View source for 1mz8

[[Image:1mz8.gif|left|200px]]

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{{STRUCTURE_1mz8|  PDB=1mz8  |  SCENE=  }} 

'''CRYSTAL STRUCTURES OF THE NUCLEASE DOMAIN OF COLE7/IM7 IN COMPLEX WITH A PHOSPHATE ION AND A ZINC ION'''


==Overview==
H-N-H is a motif found in the nuclease domain of a subfamily of bacteria toxins, including colicin E7, that are capable of cleaving DNA nonspecifically. This H-N-H motif has also been identified in a subfamily of homing endonucleases, which cleave DNA site specifically. To better understand the role of metal ions in the H-N-H motif during DNA hydrolysis, we crystallized the nuclease domain of colicin E7 (nuclease-ColE7) in complex with its inhibitor Im7 in two different crystal forms, and we resolved the structures of EDTA-treated, Zn(2+)-bound and Mn(2+)-bound complexes in the presence of phosphate ions at resolutions of 2.6 A to 2.0 A. This study offers the first determination of the structure of a metal-free and substrate-free enzyme in the H-N-H family. The H-N-H motif contains two antiparallel beta-strands linked to a C-terminal alpha-helix, with a divalent metal ion located in the center. Here we show that the metal-binding sites in the center of the H-N-H motif, for the EDTA-treated and Mg(2+)-soaked complex crystals, were occupied by water molecules, indicating that an alkaline earth metal ion does not reside in the same position as a transition metal ion in the H-N-H motif. However, a Zn(2+) or Mn(2+) ions were observed in the center of the H-N-H motif in cases of Zn(2+) or Mn(2+)-soaked crystals, as confirmed in anomalous difference maps. A phosphate ion was found to bridge between the divalent transition metal ion and His545. Based on these structures and structural comparisons with other nucleases, we suggest a functional role for the divalent transition metal ion in the H-N-H motif in stabilizing the phosphoanion in the transition state during hydrolysis.

==About this Structure==
1MZ8 is a [[Protein complex]] structure of sequences from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1MZ8 OCA]. 

==Reference==
Metal ions and phosphate binding in the H-N-H motif: crystal structures of the nuclease domain of ColE7/Im7 in complex with a phosphate ion and different divalent metal ions., Sui MJ, Tsai LC, Hsia KC, Doudeva LG, Ku WY, Han GW, Yuan HS, Protein Sci. 2002 Dec;11(12):2947-57. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/12441392 12441392]
[[Category: Escherichia coli]]
[[Category: Protein complex]]
[[Category: Doudeva, L G.]]
[[Category: Han, G W.]]
[[Category: Hsia, K C.]]
[[Category: Ku, W Y.]]
[[Category: Sui, M J.]]
[[Category: Tsai, L C.]]
[[Category: Yuan, H S.]]
[[Category: H-n-h motif]]
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