An ATP "Synthase" Derived from a Single Structural Domain of Bacterial Histidine Kinase

ATP (adenosine triphosphate) is a vital energy source for living organisms, and its biosynthesis and precise concentration regulation often depend on macromolecular machinery composed of protein complexes or complicated multi‐domain proteins. We have identified a single‐domain protein HK853CA derived from bacterial histidine kinases (HK) that can catalyze ATP synthesis efficiently. Here, we explored the reaction mechanism and multiple factors that influence this catalysis through a combination of experimental techniques and molecular simulations. Moreover, we optimized its enzymatic activity and applied it as an ATP replenishment machinery to other ATP‐dependent systems. Our results broaden the understanding of ATP biosynthesis and show that the single CA domain can be applied as a new biomolecular catalyst used for ATP supply.