1m0d
From Proteopedia
Crystal Structure of Bacteriophage T7 Endonuclease I with a Wild-Type Active Site and Bound Manganese Ions
Structural highlights
Function[ENDO_BPT7] Junction-resolving enzyme that selectively binds and cleaves four-way (Holliday) DNA junctions present after viral genomic replication. These intermediates are created during DNA repair, processing of stalled replication forks and homologous genetic recombination. Introduces two nicks on the two non-crossing strands, at 5' sides of the junction. Participates also together with gp6 in the degradation of host chromosome to provide nucleotides for phage DNA synthesis.[1] [2] [3] [4] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedT7 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. 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[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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