M protein (Streptococcus)

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

Not to be confused with Protein M.
Gram_pos_anchor
Identifiers
SymbolGram_pos_anchor
PfamPF00746
Pfam clanCL0501
InterProIPR019948
PROSITEPDOC00373

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 pentapeptide LPXTG, 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 pentapeptide 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.
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References
  1. Chanter N, Talbot NC, Newton JR, Hewson D, Verheyen K (June 2000). "Streptococcus equi with truncated M-proteins isolated from outwardly healthy horses". Microbiology. 146 (Pt 6): 1361–9. doi:10.1099/00221287-146-6-1361. PMID 10846214.
  2. Schneewind O, Jones KF, Fischetti VA (June 1990). "Sequence and structural characteristics of the trypsin-resistant T6 surface protein of group A streptococci". J. Bacteriol. 172 (6): 3310–7. PMC 209141. PMID 2188957.
  3. Fischetti VA, Pancholi V, Schneewind O (September 1990). "Conservation of a pentapeptide 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.
  4. "Streptococcal M protein: molecular design and biological behavior". Retrieved 2009-06-21.
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