Members of this family, which are predominantly found in anthrax toxin lethal factor, adopt a structure consisting of a core of antiparallel beta sheets and alpha helices. They form a long deep groove within the protein that anchors the 16-residue N-terminal tail of MAPKK-2 before cleavage. It has been noted that this domain resembles the ADP-ribosylating toxin from Bacillus cereus, but the active site has been modified to augment substrate recognition [1].

1: Crystal structure of the anthrax lethal factor. Pannifer AD, Wong TY, Schwarzenbacher R, Renatus M, Petosa C, Bienkowska J, Lacy DB, Collier RJ, Park S, Leppla SH, Hanna P, Liddington RC; Nature. 2001;414:229-233. PMID:11700563