Analysis of the display and localisation of surface protein Clumping Factor A of Staphylococcus aureus

Staphylococcus aureus is a major human pathogen responsible for infections of varying severity, globally. It is a major health concern due to the presence of antibiotic-resistant strains such as methicillin-resistant S. aureus (MRSA), a “superbug” which is multidrug resistant. One mechanism by which S. aureus successfully colonises and infects its host is through the production of virulence factors which have roles such as host tissue adherence, toxicity, and immune cell evasion. S. aureus is a Gram-positive bacterium meaning it has a thick outer cell wall primarily made up of peptidoglycan. The cell wall is decorated with an array of surface proteins, including those classified as virulence factors. One major group of virulence factors are cell wall-associated proteins which can be covalently-bound to the cell wall via sortase, an enzyme which catalyses the interaction between the C-terminus of the peptide and peptidoglycan. This study attempted to further understand the mechanisms by which surface proteins come to be displayed on the cell wall of S. aureus, focussing on the secretion of the protein Clumping Factor A (ClfA). ClfA has a conserved motif as part of its N-terminal signal peptide (YSIRK-GXXS) which has previously been shown to interact with lipoteichoic synthesis events which primarily occur at the septum during cell division. My work employed a combination of bioinformatic analysis, genetic manipulation techniques, and microscopy approaches to understand the mechanisms behind ClfA secretion and visualise the location of ClfA display with respect to the YSIRK-GXXS motif and cell wall division machinery. As well as monitoring secretion in wild-type S. aureus, how protein secretion is affected by methicillin-treatment in MRSA was investigated. This revealed antibiotic treatment of MRSA to alter ClfA display. My work contributes to the understanding of surface protein display and how this may be useful in elucidating important mechanisms of host-pathogen interaction.