title: Proton uptake in the reaction center mutant L210DN from Rhodobacter sphaeroides via protonated water molecules.
abstract: The reaction center (RC) of Rhodobacter sphaeroides uses light energy to reduce and protonate a quinone molecule, QB (the secondary quinone electron acceptor), to form quinol, QBH2. Asp210 in the L-subunit has been shown to be a catalytic residue in this process. Mutation of Asp210 to Asn leads to a deceleration of reoxidation of QA- in the QA-QB --> QAQB- transition. Here we determined the structure of the Asp210 to Asn mutant to 2.5 A and show that there are no major structural differences as compared to the wild-type protein. We found QB in the distal position and a chain of water molecules between Asn210 and QB. Using time-resolved Fourier transform infrared (trFTIR) spectroscopy, we characterized the molecular reaction mechanism of this mutant. We found that QB- formation precedes QA- oxidation even more pronounced than in the wild-type reaction center. Continuum absorbance changes indicate deprotonation of a protonated water cluster, most likely of the water chain between Asn210 and QB. A detailed analysis of wild-type structures revealed a highly conserved water chain between Asp210 or Glu210 and QB in Rb. sphaeroides and Rhodopseudomonas viridis, respectively.
authors.affiliation: Lehrstuhl für Biophysik, ND 04/596, Ruhr-Universität Bochum, D-44801 Bochum, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Hermes
authors.forename: Joanna M
authors.initials: JM
authors.lastname: Stachnik
authors.forename: Delphine
authors.initials: D
authors.lastname: Onidas
authors.forename: André
authors.initials: A
authors.lastname: Remy
authors.forename: Eckhard
authors.initials: E
authors.lastname: Hofmann
authors.forename: Klaus
authors.initials: K
authors.lastname: Gerwert
mesh_terms: D004583:Electrons; D008958:Models, Molecular; D009154:Mutation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D011522:Protons; D012242:Rhodobacter sphaeroides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons; D014867:Water