This domain has been identified as a member of the PD-(D/E)XK nuclease superfamily through transitive meta profile searches [1]. The domain has two additional beta-strands inserted to the core fold after the first core alpha-helix. It has been speculated that it could function as s methylation-dependent restriction [1]. The domain has two additional beta-strands inserted into the core fold after the first core alpha-helix. The PD-(D/E)XK signature is clearly conserved corresponding to an invariant PD (motif II) and DAK (motif III) motifs. There is also a conserved glutamic acid in motif I that is most likely to be involved in metal ion binding. The second core alpha-helix contains an invariant MHXYRD motif. It has been speculated that it could function as s methylation-dependent restriction enzyme [1].

1: Realm of PD-(D/E)XK nuclease superfamily revisited: detection of novel families with modified transitive meta profile searches. Knizewski L, Kinch LN, Grishin NV, Rychlewski L, Ginalski K; BMC Struct Biol. 2007;7:40. PMID:17584917