Tetranuclear Copper Cluster of N2O Reductase: A Distinctive Copper-Sulfur Metallocluster

Copper is an essential element involved in several cofactors and organometallic compounds used as catalysts. Although most biological copper centers contain one to three copper ions, nature has evolved a unique tetranuclear copper-sulfur cluster that has attracted the attention of both biochemists and inorganic chemists. This multinuclear copper center has only been observed in one enzyme, nitrous oxide reductase, which catalyzes the reduction of nitrous oxide to dinitrogen, the final step of the denitrification pathway. The structural, spectroscopic, and kinetic properties of this [4CuS] cluster have been the subject of extensive investigation, revealing that it exists in two distinct forms within the enzyme, CuZ[4Cu:2S] and CuZ*[4Cu:1S], with different oxidation states, spectroscopic signatures, and catalytic properties. These features are discussed together with recent advances in understanding the biosynthesis and assembly of this cluster. Inorganic chemists have synthesized a variety of structural and functional models of the CuZ cluster, although none fully reproduces the electronic structure and catalytic efficiency of the native active center. This review discusses the interplay between biological and synthetic studies, illustrating how advances in one field continue to inspire progress in the other while identifying the challenges that must be overcome to achieve truly functional biomimetic catalysts.