Structural and functional insights into Pseudomonas aeruginosa ApaH, a diadenosine tetraphosphatase crucial for bacterial virulence.

Infections by Pseudomonas aeruginosa are a major cause of severe morbidity and mortality in immunocompromised patients and people with cystic fibrosis, largely due to the pathogen's ability to resist antibiotic treatment and to deploy multiple virulence strategies that promote persistence in the host. We have recently uncovered that the signaling molecule diadenosine tetraphosphate (Ap4A) acts as a crucial regulator of P. aeruginosa virulence. Specifically, deletion of the Ap4A-degrading enzyme, diadenosine tetraphosphatase (ApaH), dramatically reduces the expression of key virulence factors. The structural and molecular properties of P. aeruginosa ApaH (PaApaH) remain uncharacterized. Here, we present an integrated biochemical, structural, computational, and phenotypic characterization of PaApaH. We define the molecular determinants of its manganese-dependent Ap4A hydrolytic mechanism and establish a direct functional link between PaApaH catalytic activity and virulence phenotypes in vivo. Together with the absence of ApaH homologs in eukaryotes, these findings place PaApaH as an attractive and selective target for antivirulence therapeutic strategies against P. aeruginosa infections.