Identification of amino acid residues in a proton release pathway near the bacteriochlorophyll dimer in reaction centers from Rhodobacter sphaeroides

J. P. Allen, K. D. Chamberlain, J. C. Williams

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Insight into control of proton transfer, a crucial attribute of cellular functions, can be gained from investigations of bacterial reaction centers. While the uptake of protons associated with the reduction of the quinone is well characterized, the release of protons associated with the oxidized bacteriochlorophyll dimer has been poorly understood. Optical spectroscopy and proton release/uptake measurements were used to examine the proton release characteristics of twelve mutant reaction centers, each containing a change in an amino acid residue near the bacteriochlorophyll dimer. The mutant reaction centers had optical spectra similar to wild-type and were capable of transferring electrons to the quinones after light excitation of the bacteriochlorophyll dimer. They exhibited a large range in the extent of proton release and in the slow recovery of the optical signal for the oxidized dimer upon continuous illumination. Key roles were indicated for six amino acid residues, Thr L130, Asp L155, Ser L244, Arg M164, Ser M190, and His M193. Analysis of the results points to a hydrogen-bond network that contains these residues, with several additional residues and bound water molecules, forming a proton transfer pathway. In addition to proton transfer, the properties of the pathway are proposed to be responsible for the very slow charge recombination kinetics observed after continuous illumination. The characteristics of this pathway are compared to proton transfer pathways near the secondary quinone as well as those found in photosystem II and cytochrome c oxidase.

Original languageEnglish (US)
Pages (from-to)23-34
Number of pages12
JournalPhotosynthesis research
Volume155
Issue number1
DOIs
StatePublished - Jan 2023
Externally publishedYes

Keywords

  • Optical spectroscopy
  • Photosynthesis
  • Proton transfer
  • Proton-coupled electron transfer
  • Purple bacteria

ASJC Scopus subject areas

  • Biochemistry
  • Plant Science
  • Cell Biology

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