Bovine cytochrome c oxidase structures enable O ₂ reduction with minimization of reactive oxygens and provide a proton-pumping gate

Abstract

The O 2 reduction site of cytochrome c oxidase (CcO), comprising iron (Fe a 3 ) and copper (Cu B ) ions, is probed by x-ray structural analyses of CO, NO, and CN - derivatives to investigate the mechanism of the complete reduction of O 2 . Formation of the derivative contributes to the trigonal planar coordination of and displaces one of its three coordinated imidazole groups while a water molecule becomes hydrogen bonded to both the CN - ligand and the hydroxyl group of Tyr244. When O 2 is bound to , it is negatively polarized ( ), and expected to induce the same structural change induced by CN - . This structural change allows to receive three electron equivalents nonsequentially from , , and Tyr-OH, providing complete reduction of O 2 with minimization of production of active oxygen species. The proton-pumping pathway of bovine CcO comprises a hydrogen-bond network and a water channel which extend to the positive and negative side surfaces, respectively. Protons transferred through the water channel are pumped through the hydrogen-bond network electrostatically with positive charge created at the Fe a center by electron donation to the O 2 reduction site. Binding of CO or NO to induces significant narrowing of a section of the water channel near the hydrogen-bond network junction, which prevents access of water molecules to the network. In a similar manner, O 2 binding to is expected to prevent access of water molecules to the hydrogen-bond network. This blocks proton back-leak from the network and provides an efficient gate for proton-pumping.

X-ray structure of cyanide-bound bovine heart cytochromecoxidase in the fully oxidized state at 2.0 Å resolution

“…In this study, we determined the structure of the CN À -bound fully oxidized form at 2.0 Å resolution. It should be noted that the X-ray structure of CN À -bound mammalian CcO in the fully reduced state, which was distinctively different from the fully oxidized mammalian CcO in the structure around the haem a 3 -Cu B , including Tyr244, has previously been reported (Muramoto et al, 2010), but to date the structure of the CN À -bound fully oxidized state has not been reported. Comparison of this structure with that of the fully oxidized enzyme previously determined revealed that X-ray irradiation, which induces the accumulation of water in the vicinity of Tyr244, does not induce any significant change in the protein structure.…”

Crystallographic and online spectral evidence for role of conformational change and conserved water in cytochrome oxidase proton pump

“…The results are consistent with the maintenance of the oxidized protein conformation (36), even though the metal centers are reduced, before annealing at warmer temperature allows the protein to change its structure. The strained configuration shows an interesting spectral feature at 589 nm, also observed in the bovine and thermus CcO irradiated crystals (34,37). Other spectral methods such as single-crystal low-temperature EPR or resonance Raman will be needed to determine the nature of this form; the Soret region of the spectrum, which could provide some clues, absorbs too strongly to be measured (Fig.…”

Bioinspired copper catalyst effective for both reduction and evolution of oxygen

“…The typical examples are cytochrome c oxidase and laccase, their active sites contain the similar metal clusters of assembled Cu 2 þ complexes 19,20 . Previous work showed that laccase in vitro is more desirable as the quasichampion potential (onset at 1.2 V versus reversible hydrogen electrode (RHE), pH ¼ 4) is observed on its modified electrode 21 , suggesting that Cu 2 þ ion is supposed to be an ideal catalytic site as long as the energy level of the d-electrons is tuned to a reasonable state.…”