Crystal structure of Citrobacter freundii restriction endonuclease Cfr10I at 2.15 A resolution.

The X-ray crystal structure of Citrobacter freundii restriction endonuclease Cfr10I has been determined at a resolution of 2.15 A by multiple isomorphous replacement methods and refined to an R-factor of 19.64%. The structure of Cfr10I represents the first structure of a restriction endonuclease recognizing a degenerated nucleotide sequence. Structural comparison of Cfr10I with previously solved structures of other restriction enzymes suggests that recognition of specific sequence occurs through contacts in the major and the minor grooves of DNA. The arrangement of the putative active site residues shows some striking differences from previously described restriction endonucleases and supports a two-metal-ion mechanism of catalysis.