The transfer of electrons and protons between membrane-bound respiratory complexes is
facilitated by lipid-soluble redox-active quinone molecules (Q). This work presents a
structural analysis of the quinone-binding site (Q-site) identified in succinate: ubiquinone
oxidoreductase (SQR) from Escherichia coli. SQR, often referred to as Complex II or
succinate dehydrogenase, is a functional member of the Krebs cycle and the aerobic
respiratory chain and couples the oxidation of succinate to fumarate with the reduction of …