Modeling the Effects of Mutations on the Free Energy of the First Electron Transfer from QA- to QB in Photosynthetic Reaction Centers
- 29 April 2000
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 39 (20) , 5940-5952
- https://doi.org/10.1021/bi9929498
Abstract
Numerical calculations of the free energy of the first electron transfer in genetically modified reaction centers from Rhodobacter (Rb.) sphaeroides and Rb. capsulatus were carried out from pH 5 to 11. The multiconformation continuum electrostatics (MCCE) method allows side chain, ligand, and water reorientation to be embedded in the calculations of the Boltzmann distribution of cofactor and amino acid ionization states. The mutation sites whose effects have been modeled are L212 and L213 (the L polypeptide) and two in the M polypeptide, M43(44) and M231(233) in Rb. capsulatus (Rb. sphaeroides). The results of the calculations were compared to the experimental data, and very good agreement was found especially at neutral pH. Each mutation removes or introduces ionizable residues, but the protein maintains a net charge close to that in native RCs through ionization changes in nearby residues. This reduces the effect of mutation and makes the changes in state free energy smaller than would be found in a rigid protein. The state energy of QA-QB and QAQB- states have contributions from interactions among the residues as well as with the quinone which is ionized. For example, removing L213Asp, located in the QB pocket, predominantly changes the free energy of the QA-QB state, where the Asp is ionized in native RCs rather than the QAQB- state, where it is neutral. Side chain, hydroxyl, and water rearrangements due to each of the mutations have also been calculated showing water occupancy changes during the QA- to QB electron transfer.Keywords
This publication has 21 references indexed in Scilit:
- Modeling of protein conformational fluctuations in pKa predictionsJournal of Molecular Biology, 1997
- Coupling Between Folding and Ionization Equilibria: Effects of pH on the Conformational Preferences of PolypeptidesJournal of Molecular Biology, 1996
- The fast multipole boundary element method for molecular electrostatics: An optimal approach for large systemsJournal of Computational Chemistry, 1995
- Electrostatic calculations of amino acid titration and electron transfer, Q-AQB-->QAQ-B, in the reaction centerBiophysical Journal, 1995
- In bacterial reaction centers protons can diffuse to the secondary quinone by alternative pathwaysBiochimica et Biophysica Acta (BBA) - Bioenergetics, 1992
- A crucial role for AspL213 in the proton transfer pathway to the secondary quinone of reaction centers from Rhodobacter sphaeroidesBiochimica et Biophysica Acta (BBA) - Bioenergetics, 1990
- Electrostatic control of charge separation in bacterial photosynthesisBiochimica et Biophysica Acta (BBA) - Bioenergetics, 1990
- Light-induced proton uptake by photosynthetic reaction centers from Rhodobacter sphaeroides R-26. I. Protonation of the one-electron states D+QA−, DQA−, D+QAQB−, and DQAQB−Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1988
- Electron transfer in reaction centers of Rhodopseudomonas sphaeroides. I. Determination of the charge recombination pathway of D+QAQ−B and free energy and kinetic relations between Q−AQB and QAQ−BBiochimica et Biophysica Acta (BBA) - Bioenergetics, 1984
- Electron acceptors of bacterial photosynthetic reaction centers II. H+ binding coupled to secondary electron transfer in the quinone acceptor complexBiochimica et Biophysica Acta (BBA) - Bioenergetics, 1979