title: Inter-monomer electron transfer is too slow to compete with monomeric turnover in bc(1) complex.
abstract: The homodimeric bc(1) complexes are membrane proteins essential in respiration and photosynthesis. The ~11Å distance between the two b(L)-hemes of the dimer opens the possibility of electron transfer between them, but contradictory reports make such inter-monomer electron transfer controversial. We have constructed in Rhodobacter sphaeroides a heterodimeric expression system similar to those used before, in which the bc(1) complex can be mutated differentially in the two copies of cyt b to test for inter-monomer electron transfer, but found that genetic recombination by cross-over then occurs to produce wild-type homodimer. Selection pressure under photosynthetic growth always favored the homodimer over heterodimeric variants enforcing inter-monomer electron transfer, showing that the latter are not competitive. These results, together with kinetic analysis of myxothiazol titrations, demonstrate that inter-monomer electron transfer does not occur at rates competitive with monomeric turnover. We examine the results from other groups interpreted as demonstrating rapid inter-monomer electron transfer, conclude that similar mechanisms are likely to be in play, and suggest that such claims might need to be re-examined.
authors.affiliation: Departments of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. hong6345@illinois.edu
authors.forename: Sangjin
authors.initials: S
authors.lastname: Hong
authors.forename: Doreen
authors.initials: D
authors.lastname: Victoria
authors.forename: Antony R
authors.initials: AR
authors.lastname: Crofts
mesh_terms: D003434:Crossing Over, Genetic / Q000187:drug effects; D004579:Electron Transport / Q000187:drug effects; D014450:Electron Transport Complex III / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008689:Methacrylates / Q000494:pharmacology; D050296:Microbial Viability / Q000187:drug effects; D008954:Models, Biological; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D055503:Protein Multimerization / Q000187:drug effects; D021122:Protein Subunits / Q000235:genetics; D012242:Rhodobacter sphaeroides / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D013844:Thiazoles / Q000494:pharmacology
chemical_list: D008689:Methacrylates; D021122:Protein Subunits; D013844:Thiazoles; C030517:myxothiazol; D014450:Electron Transport Complex III