Conformational properties of the bis-μ-(thiolato) dicopper center in cytochrome c oxidase

Abstract

The novel bis-μ(thiolato) dicopper center (CuA) forms the electron entry site in the respiratory enzyme, cytochrome c oxidase. While most of the electron transfer copper proteins consist of a mono-nuclear copper center, the presence of a dinuclear copper in cytochrome c oxidase has attracted immense interest. The CuA center from the mesophilic organism, <i style="mso-bidi-font-style:normal">P. denitrificans</i> (PdCuA) and from the thermophilic organism <i style="mso-bidi-font-style:normal">T. thermophilus </i>(TtCuA) have very similar spectroscopic and electronic properties, albeit the stability of the two proteins are significantly different from each other. This dinuclear copper center undergoes interesting conformational change induced by change in the <i>p</i>H of the solution, which involves equilibrium conversion of the purple ‘charge-delocalized’ form to a ‘valance-trapped’ form of the metal center. The <i>p</i>H dependent conformational changes in the PdCuA and TtCuA show different <i>pK</i>_a values indicating involvement of different amino acids in the process. The conformation change near the dinuclear center in the mesophilic protein PdCuA is extremely fast while that in the thermophilic protein TtCuA is very slow. The results of recent studies on the conformational properties of this novel metal center in the protein have been outlined in this mini-review in the light of understanding their implications in biology.