Regulation of the Primary Quinone Binding Conformation by the H Subunit in Reaction Centers from Rhodobacter sphaeroides

Chang Sun, Alexander T. Taguchi, Nathan J. Beal, Patrick J. Omalley, Sergei A. Dikanov, Colin A. Wraight

Research output: Contribution to journalArticlepeer-review

Abstract

Unlike photosystem II (PSII) in higher plants, bacterial photosynthetic reaction centers (bRCs) from Proteobacteria have an additional peripheral membrane subunit "H". The H subunit is necessary for photosynthetic growth, but can be removed chemically in vitro. The remaining LM dimer retains its activity to perform light-induced charge separation. Here we investigate the influence of the H subunit on interactions between the primary semiquinone and the protein matrix, using a combination of site-specific isotope labeling, pulsed electron paramagnetic resonance (EPR), and density functional theory (DFT) calculations. The data reveal substantially weaker binding interactions between the primary semiquinone and the LM dimer than observed for the intact bRC; the amount of electron spin transferred to the nitrogen hydrogen bond donors is significantly reduced, the methoxy groups are more free to rotate, and the spectra indicate a heterogeneous mixture of bound semiquinone states. These results are consistent with a loosening of the primary quinone binding pocket in the absence of the H subunit.

Original languageEnglish (US)
Pages (from-to)4521-4546
Number of pages26
JournalJournal of Physical Chemistry Letters
Volume6
Issue number22
DOIs
StatePublished - Nov 19 2015

Keywords

  • DFT
  • hyperfine coupling
  • isotope labeling
  • pulsed EPR
  • site-directed mutagenesis
  • ubisemiquinone

ASJC Scopus subject areas

  • Materials Science(all)
  • Physical and Theoretical Chemistry

Fingerprint Dive into the research topics of 'Regulation of the Primary Quinone Binding Conformation by the H Subunit in Reaction Centers from Rhodobacter sphaeroides'. Together they form a unique fingerprint.

Cite this