This family is found to carry modified motifs characteristic of PD-(D/E)XK endonuclease superfamily. These are the conserved Glu of motif I, the Asp surreounded by hydrophobics of motif II, EIKS of motif III, and the lysine of mmotif IV has migrated to an alpha-helix following the third core beta-strand. The conserved patch of positively charged lysine and arginine residues in the motif IV apha-helix might be involved in substrate-binding or be contributing to active site formation [2]. Members with an additional N-terminal coi9led-coil domain, are annotated as tropomyosin, coiled-coil or microtubule binding proteins [1,2].

1: Complete genome sequence of an aerobic hyper-thermophilic crenarchaeon, Aeropyrum pernix K1. Kawarabayasi Y, Hino Y, Horikawa H, Yamazaki S, Haikawa Y, Jin-no K, Takahashi M, Sekine M, Baba S, Ankai A, Kosugi H, Hosoyama A, Fukui S, Nagai Y, Nishijima K, Nakazawa H, Takamiya M, Masuda S, Funahashi T, Tanaka T, Kudoh Y, Yamazaki J, Kushida N, Oguc DNA Res 1999;6:83-101. PMID:10382966

2: 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