This is a family of bacterial and viral bi-glutamic acid ADP-ribosyltransferases, where, in Swiss:Q93Q17, E403 is the catalytic residue and E401 contributes to the transfer of ADP-ribose to the target protein. In clostridial species it is actin that is being ADP-ribosylated; this result is lethal and dermonecrotic in infected mammals.

1: Pseudomonas aeruginosa exoenzyme S is a biglutamic acid ADP-ribosyltransferase. Radke J, Pederson KJ, Barbieri JT; Infect Immun. 1999;67:1508-1510. PMID:10024602

2: Crystal structure and site-directed mutagenesis of enzymatic components from Clostridium perfringens iota-toxin. Tsuge H, Nagahama M, Nishimura H, Hisatsune J, Sakaguchi Y, Itogawa Y, Katunuma N, Sakurai J; J Mol Biol. 2003;325:471-483. PMID:12498797