Group A Streptococcus interacts with glycosaminoglycans via M proteins to modulate bacterial adherence in vitro.

Glycosaminoglycans (GAGs) are enriched in the cutaneous extracellular matrix and have important roles in bacterial colonisation. Group A Streptococcus (GAS) can be categorised by emm patterning and M-family protein expression. M proteins of GAS are major adhesins with lectin-binding properties. This study aimed to provide a comprehensive specificity and affinity profile of phylogenetically diverse M proteins to a range of sulfated host GAGs and to investigate the physiological relevance of these interactions. Chondroitin sulfate preferentially associated with M proteins of A-C pattern strains, with binding localised to the central variable region of M1 protein. Dermatan sulfate was shown to associate with M proteins of all pattern type strains, with recognition involving multiple sites on M proteins. Heparin and heparan sulfate exclusively interacted with M proteins of A-C and D pattern strains. Multiple sites of M proteins were involved in heparin recognition, as indicated by surface plasmon resonance and site-directed mutagenesis of the heparin-binding XBXBX motif in the hypervariable-central region of M53 protein. In contrast, binding of heparan sulfate was localised to the non-repeat region between the B2 repeat and C1 repeat of M53 proteins. 5448 (M1-expressing GAS, A-C pattern) was shown to bind chondroitin sulfate, dermatan sulfate and heparin in an M protein-dependent manner. Furthermore, recruitment of chondroitin sulfate or dermatan sulfate by M1 proteins, but not heparin, was shown to increase GAS adherence to human HaCaT keratinocytes. This study increases our understanding of the molecular mechanisms underlying GAS adhesion, with key implications for bacterial colonisation and persistence of infection.