M protein

M Protein is a major virulence factor of Streptococcus pyogenes, with a role in the pathogenesis of both superficial and invasive diseases. It is a coiled-coil protein that extends from the cell surface of S. pyogenes and is anchored to the cell membrane.

Structure

M protein is a dimeric coiled-coil protein, with each monomer consisting of an alpha-helical chain. The N-terminal region of the protein is highly variable, allowing for antigenic variation, while the C-terminal region is more conserved.

Function

M protein has multiple functions that contribute to the virulence of S. pyogenes. It inhibits phagocytosis by binding to the Fc region of IgG antibodies, preventing opsonization. It also binds to fibrinogen, which can lead to the formation of a protective fibrin shield around the bacterium. Additionally, M protein can bind to various host proteins, including albumin and the complement regulator factor H, further enhancing the survival of S. pyogenes in the host.

Clinical significance

Due to its role in the pathogenesis of S. pyogenes, M protein is a target for vaccine development. However, the high variability of the N-terminal region has made this challenging. Some M protein types are also associated with specific diseases. For example, M1 and M3 types are often associated with invasive diseases, while M12 and M49 types are associated with acute rheumatic fever.

See also

• Streptococcus pyogenes
• Virulence factor
• Phagocytosis
• Opsonization
• Fibrinogen
• Factor H
• Rheumatic fever