Quinone-dependent proton transfer pathways in the photosynthetic cytochrome b6f complex.

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TitleQuinone-dependent proton transfer pathways in the photosynthetic cytochrome b6f complex.
Publication TypeJournal Article
Year of Publication2013
AuthorsS Hasan, S, Yamashita, E, Baniulis, D, Cramer, WA
JournalProc Natl Acad Sci U S A
Date Published2013 Mar 12
KeywordsBenzoquinones, Chlamydomonas reinhardtii, Cytochrome b6f Complex, Heme, Ion Transport, Membrane Potentials, Protein Structure, Quaternary, Protein Structure, Tertiary, Protons

As much as two-thirds of the proton gradient used for transmembrane free energy storage in oxygenic photosynthesis is generated by the cytochrome b6f complex. The proton uptake pathway from the electrochemically negative (n) aqueous phase to the n-side quinone binding site of the complex, and a probable route for proton exit to the positive phase resulting from quinol oxidation, are defined in a 2.70-Å crystal structure and in structures with quinone analog inhibitors at 3.07 Å (tridecyl-stigmatellin) and 3.25-Å (2-nonyl-4-hydroxyquinoline N-oxide) resolution. The simplest n-side proton pathway extends from the aqueous phase via Asp20 and Arg207 (cytochrome b6 subunit) to quinone bound axially to heme c(n). On the positive side, the heme-proximal Glu78 (subunit IV), which accepts protons from plastosemiquinone, defines a route for H(+) transfer to the aqueous phase. These pathways provide a structure-based description of the quinone-mediated proton transfer responsible for generation of the transmembrane electrochemical potential gradient in oxygenic photosynthesis.

Alternate JournalProc. Natl. Acad. Sci. U.S.A.
PubMed ID23440205
PubMed Central IDPMC3600468
Grant ListR01 GM038323 / GM / NIGMS NIH HHS / United States
R56 GM038323 / GM / NIGMS NIH HHS / United States
GM-038323 / GM / NIGMS NIH HHS / United States