A versatile artificial metalloenzyme scaffold enabling direct bioelectrocatalysis in solution.

Artificial metalloenzymes (ArMs) are commonly designed with protein scaffolds containing buried coordination pockets to achieve substrate specificity and product selectivity for homogeneous reactions. However, their reactivities toward heterogeneous transformations are limited because interfacial electron transfers are hampered by the backbone shells. Here, we introduce bacterial small laccase (SLAC) as a new protein scaffold for constructing ArMs to directly catalyze electrochemical transformations. We use molecular dynamics simulation, x-ray crystallography, spectroscopy, and computation to illustrate the scaffold-directed assembly of an oxo-bridged dicobalt motif on protein surface. The resulting ArM in aqueous phase catalyzes electrochemical water oxidation without mediators or electrode modifications. Mechanistic investigation reveals the role of SLAC scaffold in defining the four-electron transfer pathway from water to oxygen. Furthermore, we demonstrate that SLAC-based ArMs implemented with Ni, Mn, Ru, Pd, or Ir also enable direct bioelectrocatalysis of water electrolysis. Our study provides a versatile and generalizable route to complement heterogeneous repertoire of ArMs for expanded applications.