Sequential reconstitution of copper sites in the multicopper oxidase CueO

CueO belongs to the family of multicopper oxidases which are characterized by the presence of multiple copper-binding sites with different structural and functional properties. These enzymes share the ability to couple the one-electron oxidation of substrate to reduction of oxygen to water by way of a functional unit composed of a mononuclear type 1 blue copper site, which is the entry site for electrons, and of a trinuclear copper cluster formed by type 2 and binuclear type 3 sites, where oxygen binding and reduction take place. The mechanism of copper incorporation in CueO has been investigated by optical and EPR spectroscopy. The results indicate unambiguously that the process is sequential, with type 1 copper being the first to be reconstituted, followed by type 2 and type 3 sites.