E-Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2021

Characterising the role of the M-related protein from Group A Streptococcus in virulence (#331)

Emma-Jayne Proctor 1 2 , Sandeep Satapathy 1 2 3 , Bhanu Mantri 1 2 , Hannah Frost 4 , Jody Gorman 1 2 , Mark Davies 5 , Gokhan Tolun 1 2 , Anne Botteaux 4 , Pierre Smeesters 4 , Martina Sanderson-Smith 1 2
  1. Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia
  2. School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales, Australia
  3. Department of Cell Biology at Blavatnik Institute, Harvard Medical School, Boston, Massachusetts, United States
  4. Molecular Bacteriology Laboratory, Universit ´e Libre de Bruxelles, Brussels, Belgium
  5. Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Melbourne, Victoria, Australia

Group A Streptococcus (GAS; Streptococcus pyogenes) is a Gram-positive human pathogen responsible for a range of clinical manifestations from superficial infections, to severe invasive diseases and post-infection sequelae. Combined, these conditions are estimated to cause over 500,000 deaths per year. Despite considerable efforts towards vaccine development, there remains no viable vaccine against GAS. The M-related protein (Mrp) is a GAS surface protein identified as a potential vaccine candidate. The recruitment of the plasma protein fibrinogen (Fg) has  been shown to aid in colonisation, persistence and immune evasion of GAS within the host. Mrp has previously been validated as a major GAS Fg-binding protein, an interaction which is essential for the growth of some GAS strains in human blood. However, the molecular mechanisms of the Mrp-Fg interaction have not been characterised in depth. This study aimed to characterise the interaction between Mrp and Fg, among a range of phylogenetically distinct isolates. It has been shown that Mrp contains two Fg binding domains (FBD1 and FBD2). Protein sequence analysis determined that FBD2 is present in all Mrp sequenced to date, whereas FBD1 is not. Surface plasmon resonance (SPR) was utilised to characterise the affinity of nine phylogenetically diverse Mrp to Fg. All Mrp bound Fg with high affinity, via the fragment D domain. The presence of the additional FBD (FBD1) does not enhance Fg binding capacity relative to Mrp with FBD2 only. Moreover, plasma pulldown assays showed all Mrp were able to acquire Fg from plasma, suggesting that the second FBD provides no advantage in a competitive environment. This work provides a detailed characterisation of the interaction between Mrp, a GAS surface protein and promising vaccine candidate, and the human plasma protein Fg. This interaction is likely an important facet of the host-pathogen relationship, particularly in the context of invasive infections, such as bacteraemia. Understanding the role of Mrp in pathogenesis is crucial in evaluating its potential as a GAS vaccine candidate.