The M-protein consists of two polypeptides arranged in a coiled-coil structure that is held
in the cell membrane (Figure 4). The C-terminal domain is highly conserved, anchored in
the cell membrane via the LPSTGE motif, while the surface-exposed N-terminal portion
is highly variable and is responsible for serotype specificity. M protein is a major surface
antigen and virulence factor, which is encoded by the emm gene. M proteins are involved
in various stages of GAS pathogenesis including adhesion, internalization, immune
evasion and tissue invasion. It confers resistance to phagocytosis and killing by
polymorphonuclear leukocytes by binding to complement control factors and other host
proteins to prevent activation of the alternate complement pathway