Acinetobacter baumannii is an opportunistic Gram-negative pathogen that is an important cause of healthcare-associated infections exhibiting high mortality rates. Clinical isolates of multidrug-resistant (MDR) and extremely drug-resistant (XDR) A. baumannii strains are increasingly being observed. Compounding this concern is the dearth of new antibacterial agents in late-stage development that are effective against MDR and XDR A. baumannii. As part of an effort to address these concerns, two genes (aroA and aroC) of the shikimate pathway have previously been determined to be essential for the growth and survival of A. baumannii during host infection (i.e. to be essential in vivo). This study expands upon these results by demonstrating that the A. baumannii aroK gene, encoding shikimate kinase (SK), is also essential in vivo in a rat soft-tissue infection model. The crystal structure of A. baumannii SK in complex with the substrate shikimate and a sulfate ion that mimics the binding interactions expected for the β-phosphate of ATP was then determined to 1.91 Å resolution and the enzyme kinetics were characterized. The flexible shikimate-binding domain and LID region are compared with the analogous regions in other SK crystal structures. The impact of structural differences and sequence divergence between SKs from pathogenic bacteria that may influence antibiotic-development efforts is discussed.
Keywords: Acinetobacter baumannii; antibiotic target; enzyme kinetics; essential gene; ligand-induced conformational change; multi-drug and extreme drug resistance; shikimate kinase.