Group A streptococcal immunoglobulin-binding proteins: adhesins, molecular mimicry or sensory proteins?

Pathogenic streptococci express multiple immunoglobulin-binding proteins (IGPs) on their surface that are similar in sequence and structure to the antiphagocytic M proteins. Both are evolutionary products of a duplicated ancestral gene and are components of the Vir gene cluster. Except for M proteins, there is little direct experimental evidence to implicate IGPs in pathogenesis. Several functions of IGPs are postulated and discussed.