Discovery and characterization of a nickel enzyme family that catalyses intermolecular hydride shuttling

Nickel-dependent enzymes catalyse incredible transformations. However, few have been discovered so far, limiting our understanding of the role of nickel in nature. Here we develop a bioinformatic pipeline to discover a family of nickel pincer mononucleotide (NPMN)-dependent enzymes with structures that are completely distinct from previously reported NPMN-dependent enzymes. We characterize one family member, NPMN-dependent hydride transferase (NphT), and find that it catalyses intermolecular hydride transfer, which we elucidate through its promiscuous disproportionation of sugars. We solve a 1.3-Å resolution crystal structure of NphT bound to NPMN and interrogate its mechanism through mutagenesis. We discover that NphT is one of many unexplored nickel enzymes within the large aldo-keto reductase superfamily, which catalyses reactions on a wide range of molecules, including secondary metabolites, sugars and drugs. This work reveals a unique enzymatic scaffold that can harness nickel, expands the known NPMN-catalysed transformations to intermolecular hydride transfer and establishes a pipeline for the discovery of distinct families of nickel-dependent enzymes.