7). Using electron paramagnetic resonance spectroscopy, the mutants with alterations of each of the three individual residues and a double mutant, with changes at L168 and L170, were found to have increased linewidths of 10.1-11.0 G compared to the linewidth of 9.6 G for wild type. The Special TRIPLE spectra were pH dependent, and at pH 8, the introduction of aspartate at L170 increased the spin density ratio, ρ L/ρ M, to 6.1 while an aspartate at the symmetry related position, M199, decreased the ratio to 0.7 compared to the value of 2.1 for wild type. These results indicate that the energy of the two halves of P changes by about 100 meV due to the mutations and are consistent with the interpretation that electrostatic interactions involving these amino acid residues contribute to the switch in pathway of electron transfer.
AB - The influence of the protein environment on the primary electron donor, P, a bacteriochlorophyll a dimer, of reaction centers from Rhodobacter sphaeroides, has been investigated using electron paramagnetic resonance and electron nuclear double resonance spectroscopy. These techniques were used to probe the effects on P that are due to alteration of three amino acid residues, His L168, Asn L170, and Asn M199. The introduction of Glu at L168, Asp at L170, or Asp at M199 changes the oxidation/reduction midpoint potential of P in a pH-dependent manner (Williams et al. (2001) Biochemistry 40, 15403-15407). For the double mutant His L168 to Glu and Asn at L170 to Asp, excitation results in electron transfer along the A-side branch of cofactors at pH 7.2, but at pH 9.5, a long-lived state involving B-side cofactors is produced (Haffa et al. (2004) J Phys Chem B 108, 4-7). Using electron paramagnetic resonance spectroscopy, the mutants with alterations of each of the three individual residues and a double mutant, with changes at L168 and L170, were found to have increased linewidths of 10.1-11.0 G compared to the linewidth of 9.6 G for wild type. The Special TRIPLE spectra were pH dependent, and at pH 8, the introduction of aspartate at L170 increased the spin density ratio, ρ L/ρ M, to 6.1 while an aspartate at the symmetry related position, M199, decreased the ratio to 0.7 compared to the value of 2.1 for wild type. These results indicate that the energy of the two halves of P changes by about 100 meV due to the mutations and are consistent with the interpretation that electrostatic interactions involving these amino acid residues contribute to the switch in pathway of electron transfer.
KW - Bacteriochlorophyll
KW - Electron paramagnetic resonance
KW - Magnetic resonance
KW - Oxidized bacteriochlorophyll dimer
KW - Purple bacteria
KW - Reaction centers
UR - http://www.scopus.com/inward/record.url?scp=57849160617&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=57849160617&partnerID=8YFLogxK
U2 - 10.1007/s11120-008-9346-6
DO - 10.1007/s11120-008-9346-6
M3 - Article
C2 - 18819016
AN - SCOPUS:57849160617
SN - 0166-8595
VL - 99
SP - 1
EP - 10
JO - Photosynthesis research
JF - Photosynthesis research
IS - 1
ER -