Inhibitory studies of Neisseria meningitidis and Campylobacter jejuni N-acetylneuraminic acid synthase

N-Acetylneuraminic acid synthase (NANAS) is an enzyme responsible for the biosynthesis of N-acetylneuraminic acid (NANA). NANA is the most common form of a group of nine carbon sugar molecules called the sialic acids. NANA production is common in mammalian cells for vital physiological processes. A few species of microorganisms, including pathogenic bacteria such as Neisseria meningitidis and Campylobacter jejuni, are known to synthesise NANA by their bacterial NANAS. These pathogenic bacteria synthesise NANA for molecular mimicry, allowing them to evade the host immune system. This thesis examines the NANAS enzymes from N. meningitidis and C. jejuni. Inhibitory studies with these enzymes were explored by performing enzyme kinetics with substrate analogues and a product analogue which structurally mimic the natural substrates or product of NANAS. Inhibition constants were determined for a variety of analogues to give insight in to how the enzyme accommodates its substrates within the active site of NANAS. This study may be a useful step in the development of alternative antibiotics for bacterial meningitis and other diseases in the future. NANAS catalyses a condensation reaction between phosphoenolpyruvate (PEP) and N-acetyl mannosamine (ManNAc). Both PEP and ManNAc analogues were explored as inhibitors of the enzymes. Results from this study show that increasing steric bulk of the substituents at C3 of PEP unexpectedly delivers more potent inhibition of the enzyme. This finding suggests that a slightly modified binding position of the PEP analogue within the PEP binding site of the enzyme may be responsible for the inhibition. A reduced acyclic analogue of ManNAc was found to be an effective inhibitor of the enzymes. This finding indicates how important the acyclic form of ManNAc is in the reaction mechanism catalysed by this enzyme