Degree Name

Doctor of Philosophy


Illawarra Health and Medical Research Institute


In this study 1086 GAS isolates collected from 31 countries representing 175 M-types were phylogenetically assessed on their full length mature M protein sequence, with the aim of developing a new cluster-based classification system which would support future vaccine development and functional studies. Phylogenetic analysis identified that 175 M-types could be grouped in to 2 clades, 2 sub-clades and 48 clusters, 16 of which encompassed 82% of all analysed M-types. To evaluate the utility of this novel classification system as a tool for identification of M protein function, 26 M proteins representing 24 distinct M-types encompassing all major cluster groups were recombinantly expressed and screened for binding against a select range of host proteins. Surface plasmon resonance (SPR) binding experiments identified that both fibrinogen and plasminogen binding function was restricted to clade-Y. Plasminogen binding was further restricted to cluster D4 whereby all M protein contained the highly predictive plasminogen binding motif. High affinity IgA binding was observed only by M proteins associated with emm-clusters E1 and E6 whereas IgG binding was observed by emm-clusters E1, E3, E4, E6, A-C3 and non-clustered M proteins M57 and M14. Complement inhibitor C4-binding protein was shown to only bind clade-X M protein representatives, specifically emm-clusters E1, E3, E4 and E6. Although all M proteins in study were shown to express the previously characterised human serum albumin binding domain, emm-cluster E4 and D4 M protein representatives M53 and M98 were shown not to bind human serum albumin. The ability of GAS vaccine candidate ‘Streptococcal vaccine 1’ (SV1) to effectively opsonise the C-repeat targeted domains of the M proteins in this study was assessed in the presence of IgG, IgA, plasminogen, fibrinogen and albumin. Competitive SPR binding analysis identified that α-SV1 IgG binding did not compete for binding with the respective host proteins. Only IgA binding by E1 M proteins was shown to both inhibit and outcompete α-SV1 IgG binding interactions. These results clearly demonstrate the utility of this GAS classification system based on full length M protein sequence with applications of facilitating future M protein functional studies, epidemiological surveillance and vaccine development.

This study clearly demonstrates the development and utility of the newly implemented GAS classification system. Furthermore, we have identified novel M protein functions which may contribute to the different stages during GAS infection. These results illustrate the homologous genetic and functional properties of distinct M-types in regions where the epidemiology of infection is diverse. A better understanding of M protein interaction with the host will broaden our knowledge of GAS disease progression, facilitating the development of future therapeutics.



Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.