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 (I g)-binding proteins of group A streptococci suggests that these protei ns 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 functionall y distinct genes originate in the distant past from duplication of a c ommon ancestral gene and then functionally evolve independently or did they evolve more recently, one from the other by duplication of a fix ed 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 protein s' N termini, suggesting that these proteins are under less selective pressure to change.