title: Intermonomer electron transfer between the b hemes of heterodimeric cytochrome bc(1).
abstract: The ubihydroquinone:cytochrome c oxidoreductase, or cytochrome bc1, is a central component of respiratory and photosynthetic energy transduction pathways in many organisms. It contributes to the generation of membrane potential and proton gradient used for cellular energy (ATP) production. The three-dimensional structures of cytochrome bc1 show a homodimeric organization of its three catalytic subunits. The unusual architecture revived the issue of whether the monomers operate independently or function cooperatively during the catalytic cycle of the enzyme. In recent years, different genetic approaches allowed the successful production of heterodimeric cytochrome bc1 variants and evidenced the occurrence of intermonomer electron transfer between the monomers of this enzyme. Here we used a version of the "two-plasmid" genetic system, also described in the preceding paper (DOI: 10.1021/bi400560p), to study a new heterodimeric mutant variant of cytochrome bc1. The strain producing this heterodimeric variant sustained photosynthetic growth of Rhodobacter capsulatus and yielded an active heterodimer. Interestingly, kinetic data showed equilibration of electrons among the four b heme cofactors of the heterodimer, via "reverse" intermonomer electron transfer between the bL hemes. Both inactive homodimeric and active heterodimeric cytochrome bc1 variants were purified to homogeneity from the same cells, and purified samples were subjected to mass spectrometry analyses. The data unequivocally supported the idea that the cytochrome b subunits carried the expected mutations and their associated epitope tags. Implications of these findings on our interpretation of light-activated transient cytochrome b and c redox kinetics and the mechanism of function of a dimeric cytochrome bc1 are discussed with respect to the previously proposed heterodimeric Q cycle model.
authors.affiliation: Department of Biology, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Pascal
authors.initials: P
authors.lastname: Lanciano
authors.forename: Bahia
authors.initials: B
authors.lastname: Khalfaoui-Hassani
authors.forename: Nur
authors.initials: N
authors.lastname: Selamoglu
authors.forename: Fevzi
authors.initials: F
authors.lastname: Daldal
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D016354:Rhodobacter capsulatus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D006418:Heme; D014450:Electron Transport Complex III
references.citation: Photosynth Res. 2004;81(3):251-75
references.pmid: 16034531
references.citation: Biochim Biophys Acta. 2002 Sep 10;1555(1-3):166-73
references.pmid: 12206910
references.citation: Biochemistry. 1994 Jan 25;33(3):723-33
references.pmid: 8292600
references.citation: Biochim Biophys Acta. 1982 Jul 22;681(1):41-53
references.pmid: 6288082
references.citation: Biochemistry. 2011 Mar 15;50(10):1651-63
references.pmid: 21261281
references.citation: J Biol Chem. 2007 Aug 17;282(33):24198-208
references.pmid: 17584742
references.citation: J Biol Chem. 2010 Jan 1;285(1):502-10
references.pmid: 19892700
references.citation: J Theor Biol. 1976 Oct 21;62(2):327-67
references.pmid: 186667
references.citation: Biochemistry. 2003 Feb 18;42(6):1499-507
references.pmid: 12578362
references.citation: Proc Natl Acad Sci U S A. 1991 Jan 15;88(2):492-6
references.pmid: 1846443
references.citation: Biochemistry. 1995 Dec 12;34(49):16004-12
references.pmid: 8519756
references.citation: Science. 1997 Jul 4;277(5322):60-6
references.pmid: 9204897
references.citation: FEBS Lett. 1998 Jul 17;431(2):291-6
references.pmid: 9708922
references.citation: Biochemistry. 2005 Aug 9;44(31):10520-32
references.pmid: 16060661
references.citation: Science. 1998 Jul 3;281(5373):64-71
references.pmid: 9651245
references.citation: J Biol Chem. 2002 Feb 1;277(5):3464-70
references.pmid: 11707448
references.citation: Nature. 1970 Aug 15;227(5259):680-5
references.pmid: 5432063
references.citation: Biochemistry. 2009 Mar 10;48(9):1888-99
references.pmid: 19254042
references.citation: Nature. 2004 Feb 12;427(6975):607-12
references.pmid: 14961113
references.citation: J Mol Biol. 1987 May 5;195(1):1-12
references.pmid: 2821266
references.citation: Annu Rev Biochem. 2000;69:1005-75
references.pmid: 10966481
references.citation: FEBS Lett. 2012 Mar 9;586(5):617-21
references.pmid: 21878327
references.citation: Mol Cell Proteomics. 2008 May;7(5):875-90
references.pmid: 18174153
references.citation: Biochemistry. 2011 Dec 6;50(48):10462-72
references.pmid: 22026826
references.citation: J Biol Chem. 1990 Jul 15;265(20):11409-12
references.pmid: 2164001
references.citation: Biochemistry. 1998 Nov 17;37(46):16242-51
references.pmid: 9819216
references.citation: Biochim Biophys Acta. 1983 May 23;723(2):202-218
references.pmid: 21494412
references.citation: Biochim Biophys Acta. 2010 Dec;1797(12):1842-8
references.pmid: 20513347
references.citation: Biochemistry. 2012 Jan 31;51(4):829-35
references.pmid: 22233445
references.citation: Science. 2010 Jul 23;329(5990):451-4
references.pmid: 20651150
references.citation: Photosynth Res. 2004;80(1-3):223-43
references.pmid: 16328823
references.citation: Anal Biochem. 1985 Oct;150(1):76-85
references.pmid: 3843705
references.citation: Biochemistry. 1995 Dec 12;34(49):15979-96
references.pmid: 8519754
references.citation: Biochemistry. 1992 Dec 1;31(47):11864-73
references.pmid: 1332776
references.citation: Biochemistry. 1995 Dec 12;34(49):15997-6003
references.pmid: 8519755