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1m0d
From Proteopedia
Crystal Structure of Bacteriophage T7 Endonuclease I with a Wild-Type Active Site and Bound Manganese Ions
Overview
T7 endonuclease I is a nuclease that is selective for the structure of the four-way DNA junction. The active site is similar to those of a number of restriction enzymes. We have solved the crystal structure of endonuclease I with a wild-type active site. Diffusion of manganese ions into the crystal revealed two peaks of electron density per active site, defining two metal ion-binding sites. Site 1 is fully occupied, and the manganese ion is coordinated by the carboxylate groups of Asp55 and Glu65, and the main chain carbonyl of Thr66. Site 2 is partially occupied, and the metal ion has a single protein ligand, the remaining carboxylate oxygen atom of Asp55. Isothermal titration calorimetry showed the sequential exothermic binding of two manganese ions in solution, with dissociation constants of 0.58 +/- 0.019 and 14 +/- 1.5 mM. These results are consistent with a two metal ion mechanism for the cleavage reaction, in which the hydrolytic water molecule is contained in the first coordination sphere of the site 1-bound metal ion.
About this Structure
1M0D is a Single protein structure of sequence from Enterobacteria phage t7. Full crystallographic information is available from OCA.
Reference
Metal ions bound at the active site of the junction-resolving enzyme T7 endonuclease I., Hadden JM, Declais AC, Phillips SE, Lilley DM, EMBO J. 2002 Jul 1;21(13):3505-15. PMID:12093751 Page seeded by OCA on Sat May 3 00:28:47 2008
