X-ray structure and the reaction mechanism of bovine heart cytochrome c oxidase

X-ray structure of bovine heart cytochrome c oxidase in the fully oxidized state shows a peroxide bridging between Fe3+ and Cu2+ in the O-2 reduction site. The bond distances for Fe-O and Cu-O are 2.52 and 2.16 Angstrom, respectively. The structure is consistent with antiferromagnetic coupling between the two metals, which has long been known and to recent redox titration results [J. Biol. Chem. 274 (1999) 33403]. The trigonal planer coordination of Cu1+ in the O-2 reduction site is consistent with the very weak interaction between Cu1+ and O-2 bound at Fe2+ revealed by time-resolved resonance Raman investigations. One of the three histidine imidazoles coordinated to the Cu ion in the O-2 reduction site fixes a tyrosine phenol group near the O-2 reduction site with the direct covalent link between the two groups. The structure suggests that the phenol group is the site for donating protons to the bound O-2. Redox-coupled conformational change in an extramembrane loop indicates that an aspartate (Asp51) in the loop apart from the O-2 reduction site is the site for proton pumping. (C) 2000 Elsevier Science B.V. All rights reserved.