Rieske/Cytochrome b Complexes: The Turbo Chargers of Chemiosmosis
Rieske/cytochrome b complexes are transmembrane enzymes of many bioenergetic reaction chains. They operate according to a Q-cycle mechanism that allows the transfer of an extra proton over the membrane per electron transferred along the chain. Thus they optimize the ATP yield from the terminal electron donor/acceptor couples of the respective reaction chains. Two members of this family of enzymes, cytochrome bc 1 complex from proteobacteria and mitochondria and cytochrome b 6 f complex from cyanobacteria and chloroplast are well studied and crystal structures are available. While revealing unexpected features of the complexes, as the domain movement of the Rieske iron/sulfur protein and the presence of an unusual heme cofactor in a quinone binding pocket, they opened up new questions concerning the function of the enzyme. Few structural and functional studies are available for Rieske/cytb complexes from further species, which is the vast majority of bacterial and archeael phyla, and most information comes from genome analysis. Here we discuss structure and function of the complex from an evolutionary perspective.
KeywordsHead Domain Histidine Ligand Geobacter Species Rieske Protein Redox Midpoint Potential
– Cytochrome b;
– Electron Paramagnetic Resonance;
– Ferredoxin NAD(P)H Reductase;
– Last Universal Common Ancestor;
– 2-n-nonyl-4-hydroxylquinoline N-oxide;
– Photosynthetic reaction center;
The authors thank Barbara Schoepp-Cothenet, Wolfgang Nitschke and Daniel Picot for careful reading of the manuscript and helpful discussions. They are grateful to Daniel Picot and David Stroebel for the structure coordinates of the b 6 f complex from Chlamydomonas reinhardtii in the presence of NQNO. Frauke Baymann and Felix ten Brink are supported by a grant from the French ‘Agence nationale de la recherche’ (ANR-10-BLAN-1506).
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