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

Abstract

X-ray structure of bovine heart cytochrome c oxidase in the fully oxidized state shows a peroxide bridging between Fe 3+ and Cu 2+ in the O 2 reduction site. The bond distances for Fe–O and Cu–O are 2.52 and 2.16 Å, 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 Cu 1+ in the O 2 reduction site is consistent with the very weak interaction between Cu 1+ and O 2 bound at Fe 2+ 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.