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Acinetobacter baumanniiis 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. baumanniistrains are increasingly being observed. Compounding this concern is the dearth of new antibacterial agents in late-stage development that are effective against MDR and XDRA. baumannii. As part of an effort to address these concerns, two genes (aroAandaroC) of the shikimate pathway have previously been determined to be essential for the growth and survival ofA. baumanniiduring host infection (i.e.to be essentialin vivo). This study expands upon these results by demonstrating that theA. baumannii aroKgene, encoding shikimate kinase (SK), is also essentialin vivoin a rat soft-tissue infection model. The crystal structure ofA. baumanniiSK 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.

Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage, to confirm a multi-track radiation-damage process and to develop a model of that process., Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage. Online UV–visible spectroscopy showed that upon X-irradiation, disulfide radicalization appeared to saturate at an absorbed dose of approximately 0.5–0.8 MGy, in contrast to the saturating dose of ∼0.2 MGy observed using EPR at much lower dose rates. The observations suggest that a multi-track model involving product formation owing to the interaction of two separate tracks is a valid model for radiation damage in protein crystals. The saturation levels are remarkably consistent given the widely different experimental parameters and the range of total absorbed doses studied. The results indicate that even at the lowest doses used for structural investigations disulfide bonds are already radicalized. Multi-track considerations offer the first step in a comprehensive model of radiation damage that could potentially lead to a combined computational and experimental approach to identifying when damage is likely to be present, to quantitate it and to provide the ability to recover the native unperturbed structure.

The enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase catalyzes the sixth step of the seven-step shikimate pathway. Chorismate, the product of the pathway, is a precursor for the biosynthesis of aromatic amino acids, siderophores and metabolites such as folate, ubiquinone and vitamin K. The shikimate pathway is present in bacteria, fungi, algae, plants and apicomplexan parasites, but is absent in humans. The EPSP synthase enzyme produces 5-enolpyruvylshikimate 3-phosphate and phosphate from phosphoenolpyruvate and shikimate 3-phosphateviaa transferase reaction, and is the target of the herbicide glyphosate. TheAcinetobacter baumanniigene encoding EPSP synthase,aroA, has previously been demonstrated to be essential during host infection for the growth and survival of this clinically important drug-resistant ESKAPE pathogen. Prephenate dehydrogenase is also encoded by the bifunctionalA. baumannii aroAgene, but its activity is dependent upon EPSP synthase since it operates downstream of the shikimate pathway. As part of an effort to evaluate new antimicrobial targets, recombinantA. baumanniiEPSP (AbEPSP) synthase, comprising residues Ala301–Gln756 of thearoAgene product, was overexpressed inEscherichia coli, purified and crystallized. The crystal structure, determined to 2.37 Å resolution, is described in the context of a potential antimicrobial target and in comparison to EPSP synthases that are resistant or sensitive to the herbicide glyphosate.