Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2022

Genetically distinct M-related proteins from Group A Streptococcus and their interactions with human IgG (80832)

Emma-Jayne Proctor 1 2 , Hannah Frost 3 , Sandeep Satapathy 1 2 4 , Gwenaëlle Botquin 3 , Jody Gorman 1 5 , David De Oliveira 6 , Jason McArthur 1 2 , Mark Davies 7 , 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. Illawarra Health and Medical Research Institute, Wollongong, New South Wales, Australia
  6. Australian Infectious Disease Research Centre, School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Queensland, Australia
  7. Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Melbourne, Victoria, Australia

Group A Streptococcus (GAS) is a Gram-positive human pathogen estimated to cause over 500,000 deaths per year. GAS 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 effects the Mrp-IgG interaction. Herein, we report that diverse Mrp exhibit conformational differences, but all bind human IgG subclasses with nanomolar affinity. Circular dichroism revealed that the percent α-helicity varied between Mrp from 61-93%, however this variation was not associated with differences in affinity for human IgG which ranged from 3.7-11.1 nM for mixed IgG. Surface plasmon resonance confirmed Mrp displays preferential IgG-subclass binding. All Mrp were found to have a significantly weaker affinity for IgG3 (p<0.05), compared to all other IgG-subclasses. Plasma pulldown assays analysed via western blot revealed that all Mrp were able to bind IgG in the presence of other serum proteins. Furthermore, we report for the first time that dimeric Mrp binds to IgG with a 1:1 stoichiometry, enhancing our understanding of this important host-pathogen interaction.