M protein of Streptococcus pyogenes (M protein)

The M protein of Streptococcus pyogenes is a surface-exposed, coiled-coil virulence protein that forms a dense fibrillar layer on the bacterial surface. It is anchored to the cell wall via a conserved LPXTG motif and sortase-mediated mechanism. The N-terminal region is highly variable among strains and determines serotype (e.g., M1, M3, etc.), while the C-terminal contains conserved anchoring motifs. It mediates immune evasion by blocking complement deposition, interfering with antibody binding (notably IgG Fc domains), binding host plasma proteins (e.g., factor H, fibrinogen, plasminogen), and promoting adhesion and inflammatory responses, enabling pharyngeal and invasive infections. M protein is the major target of the protective immune response, the principal antigen of Lancefield group A classification, and a key focus for multivalent vaccine strategies. However, its molecular mimicry of human tissue proteins underlies the pathogenesis of post-streptococcal autoimmune diseases, notably rheumatic fever.

Other names

Streptococcal M proteinGroup A Streptococcus M proteinGAS M proteinM1 protein

Vaccines: Induce production of protective antibodies that block the protein’s functions, enhance opsonization, and neutralize infection. Antibodies: Promote opsonization for immune clearance by macrophages and neutrophils, neutralize its immune evasion properties.