Certain metal ions are inhibitors of cytochrome b6f complex 'Rieske' iron-sulfur protein domain movements

Biochemistry
Arthur G RobertsDavid M Kramer

Abstract

Many current models of the Q cycle for the cytochrome (cyt) b6f and the cyt bc1 complexes incorporate 'Rieske' iron-sulfur protein (ISP) domain movements to gate electron transfer and to ensure high yields of proton shuttling. It was previously proposed that copper ions, which bind at a site distant from the quinol oxidase (Q(o)) site, inhibit plastoquinol (PQH2) binding by restraining the hydrophilic head domain of the ISP [Rao B. K., S., Tyryshkin, A. M., Roberts, A. G., Bowman, M. K., and Kramer, D. M. (1999) Biochemistry 38, 3285-3296]. The present work presents evidence that this is indeed the case for both copper ions and Zn2+, which appear to inhibit by similar mechanisms. Electron paramagnetic resonance (EPR) spectra show that Cu2+ and Zn2+ binding to the cyt b6f complex displaces the Q(o) site inhibitor 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB). At high concentrations, both DBMIB and Cu2+ or Zn2+ can bind simultaneously, altering the Rieske 2Fe2S cluster and Cu2+ EPR spectra, suggesting perturbations in their respective binding sites. Both Zn2+ and Cu1+ altered the orientations of the Rieske 2Fe2S cluster with respect to the membrane plane, but had no effect on that of the cyt b6 hemes. Cu2+ was found to cha...Continue Reading

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Citations

May 23, 2013·Photosynthesis Research·Alexander N Tikhonov
Feb 4, 2014·Plant Physiology and Biochemistry : PPB·Alexander N Tikhonov
May 15, 2007·Journal of Molecular Biology·E YamashitaW A Cramer
Jan 25, 2017·Proceedings of the National Academy of Sciences of the United States of America·Marcin SarewiczArtur Osyczka
Dec 15, 2005·Trends in Plant Science·Jonathan L CapeDavid M Kramer
Oct 22, 2003·Accounts of Chemical Research·Manuel HervásMiguel A De La Rosa

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