Copper-dependent halogenase catalyses unactivated C-H bond functionalization

Carbon-hydrogen (C-H) bonds are the foundation of essentially every organic molecule, making them an ideal place to do chemical synthesis. The key challenge is achieving selectivity for one particular C(sp³)-H bond^1-3. In recent years, metalloenzymes have been found to perform C(sp³)-H bond functionalization^4,5. Despite substantial progresses in the past two decades^6,7, enzymatic halogenation and pseudohalogenation of unactivated C(sp³)-H-providing a functional handle for further modification-have been achieved with only non-haem iron/α-ketoglutarate-dependent halogenases, and are therefore limited by the chemistry possible with these enzymes⁸. Here we report the discovery and characterization of a previously unknown halogenase ApnU, part of a protein family containing domain of unknown function 3328 (DUF3328). ApnU uses copper in its active site to catalyse iterative chlorinations on multiple unactivated C(sp³)-H bonds. By taking advantage of the softer copper centre, we demonstrate that ApnU can catalyse unprecedented enzymatic C(sp³)-H bond functionalization such as iodination and thiocyanation. Using biochemical characterization and proteomics analysis, we identified the functional oligomeric state of ApnU as a covalently linked homodimer, which contains three essential pairs-one interchain and two intrachain-of disulfide bonds. The metal-coordination active site in ApnU consists of binuclear type II copper centres, as revealed by electron paramagnetic resonance spectroscopy. This discovery expands the enzymatic capability of C(sp³)-H halogenases and provides a foundational understanding of this family of binuclear copper-dependent oxidative enzymes.