Alignment of amino acid sequence of catalytic domains of Porphyromonas gingivalis PAD (PPAD) (residues 86 to 363), AIH from Dyadobacter fermentans DSM 18053 (locus Dfer_2630, residues 60 to 352), and human PAD4 (residues 306 to 556). Residues identical in PPAD and AIH and/or PAD4 are highlighted. Guanidino-binding (#) and catalytic residues (*) that are conserved in all families of guanidino-group modifying enzyme superfamily are indicated. The amino-terminal sequence of each enzyme is unique. In PAD4, the amino-terminal portion is folded into two consecutive immunoglobulin-like β-sandwich domains preceding the catalytic domain harboring the α/β-propeller fold . A long 200-residue carboxy-terminal extension of PPAD is predicted to adopt an immunoglobulin-like β-sandwich structure . AIH, agmatine iminohydrolase; PAD, peptidylarginine deiminase.