title: Tuning of Hemes b Equilibrium Redox Potential Is Not Required for Cross-Membrane Electron Transfer.
abstract: In biological energy conversion, cross-membrane electron transfer often involves an assembly of two hemesb The hemes display a large difference in redox midpoint potentials (ΔEm_b), which in several proteins is assumed to facilitate cross-membrane electron transfer and overcome a barrier of membrane potential. Here we challenge this assumption reporting on hemebligand mutants of cytochromebc1in which, for the first time in transmembrane cytochrome, one natural histidine has been replaced by lysine without loss of the native low spin type of heme iron. With these mutants we show that ΔEm_b can be markedly increased, and the redox potential of one of the hemes can stay above the level of quinone pool, or ΔEm_b can be markedly decreased to the point that two hemes are almost isopotential, yet the enzyme retains catalytically competent electron transfer between quinone binding sites and remains functionalin vivo This reveals that cytochromebc1can accommodate large changes in ΔEm_b without hampering catalysis, as long as these changes do not impose overly endergonic steps on downhill electron transfer from substrate to product. We propose that hemesbin this cytochrome and in other membranous cytochromesbact as electronic connectors for the catalytic sites with no fine tuning in ΔEm_b required for efficient cross-membrane electron transfer. We link this concept with a natural flexibility in occurrence of several thermodynamic configurations of the direction of electron flow and the direction of the gradient of potential in relation to the vector of the electric membrane potential.
authors: From the Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland.
authors: Sebastian
authors: S
authors: Pintscher
authors: From the Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland.
authors: Patryk
authors: P
authors: Kuleta
authors: From the Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland.
authors: Ewelina
authors: E
authors: Cieluch
authors: From the Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland.
authors: Arkadiusz
authors: A
authors: Borek
authors: From the Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland.
authors: Marcin
authors: M
authors: Sarewicz
authors: From the Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland artur.osyczka@uj.edu.pl.
authors: Artur
authors: A
authors: Osyczka
mesh_terms: D019943:Amino Acid Substitution; D001665:Binding Sites; D020134:Catalytic Domain; D004579:Electron Transport; D014450:Electron Transport Complex III / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004583:Electrons; D004926:Escherichia coli / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D015870:Gene Expression; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000235:genetics; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008239:Lysine / Q000737:chemistry / Q000235:genetics; D008564:Membrane Potentials / Q000502:physiology*; D009154:Mutation; D011809:Quinones / Q000737:chemistry / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D013816:Thermodynamics
chemical_list: D011809:Quinones; D006418:Heme; D006639:Histidine; D007501:Iron; D014450:Electron Transport Complex III; D008239:Lysine
keywords: cytochrome; electron transfer; heme iron ligation; oxidation-reduction (redox); photosynthesis; respiratory chain