Poster Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

The role of PxxP domains of SIC in protecting Streptococcus from antimicrobial peptides (#179)

Miranda E. Vidgen 1 , Johnny X. Huang 2 , Matthew A. Cooper 2 , David J. McMillan 1
  1. Inflammation and Healing Research Cluster, School of Health and Sport Sciences, University of the Sunshine Coast, Maroochydore, QLD, Australia
  2. Institute of Molecular BioScience, The University of Queensland, St Lucia, QLD, Australia

Antimicrobial peptides (AMPs) are part of the innate immune system. They have been identified as a potential new class of therapeutic agents for infection control. However, a small group of pathogenic bacteria have mechanisms to avoid these AMPs. An important factor of the development of AMP based therapeutic strategies will be the characterisation of AMP resistance mechanisms in these bacteria.

Streptococcus pyogenes and S. dysgalactiae subsp. equisimilis are bacteria that colonises the throat and skin of humans, and are the cause of significant human mortality and morbidity. Some strains of these two species avoid AMP activity through the production of extra-cellular SIC-group proteins. It has been suggested that PxxP domains in the proline-rich C-terminal region of these proteins influence AMP binding capacity, facilitating inhibition of AMP action on the bacterial cell.

To test this hypothesis a panel of recombinant SIC-group proteins were produced. These proteins contained point-mutations within the PxxP motifs. Using surface plasmon resonance (SPR) the binding affinity of the modified SIC-group proteins and AMP from the cathelicidin group, LL-37, was assessed. The biological relevance of the observed binding interactions was then examined using a bacterial survival assay, in which the influence of SIC-group protein’s presence on survival was quantified.

The increasing threat of multi-drug resistant bacteria brings new urgency to our search for alternative therapeutic agents for infection control. Using label free binding assays with SPR together with survival assays provide insights into the influence of the proline-rich motifs in the action of AMPs on Streptococcus and resultant resistant mechanisms.