Polyphosphate Kinase from , One Enzyme Catalyzing a Two-Step Cascade Reaction to Synthesize ATP from AMP.

This study characterizes a novel polyphosphate kinase from (PPK2-III), an enzyme with potential applications in ATP regeneration processes. Bioinformatic and structural analyses confirmed the presence of conserved motifs characteristic of PPK2 enzymes, including Walker A and B motifs, and the subclass-specific residue E137. Molecular docking simulations showed AMP had the highest binding affinity (-7.0 kcal/mol), followed by ADP (-6.5 kcal/mol), with ATP having the lowest affinity (-6.3 kcal/mol). It was overexpressed in , after purification enzymatic activity assays revealed that PPK2-III needed divalent cations (Mg⁺, Mn⁺, Co⁺) as cofactors to be active. Functional assays revealed its ability to synthesize ATP from AMP through a stepwise phosphorylation mechanism, forming ADP as an intermediate, achieving 70% ATP conversion (TTN 4354.7) after 24 h. Kinetic studies indicated cooperative behavior and substrate preference, with AMP phosphorylation to ADP being the most efficient step. The enzyme demonstrated high thermostability (T = 62 °C) and a broad pH stability range (pH 6.0-9.0), making it suitable for diverse biocatalytic applications. The study highlights PPK2-III as a robust and versatile candidate for cost-effective ATP regeneration, offering advantages in industrial processes requiring stoichiometric amounts of ATP.