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1m0i
From Proteopedia
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Crystal Structure of Bacteriophage T7 Endonuclease I with a Wild-Type Active Site
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
1M0I is a Single protein structure of sequence from Bacteriophage t7 with SO4 as ligand. Active as Deoxyribonuclease IV (phage-T(4)-induced), with EC number 3.1.21.2 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 Tue Nov 20 21:02:08 2007
