Site-site interactions enhances intramolecular electron transfer in Streptomyces coelicolor laccase.

Control of electron transfer rates, caused by intrinsic protein structural properties, is an intriguing feature of internal biological electron transfer (ET) reactions. The small laccase (SLAC) isolated from Streptomyces coelicolor has recently been shown to have structural and reactivity features distinct from those of other laccases. While other copper oxidases contain three cupredoxin domains, the SLAC 3D structure has recently been determined and shown to consist of only two, and a different reaction intermediate has been reported for it. It was therefore of particular interest to investigate the intramolecular ET between the type 1 and the trinuclear copper center in SLAC which is a crucial step in the catalytic cycle of the multicopper oxidases, leading to dioxygen reduction to water. This ET step was found to markedly depend on the reduction state of the enzyme, possibly reflecting site-site interactions so far not observed in other multicopper oxidases.