M protein is a virulence factor that can be produced by certain species of Streptococcus. ^[1]

Viruses, parasites and bacteria are covered in protein and sugar molecules that help them gain entry into a host by counteracting the host's defenses. One such molecule is the M protein produced by certain streptococcal bacteria. At its C-terminus within the cell wall, M proteins embody a motif that is now known to be shared by many Gram-positive bacterial surface proteins. The motif includes a conserved hexapeptide LPXTGE, which precedes a hydrophobic C-terminal membrane spanning domain, which itself precedes a cluster of basic residues at the C-terminus. ^{[2] [3]}

M protein is strongly anti-phagocytic and is the major virulence factor for group A streptococci (Streptococcus pyogenes). It binds to serum factor H, destroying C3-convertase and preventing opsonization by C3b. However plasma B cells can generate antibodies against M protein which will help in opsonization and further the destruction of the microorganism by the macrophages and neutrophils. Cross-reactivity of anti-M protein antibodies with heart muscle has been suggested to be associated in some way with rheumatic fever.

It was originally identified by Rebecca Lancefield, ^[4] who also formulated the Lancefield classification system for streptococcal bacteria. Bacteria like S. pyogenes, which possess M protein are classified in group A of the Lancefield system.

Literature

• Fischetti VA, Pancholi V, Schneewind O (September 1990). "Conservation of a hexapeptide sequence in the anchor region of surface proteins from gram-positive cocci". Mol. Microbiol. 4 (9): 1603–5. doi: 10.1111/j.1365-2958.1990.tb02072.x. PMID  2287281.
• Pierre R. Smeesters; David J. McMillan; Kadaba S. Sriprakash (June 2010). "The streptococcal M protein: a highly versatile molecule". Trends in Microbiology. 18 (6): 275–282. doi: 10.1016/j.tim.2010.02.007. PMID  20347595.

References