Virtual Poster 21st Lancefield International Symposium for Streptococci and Streptococcal Diseases 2022

Molecular characterisation of the interaction between human IgG and M-related proteins from Streptococcus pyogenes. (#206)

Emma-Jayne Proctor 1 2 , Hannah Frost 3 , Sandeep Satapathy 1 2 4 , Gwenaëlle Botquin 3 , Jody Gorman 1 2 , David De Oliveira 5 , Jason McArthur 1 2 , Mark Davies 6 , Anne 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. Department of Cell Biology at Blavatnik Institute, Harvard Medical School, Boston, Massachusetts, United States
  5. Australian Infectious Disease Research Centre, School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland, Australia
  6. Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Melbourne, Victoria, Australia

Background:

Streptococcus pyogenes M-related proteins (Mrp) are dimeric α-helical-coiled-coil cell membrane bound surface proteins. During infection, Mrp recruit human IgG-Fc via their A-repeat regions to the bacterial surface, conferring enhanced phagocytosis resistance and augmented growth in human blood. However, Mrp show a high degree of sequence diversity, and it is currently not known whether this diversity impacts the Mrp-IgG interaction.

Methods:

Herein, nine representative Mrp sequences were selected from a global Streptococcus pyogenes database for molecular characterisation to establish the effect of Mrp diversity on IgG binding. Surface Plasmon Resonance (SPR) was performed to evaluate the affinity of each Mrp for various IgG sub-types. Plasma pulldown assays analysed via western blot were utilised to determine if the diverse Mrp preserve the ability to bind IgG in human plasma. Mass photometry was used to report the binding stoichiometry for Mrp-IgG.

Results:

All nine diverse Mrp maintained binding to all IgG subclasses with nanomolar affinity, despite the observed variation in their secondary structure. Mrp also showed preferential subclass binding to IgG1, IgG2, and IgG4, and a significantly lower affinity for IgG3. Furthermore, in the presence of other serum proteins, the Mrp-IgG interaction was maintained, and the interaction between dimeric Mrp and IgG was found to exist at a 1:1 stoichiometry.

Conclusions:

Taken together, these data demonstrate that the Mrp-IgG interaction is conserved amongst phylogenetically and structurally diverse Mrp, suggesting that the Mrp-IgG interaction is an important host-pathogen interaction in Streptococcus pyogenes virulence.