NMR study of the exchange coupling in the trinuclear cluster of the multicopper oxidase Fet3p

Fet3p from Saccharomyces cerevisiae is a multicopper oxidase (MCO) which oxidizes Fe²⁺ to Fe³⁺. The electronic structure of the different copper centers in this family of enzymes has been extensively studied and discussed for years with a particular focus on the exchange coupling regime in the trinuclear cluster (TNC). Using NMR spectroscopy we have quantified the exchange coupling constant in the type 3 center in a fully metalated oxidase; this value in Fet3p is significantly higher than that reported for proteins containing isolated type 3 centers as tyrosinase. We also provide evidence of exchange coupling between the type 2 and the type 3 Cu²⁺ ions, which supports the crystallographic evidence of dioxygen binding to the TNC. This work provides the foundation for the application of NMR to these complex systems.