Oral Presentation BACPATH 2022

Structural biology approaches provide insights into the novel interaction between the M-related proteins from Streptococcus pyogenes and plasma proteins   (#18)

Emma-Jayne Proctor 1 2 , Bhanu Mantri 2 , Hannah Frost 3 , Gwenaëlle Botquin 3 , Jody Gorman 1 2 , David De Oliveira 4 , Jason McArthur 1 2 , Mark Davies 5 , Gökhan Tolun 2 , Anne Botteaux 3 , Pierre Smeesters 3 , 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. Molecular Bacteriology Laboratory, Universit ´e Libre de Bruxelles, Brussels, Belgium
  4. Australian Infectious Disease Research Centre, School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland, Australia
  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) M-related proteins (Mrp) are predicted dimeric α-helical-coiled-coil fibrillar cell membrane bound surface proteins. During infection, Mrp recruit human Immunoglobulin G (IgG) and Fibrinogen (Fg) to the bacterial surface, conferring enhanced phagocytosis resistance and augmented growth in human blood. However, Mrp show a high degree of sequence diversity. It is currently not known whether this diversity effects protein structure, or the host-pathogen interactions mediated by Mrp. Additionally, the ability of Mrp to interact with other plasma proteins is uncharacterised. Herein, nine representative Mrp sequences were selected from a global GAS database for molecular characterisation to establish the effect of Mrp diversity on protein structure and function.  Examination of Mrp using circular dichroism, mass photometry and negative staining transmission electron microscopy confirmed that Mrp exist as dimeric, α-helical, fibrillar proteins. Surface Plasmon Resonance (SPR) was performed to evaluate the affinity of each Mrp for Fg, Plasminogen (Plg), and all four IgG subclasses. All Mrp studied bound to Fg via Fragment D (FgD), and all IgG subclasses with nanomolar affinity. Mrp also showed preferential subclass binding to IgG1, IgG2, and IgG4, and a significantly lower affinity for IgG3. Conversely, only three of the nine Mrp were found to interact with Plg. However, Plg binding by Mrp was significantly enhanced following pre-incubation with Fg, showing for the first time that Mrp provides an alternative mechanism for Plg recruitment to the bacterial cell surface. Acquisition of Plg at the GAS cell surface have been previously implicated in tissue destruction and overstimulation of the human inflammatory response during infection. Combined, these data demonstrate that the Mrp plays an important role in GAS host-pathogen interactions. Mrp-IgG and Mrp-Fg interactions are conserved amongst phylogenetically and structurally diverse Mrps, suggesting that these are an important host-pathogen interaction in GAS virulence and potential therapeutic target.