The multicopper oxidase from the archeon Pyrobaculum aerophilum shows nitrous oxide reductase activity

The multicopper oxidase from the hyperthermophilic archaeon Pyrobaculum aerophilum McoP was produced in Escherichia coli and purified to homogeneity. The enzyme consists of a single subunit with 49.6-kDa and the combined results of UV-visible, CD, EPR and resonance Raman showed the typical spectroscopic characteristics of the multicopper oxidases. Analysis of the McoP sequence allowed its structure to be derived by comparative modeling methods. McoP is a hyperthermoactive and thermostable enzyme with an optimum reaction temperature of 85°C, a half-life of inactivation of around 6 h at 80°C, and temperature values at the mid point from 97 to 112°C. McoP is an efficient metallo-oxidase that catalyzes the oxidation of cuprous and ferrous ions with turnover rates of 356 and 128 min-1, respectively, at 40°C. Is is noteworthy that McoP follows a ping-pong mechanism with 3-fold higher catalytic efficiency when using nitrous oxide as electron acceptor than when using dioxygen, the typical oxidizing substrate of multicopper oxidases. This finding led us to propose that McoP represents a novel archaeal nitrous oxide reductase most probably involved in the final step of the denitrification pathway of P. aerophilum.