Insights from the structure of the yeast cytochrome bc1 complex: crystallization of membrane proteins with antibody fragments

The ubiquinol:cytochrome c oxidoreductase (EC 1.20.2.2, QCR or cytochrome bc1 complex) is a component of respiratory and photosynthetic electron transfer chains in mitochondria and bacteria. The complex transfers electrons from quinol to cytochrome c. Electron transfer is coupled to proton translocation across the lipid bilayer, thereby generating an electrochemical proton gradient, which conserves the free energy of the redox reaction. The yeast complex was crystallized with antibody Fv fragments, a promising technique to obtain well-ordered crystals from membrane proteins. The high-resolution structure of the yeast protein reveals details of the catalytic sites of the complex, which are important for electron and proton transfer.