LAUSR

A vast array of metal cofactors are associated with the active sites of metalloenzymes. This Opinion describes the most recently discovered metal cofactor, a nickel-pincer nucleotide (NPN) coenzyme that is covalently tethered to lactate racemase from Lactobacillus plantarum. The enzymatic function of the NPN cofactor and its pathway for biosynthesis are reviewed. Furthermore, insights are summarized from recent advances involving other selected organometallic and inorganic-cluster cofactors including the lanthanide-pyrroloquinoline quinone found in certain alcohol dehydrogenases, tungsten-pyranopterins or molybdenum-pyranopterins in chosen enzymes, the iron-guanylylpyridinol cofactor of [Fe] hydrogenase, the nickel-tetrapyrrole coenzyme F430 of methyl coenzyme M reductase, the vanadium-iron cofactor of nitrogenase, redox-dependent rearrangements of the nickel-iron-sulfur C-cluster in carbon monoxide dehydrogenase, and light-dependent changes in the multi-manganese cluster of the oxygen-evolving complex.