Cyclic phosphodiesterase (CPDase) is involved in the tRNA splicing pathway. This protein exhibits a bilobal arrangement of two alpha-beta modules. Two antiparallel helices are found on the outer side of each lobe and frame an antiparallel beta-sheet that is wrapped around an accessible cleft. Moreover, the beta-strands of each lobe interact with the other lobe. The central water-filled cavity houses the enzyme's active site.