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.
Figure 4.
Figure 4. Topological diagrams of Cfr10I (a), EcoRI (b) and EcoRV (c) at the same orientation as in Figure 3. Common
structural elements are shadowed. Dimerisation regions are emphasised in blue and structural elements that contact
DNA are in red.
Figure 5.
Figure 5. Stereo view of the superimposition of the DNA-recognition region of Cfr10I (red) on BamHI (purple).
Residue R155 in BamHI is supposed to contact the outer base-pair of the recognition sequence.
The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(1996,
255,
176-186)
copyright 1996.
