Mechanistic and Structural insights into the bifunctional enzyme PaaY from Acinetobacter baumannii

PaaY is a thioesterase that enables toxic metabolites to be degraded through the bacterial phenylacetic acid pathway. Thioesterase activity assays demonstrate a preference for Lauroyl-CoA as a substrate. The AbPaaY trimer structure shows unique domain-swapped C-termini, which increases the stability of the enzyme in vitro and decreases its susceptibility to proteolysis in vivo. The domain-swapped C-termini impact thioesterase substrate specificity and enzyme efficacy without affecting carbonic anhydrase activity. AbPaaY knockout reduced the growth of Acinetobacter in media containing phenylacetic acid, decreased biofilm formation, and impaired hydrogen peroxide resistance. Collectively, AbPaaY is a bifunctional enzyme that plays a key role in the metabolism, growth, and stress response mechanisms of Acinetobacter baumannii.