Characterisation of cell wall enzymes from Streptococcus pneumoniae

• Main Author: Bui, Nhat Khai
• Published: University of Newcastle Upon Tyne 2009
• Subjects: 579.355
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556139

Murein and its turnover products are recognised by components of the innate immune system leading to an inflammatory response and resulting in the killing of bacteria. To counter the clearance by the innate immune system pathogens like Streptococcus pneumoniae have enzymes to modify their cell wall so that they are no longer recognised. The most common modifications are the N-deacetylation and O-acetylation of the glycan strands in the murein. Deacetylated murein was shown to be a poor substrate for lysozyme which is an important factor of the innate immune system capable of lysing sensitive bacteria that have unmodified murein. The single pneumococcal protein responsible for the deacetylation of murein is the murein N- acetylglucosamine deacetylase A (PgdA). Thus PgdA is a possible target for antibacterial therapy. An economical and ease-to-use assay is required to screen for inhibitors of PgdA. Within this work, such an assay has been established using recombinant PgdA with chromogenic substrates. For the first time the activity of purified PgdA with a natural substrate, murein from S. pneumoniae, has been demonstrated. Another interesting candidate as a possible target for inhibitors is the putative murein hydrolase PcsB. However, there are no biochemical data available yet, and in silico comparison and deletion mutants gave only vague hints for a hypothetical function as murein hydrolase. In this work a recombinant, soluble version of PcsB was purified. It showed no significant enzymatic activity against pneumococcal cell wall or murein.