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 ions1 Graduate Institute of Life
Science, National Defense Medical Center, Taipei, Taiwan 11472, ROC
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, Zn2+-bound and Mn2+-bound
complexes in the presence of phosphate ions at resolutions of 2.6 Å
to 2.0 Å. 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 ß-strands linked to a
C-terminal Keywords: Metal binding in proteins; divalent metal ions; magnesium ion; zinc ion; endonuclease; DNase; DNA hydrolysis mechanism Protein Science (2002), 11:2947-2957. |
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