Characterisation of NagA and NagB from methicillin-resistant Staphylococcus aureus.

Abstract

The principal aim of this thesis is to build an understanding of how amino sugars are metabolised in a clinically relevant strain of Staphylococcus aureus. Amino sugars, such as sialic acid and N-acetylglucosamine, are prevalent mucosal sugars that are incorporated into glycoconjugates attached to mucosal cell surfaces. Specifically, the amino sugars can be scavenged from host glycoconjugates and metabolised by bacterial pathogens as a nutrient source. Staphylococcus aureus possesses the enzymatic machinery to scavenge host-derived host-derived amino sugars from their surrounding environment and utilise them as sources, of carbon, nitrogen and cell wall precursors.

A number of amino sugar metabolic pathways converge upon two enzymes, Nacetylglucosamine- 6-phosphate deacetylase, NagA, and glucosamine-6-phosphate deaminase, NagB. These enzymes catalyse the utilisation steps of these pathways, directing metabolites into either peptidoglycan biosynthesis or glycolysis. Due to this central role in the metabolism of host-derived nutrients, understanding of the structure, function and any patterns for regulation of these enzymes will inform the development of new antibiotic and therapeutic strategies.

The structure and function of NagA and NagB from methicillin-resistant S. aureus were investigated in this thesis. This constitutes the first biophysical characterisation of these enzymes from S. aureus. Structural data show that both of these enzymes adopt a dimeric architecture in solution, which is a novel arrangement in the case of NagB. Kinetic analyses detail the catalytic capabilities of both enzymes, and suggest two different patterns of regulation that may influence the activity of these enzymes in vivo.

Overall, these experiments add to the understanding of how amino sugars are utilised by S. aureus, and provide a basis for further research into NagA and NagB structure, function and regulation.