This domain is found mostly in bacteria. It is found at the C-terminal of Shedu protein SduA, the only component of antiviral defense system Shedu. Expression of Shedu in B.subtilis (strain BEST7003) confers resistance to phages phi105, phi29, rho14 and to a lesser extent to SPP1 [2]. This domain may have endonuclease activity [1].

1: Sequence, structure and functional diversity of PD-(D/E)XK phosphodiesterase superfamily. Steczkiewicz K, Muszewska A, Knizewski L, Rychlewski L, Ginalski K; Nucleic Acids Res. 2012;40:7016-7045. PMID:22638584

2: Systematic discovery of antiphage defense systems in the microbial pangenome. Doron S, Melamed S, Ofir G, Leavitt A, Lopatina A, Keren M, Amitai G, Sorek R; Science. 2018; [Epub ahead of print] PMID:29371424