Cfr10I (Swiss:P56200) and Bse634I (Swiss:Q8RT53) are two Type II restriction endonucleases. They exhibit a conserved tetrameric architecture that is of functional importance, wherein two dimers are arranged 'back-to-back' with their putative DNA-binding clefts facing opposite directions. These clefts are formed between two monomers that interact, mainly via hydrophobic interactions supported by a few hydrogen bonds, to form a U-shaped dimer. Each monomer is folded to form a compact alpha-beta structure, whose core is made up of a five-stranded mixed beta-sheet.The monomer may be split into separate N-terminal and C-terminal subdomains at a hinge located in helix alpha3 [1].

1: Crystal structure of the Bse634I restriction endonuclease: comparison of two enzymes recognizing the same DNA sequence. Grazulis S, Deibert M, Rimseliene R, Skirgaila R, Sasnauskas G, Lagunavicius A, Repin V, Urbanke C, Huber R, Siksnys V; Nucleic Acids Res 2002;30:876-885. PMID:11842098

2: 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