<prompt> Answer this question truthfullyWhat is the function of M protein in relation to the complement system, and what specific molecules does it interact with?  <response>: <reason> M protein is a virulence factor produced by Streptococcus pyogenes GAS bacteria that interacts with the complement system. Specifically, M protein binds to factor H, a regulatory protein in the complement pathway, and breaks down C3-convertase, an enzyme complex involved in the activation of the complement system. This allows GAS to evade the immune system and establish infection in the host. 