Figure 4.
FIG. 4. Simulated annealing omit maps around the active
site for the complexes of H103A E9 DNase·dsDNA bound to
Zn2+ (A) and Mg2+ (B). The metal ion, the scissile phosphate,
and histidines 102, 127, and 131 were omitted for the
calculation, and the resulting maps were plotted at a contour
level of 2.0 . The coordination of
both metal ions is indicated with dotted lines. The figure
highlights how the H-N-H motif is an adaptable metal binding
center. It is able to accommodate both the tetrahedral
coordination chemistry of a Zn2+ ion (A) and then, through
subtle reorientations of the H-N-H histidine residues and the
inclusion of DNA phosphodiester oxygen atoms and a water
molecule, the octahedral geometry required for Mg2+ ion binding
(B). Only five of the possible six coordination sites are
discernible for the Mg2+ ion at the current level of resolution.
The above figure is reprinted
by permission from the ASBMB:
J Biol Chem
(2004,
279,
34763-34769)
copyright 2004.
. The coordination of
both metal ions is indicated with dotted lines. The figure
highlights how the H-N-H motif is an adaptable metal binding
center. It is able to accommodate both the tetrahedral
coordination chemistry of a Zn2+ ion (A) and then, through
subtle reorientations of the H-N-H histidine residues and the
inclusion of DNA phosphodiester oxygen atoms and a water
molecule, the octahedral geometry required for Mg2+ ion binding
(B). Only five of the possible six coordination sites are
discernible for the Mg2+ ion at the current level of resolution.