The streptococcal M protein: a highly versatile molecule

Interaction of the M-protein of group A Streptococcus (GAS) with its numerous host binding partners might assist the bacteria in evading host immune responses. Although the extensive diversity of this protein has been highlighted by different GAS typing schemes, most of the structural and functional information has been obtained from a limited number of types. Increasing numbers of epidemiological, clinical and biological reports suggest that the structure and function of the M protein is less conserved than previously thought. This review focuses on the known interactions between M proteins and host ligand proteins, emphasizing that our understanding of this well-studied molecule is fragmented.