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Figure 3.
Figure 3. Superpositions of I-CeuI and I-CreI
(A and B)
Superposition of I-CeuI is shown in green, and superposition of
I-CreI is shown in blue. Superpositions shown from the (A) side
and (B) bottom of the enzyme. The LAGLIDADG helices are shown in
the same orientations to the right. The rmsd for backbone atoms
of individual subunits is  vert,
similar 2 Å. The relative orientation of the two
DNA-contacting β platforms, calculated from the bottom of the
conserved LAGLIDADG helices, differs by vert,
similar 5° (indicated by a black arrow). This difference is
caused by a shift in the packing of the LAGLIDADG helix against
the corresponding enzyme core in each subunit (indicated by a
red arrow for one subunit), rather than by a rigid body rotation
of the two subunits.
(C) Left: Magnification of the
superimposed dimer interfaces of I-CeuI and I-CreI, which
contain the conserved residues of their respective active sites.
Right: The same orientation with only the I-CeuI interface and
active sites shown. Catalytic residues of I-CreI are blue, and
those of I-CeuI are colored by element type. A single bound
calcium ion in the I-CeuI structure is shown; the corresponding
anomalous difference density is shown in the right panel. The
calcium is bound between the scissile phosphates and the
corresponding metal binding residues. The Q93 residue of I-CeuI
is modeled from the crystal structure of the Q93R mutant used to
solve its structure. Figure 3. Superpositions of I-CeuI and
I-CreI(A and B) Superposition of I-CeuI is shown in green, and
superposition of I-CreI is shown in blue. Superpositions shown
from the (A) side and (B) bottom of the enzyme. The LAGLIDADG
helices are shown in the same orientations to the right. The
rmsd for backbone atoms of individual subunits is [3]not, vert,
similar 2 Å. The relative orientation of the two
DNA-contacting β platforms, calculated from the bottom of the
conserved LAGLIDADG helices, differs by [4]not, vert, similar
5° (indicated by a black arrow). This difference is caused
by a shift in the packing of the LAGLIDADG helix against the
corresponding enzyme core in each subunit (indicated by a red
arrow for one subunit), rather than by a rigid body rotation of
the two subunits.(C) Left: Magnification of the superimposed
dimer interfaces of I-CeuI and I-CreI, which contain the
conserved residues of their respective active sites. Right: The
same orientation with only the I-CeuI interface and active sites
shown. Catalytic residues of I-CreI are blue, and those of
I-CeuI are colored by element type. A single bound calcium ion
in the I-CeuI structure is shown; the corresponding anomalous
difference density is shown in the right panel. The calcium is
bound between the scissile phosphates and the corresponding
metal binding residues. The Q93 residue of I-CeuI is modeled
from the crystal structure of the Q93R mutant used to solve its
structure.
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