Background: Tissue injury including extracellular matrix (ECM) degradation is a hallmark of group A Streptococcus (GAS) skin infection. Hyaluronic acid, dermatan sulfate, heparin, heparan sulfate and chondroitin sulfate are glycosaminoglycans (GAGs) that are enriched in the cutaneous ECM and have important roles in bacterial colonisation and wound healing. Some GAS M proteins bind GAGs, but these interactions are not well understood. The current study aimed to determine the specificity and affinity of phylogenetically diverse M proteins to GAGs and provide a novel characterisation of GAS-GAG interactions.
Methods: Initial screening of M protein-GAG binding was achieved using a glycan microarray, and interactions were validated using surface plasmon resonance. Binding of fluorescein-labelled hyaluronic acid and heparin to GAS strains 5448 (emm1) and ALAB49 (emm53) and their respective isogenic M protein deletion mutants was assessed by flow cytometry.
Results: Hyaluronic acid bound all M proteins tested. Heparan sulfate and heparin exclusively interacted with M proteins of A-C and D pattern strains. Chondroitin sulfate A preferentially bound M proteins of A-C pattern strains, while dermatan sulfate bound to M proteins associated with all pattern type strains. Both hyaluronic acid and heparin bound whole GAS in an M protein-dependant manner, however deletion of emm53 from ALAB49 did not reduce the number of cells binding heparin despite an overall decrease in fluorescence, indicating other surface receptors may also bind heparin. Novel hyaluronic acid and heparin binding motifs are proposed.
Conclusions: GAG binding is conserved across GAS M proteins, with evidence of M protein-mediated strain specific interactions.