Expression of the Arp protein, a member of the M protein family, is not sufficient to inhibit phagocytosis of Streptococcus pyogenes.

Many Streptococcus pyogenes immunoglobulin-binding proteins have structural similarities to the antiphagocytic M protein, including the well-known C repeats. One of these molecules is the immunoglobulin A-binding protein Arp, which is expressed by a serotype 4 strain for which no antiphagocytic M protein has yet been described. We expressed Arp4 in an S. pyogenes strain from which the structural gene for the M protein has been deleted and found that Arp4 is not sufficient to inhibit phagocytosis.