Structural and binding studies of phosphopantetheine adenylyl transferase from Acinetobacter baumannii.

Phosphopantetheine adenylyltransferase (PPAT, EC. 2.7.7.3) catalyzes an essential step in the reaction that transfers an adenylyl group from adenosine tri phosphate (ATP) to 4′-phosphopantetheine (pPant) yielding 3′- dephospho-coenzyme A (dPCoA) and pyrophosphate (PP) in the coenzyme A (CoA) biosynthesis pathway. The enzyme PPAT from Acinetobacter baumannii (Ab PPAT) was cloned, expressed and purified. The binding studies of Ab PPAT were carried out with two compounds, tri‑sodium citrate (TSC) and l -ascorbic acid (LAA, vitamin-C) using fluorescence spectroscopic (FS) and surface Plasmon resonance (SPR) methods. Both methods provided similar values of dissociation constants for TSC and LAA which were of the order of 10−8 M and 10−5 M respectively. The computer aided docking studies indicated fewer interactions of LAA with Ab PPAT as compared to those of TSC. The freshly purified samples of Ab PPAT were crystallized. The crystals of Ab PPAT were soaked in the solutions containing TSC and LAA. However, the crystals of the complex of Ab PPAT with LAA did not diffract well and hence the structure of the complex of Ab PPAT with LAA could not be determined. On the other hand, the crystals of the complex of Ab PPAT with TSC diffracted well and the structure was determined at 1.76 Å resolution. It showed that TSC bound to Ab PPAT at the ATP binding site and formed several intermolecular contacts including 12 hydrogen bonds. The results of binding studies for both TSC and LAA and the structure of the complex of Ab PPAT with TSC clearly indicated a potential role of TSC and LAA as antibacterial agents. • Ascorbic acid and Citric acid bind to Ab PPAT with high affinities. • Structure of Ab PPAT with citric acid was determined at 1.76 Å resolution. • Structure of Ab PPAT with citric acid shows that it binds at substrate binding site. • Both compounds show antibacterial effects against sensitive and resistant isolate. [ABSTRACT FROM AUTHOR]