Laccases: Complex architectures for one-electron oxidations

Laccase (p-diphenol:dioxygen oxidoreductase), one of the earliest discovered enzymes, contains four copper ions in two active sites and catalyzes a one-electron oxidation of substrates such as phenols and their derivatives, or aromatic amines, coupled to a four-electron reduction of dioxygen to water. The catalytic mechanism has been studied for decades but is still not completely elucidated, especially in terms of the reduction of dioxygen to water. The key structural features of this enzyme are under investigation in several groups using techniques such as X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy, and site-directed mutagenesis. The high interest in laccases is explained by the large number of biotechnological applications. In this review, the most recent research on the overall structural features as well as on the structures and properties of the active sites are summarized, along with currently proposed mechanisms of reaction.