Emerging classes of copper enzymes.

Copper-dependent enzymes catalyze some of nature's most challenging oxidative transformations, yet many copper cofactors lack distinctive spectroscopic signatures or are kinetically labile, complicating their discovery and mechanistic characterization. Recent advances in genome mining, heterologous expression, and protein structural prediction have accelerated the identification of previously unrecognized copper enzymes. This Current Opinion highlights two emerging families of binuclear type 2 copper enzymes: plant-specific BURP domain peptide cyclases (BpCs) and fungal DUF3328 dicopper oxidative enzymes (DDOEs). Both families couple dioxygen reduction to oxidative chemistry through conserved dicopper active sites and catalyze oxidative peptide crosslinking; DDOEs additionally perform hydroxylation, halogenation, oxidative biaryl crosslinking, and, putatively, desaturation. By comparing these plant and fungal enzymes, we establish a unified framework for their biological functions, active-site architectures, dioxygen reduction/activation strategies, catalytic mechanisms, and DDOE nomenclature. Together, these enzymes redefine the scope of copper-dependent oxidation and provide new opportunities for biocatalysis, bioengineering, and synthetic biology.