Immunoglobulin-binding FcrA and Enn proteins and M proteins of group A streptococci evolved independently from a common ancestral protein.

Significant sequence homology between M proteins and immunoglobulin (Ig)-binding proteins of group A streptococci suggests that these proteins arose by gene duplication followed by the development of functional diversity due to mutations and intragenic recombinations. The deduced sequence of multiple Ig-binding proteins and M proteins were compared to distinguish between two evolutionary models. Did these functionally distinct genes originate in the distant past from duplication of a common ancestral gene and then functionally evolve independently or did they evolve more recently, one from the other by duplication of a fixed gene? Multiple alignments of conserved sequences of these proteins are consistent with the former hypothesis. Comparison of N termini of Ig-binding proteins revealed less diversity than that of the M proteins' N termini, suggesting that these proteins are under less selective pressure to change.