PDDEXK_6 is a family of plant proteins that are distant homologues of the PD-(D/E)XK nuclease superfamily. The core structure is retained, as alpha-beta-beta-beta-alpha-beta. It retains the characteristic PDDEXK motifs II and III in modified forms - xDxxx motif located in the second core beta-strand, where x is any hydrophobic residue, and a D/E)X(D/N/S/C/G) pattern. The missing positively charged residue in motif III is possibly replaced by a conserved arginine in motif IV located in the proceeding alpha-helix [1]. The family is not in general fused with any other domains, so its function cannot be predicted [2].

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

2: Conserved Peptide Upstream Open Reading Frames are Associated with Regulatory Genes in Angiosperms. Jorgensen RA, Dorantes-Acosta AE; Front Plant Sci. 2012;3:191. PMID:22936940