Streptomyces coelicolor oxidase (SCO2837p): a new free radical metalloenzyme secreted by Streptomyces coelicolor A3(2)

The SCO2837 open-reading frame is located within the conserved central core region of the Streptomyces coelicolor A3(2) genome, which contains genes required for essential cellular functions. SCO2837 protein (SCO2837p) expressed by Pichia pastoris is a copper metalloenzyme, catalyzing the oxidation of simple alcohols to aldehydes and reduction of dioxygen to hydrogen peroxide. Distinct optical absorption spectra are observed for oxidized and one-electron reduced holoenzyme, and a free radical EPR signal is present in the oxidized apoprotein, characteristic of the Tyr-Cys redox cofactor previously reported for fungal secretory radical copper oxidases, galactose oxidase and glyoxal oxidase, with which it shares weak sequence similarity. SCO2837p was detected in the growth medium of both S. coelicolor and a recombinant expression host (Streptomyces lividans TK64) by Western blotting, with the expression level dependent on the nature of the carbon source. This represents the first characterized example of a prokaryotic radical copper oxidase.