This short repeat is found in multiple copies in bacterial M proteins. The M proteins bind to IgA and are closely associated with virulence. The M protein has been postulated to be a major group A Streptococcal (GAS) virulence factor because of its contribution to the bacterial resistance to opsonophagocytosis [1].

1: M-related protein (Mrp) contributes to group A streptococcal resistance to phagocytosis by human granulocytes. Podbielski A, Schnitzler N, Beyhs P, Boyle MD; Mol Microbiol 1996;19:429-441. PMID:8830235