Strong effects of an individual water molecule on the rate of light-driven charge separation in the Rhodobacter sphaeroides reaction center

JA Potter, PK Fyfe, D Frolov, MC Wakeham, R van Grondelle, B Robert, MR Jones*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)

Abstract

The role of a water molecule (water A) located between the primary electron donor (P) and first electron acceptor bacteriochlorophyll (B-A) in the purple bacterial reaction center was investigated by mutation of glycine M203 to leucine (GM203L). The x-ray crystal structure of the GM203L reaction center shows that the new leucine residue packs in such a way that water A is sterically excluded from the complex, but the structure of the protein-cofactor system around the mutation site is largely undisturbed. The results of absorbance and resonance Raman spectroscopy were consistent with either the removal of a hydrogen bond interaction between water A and the keto carbonyl group of B-A or a change in the local electrostatic environment of this carbonyl group. Similarities in the spectroscopic properties and x-ray crystal structures of reaction centers with leucine and aspartic acid mutations at the M203 position suggested that the effects of a glycine to aspartic acid substitution at the M203 position can also be explained by steric exclusion of water A. In the GM203L mutant, loss of water A was accompanied by an similar to 8-fold slowing of the rate of decay of the primary donor excited state, indicating that the presence of water A is important for optimization of the rate of primary electron transfer. Possible functions of this water molecule are discussed, including a switching role in which the redox potential of the B-A acceptor is rapidly modulated in response to oxidation of the primary electron donor.

Original languageEnglish
Pages (from-to)27155-27164
Number of pages10
JournalJournal of Biological Chemistry
Volume280
Issue number29
DOIs
Publication statusPublished - 22 Jul 2005

Keywords

  • PHOTOSYNTHETIC REACTION-CENTER
  • BACTERIAL REACTION CENTERS
  • BOUND REACTION CENTERS
  • RESONANCE RAMAN-SPECTROSCOPY
  • PRIMARY ELECTRON-DONOR
  • RHODOPSEUDOMONAS-VIRIDIS
  • CRYSTAL-STRUCTURES
  • BACTERIOCHLOROPHYLL DIMER
  • ANGSTROM RESOLUTION
  • OPTICAL-PROPERTIES

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