This domain is structurally very similar [1] to the creatinase N-terminal domain (Pfam:PF01321). However, little or no sequence similarity exists between the two families.

1: Structure and mechanism of a proline-specific aminopeptidase from Escherichia coli. Wilce MC, Bond CS, Dixon NE, Freeman HC, Guss JM, Lilley PE, Wilce JA; Proc Natl Acad Sci U S A 1998;95:3472-3477. PMID:9520390