Antibiotic resistance is a worldwide threat to human health yet fewer new antibiotics are being approved. New antimicrobial drugs are urgently required. 3 Deoxy-D-manno-2-octulosonate-8-phosphate synthase (KDO8PS) is a target for antimicrobial drug design. KDO8PS catalyzes the condensation of D-arabinose-5 phosphate (A5P) with phosphoenolpyruvate (PEP) to produce KDO8P. KDO8PS catalyzes the first committed step in the lipopolysaccharides (LPS) biosynthesis pathway in Gram-negative bacteria and is critical for bacterial pathogenicity/virulence. We have characterized KDO8PS from Campylobacter jejuni (cjKDO8PS), a new metal-dependent KDO8P synthase (KDO8PS). cjKDO8PS is a tetramer in solution and optimally active at pH 7.5 and 60 °C. We have kinetically established that cjKDO8PS follows a rapid equilibrium sequential ordered ter ter kinetic mechanism, where Mn2+ binds first, followed by PEP, then A5P. Pi dissociates first, before KDO8P, then Mn2+. cjKDO8PS was inhibited by KDO8P oxime, a novel slow tight-binding inhibitor. KDO8P oxime is a competitive inhibitor with respect to PEP and A5P, but uncompetitive with respect to Mn2+, with Ki = 10 ± 1 μM and an ultimate Ki* = 0.28 ± 0.10 μM. KDO8P oxime has a residence time (tR) of 5 days on the enzyme, a parameter that is highly correlated to in vivo efficacy. Crystallization conditions for the cjKDO8PS‧Mn2+‧KDO8P oxime complex have been found and can be optimized to obtain a crystal structure that shows how KDO8P oxime interacts with the active sites. / Thesis / Doctor of Science (PhD) / The relentless increase in global antibiotic resistance is, regrettably, not matched with an increase in new effective antibiotics. New antimicrobial drug discovery strategies are desperately needed. Enzymes are key targets for drug design because they catalyze the majority of biological processes. In this project we sought to study and inhibit the activity of KDO8P synthase (KDO8PS) from Campylobacter jejuni, a common cause of food poisoning. KDO8P synthase is a critical enzyme involved in the lipopolysaccharide (LPS) biosynthesis in Gram-negative bacteria. The LPS acts as a permeability barrier and is crucial for bacterial pathogenicity/virulence. We found that C. jejuni KDO8PS is potently inhibited by KDO8P oxime, a novel inhibitor of KDO8PS. This inhibitor presents a unique opportunity to study these enzymes and a platform from which antibiotics against Gram-negative bacteria can be developed.