1m0d: Difference between revisions

[[Image:1m0d.jpg|left|200px]]<br /><applet load="1m0d" size="350" color="white" frame="true" align="right" spinBox="true"  

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.

1M0D is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Bacteriophage_t7 Bacteriophage t7] with <scene name='pdbligand=MN:'>MN</scene> and <scene name='pdbligand=SO4:'>SO4</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Deoxyribonuclease_IV_(phage-T(4)-induced) Deoxyribonuclease IV (phage-T(4)-induced)], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.1.21.2 3.1.21.2] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1M0D OCA].  

[[Category: Declais, A C.]]

[[Category: Hadden, J M.]]

[[Category: Lilley, D M.]]

[[Category: Phillips, S E.]]

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