A Novel Protein-Protein Interaction Assay Based on the Functional Complementation of Mutant Firefly Luciferases: Split Structure Versus Divided Reaction

Protein-fragment complementation assays (PCAs) are commonly used to assay protein–pro- tein interaction (PPI). While PCAs based on firefly luciferase (Fluc) in cells or lysates are a user-friendly method giving a high signal/background (S/B) ratio, they are difficult to use in vitro owing to the instability of split Fluc fragments. As a solution to this issue, we devel oped a novel protein–protein interaction assay named FlimPIA using two mutant Flucs, each of which catalyzes one of the two half-reactions catalyzed by the wild-type enzyme. Upon approximation by the tethered protein pairs, the two mutants yielded higher signal owing to a more efficient transfer of the reaction intermediate luciferyl adenylate. FlimPIA showed many advantages over in vitro split Fluc assays, such as longer detectable distance, more sta - ble probes, and higher signal readout in a shorter time period, and it also worked in cellulo.