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PDBsum entry 2ev7
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Metal binding protein
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PDB id
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2ev7
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References listed in PDB file
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Key reference
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Title
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Structural basis for the observed differential magnetic anisotropic tensorial values in calcium binding proteins.
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Authors
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S.M.Mustafi,
S.Mukherjee,
K.V.Chary,
G.Cavallaro.
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Ref.
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Proteins, 2006,
65,
656-669.
[DOI no: ]
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PubMed id
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Note In the PDB file this reference is
annotated as "TO BE PUBLISHED".
The citation details given above were identified by an automated
search of PubMed on title and author
names, giving a
percentage match of
95%.
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Abstract
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Lanthanide ions (Ln(3+)), which have ionic radii similar to those of Ca(2+), can
displace the latter in a calcium binding protein, without affecting its tertiary
structure. The paramagnetic Ln(3+) possesses large anisotropic magnetic
susceptibilities and produce pseudocontact shifts (PCSs), which have r(-3)
dependence. The PCS can be seen for spins as far as 45 A from the paramagnetic
ion. They aid in structure refinement of proteins by providing long-range
distance constraints. Besides, they can be used to determine the interdomain
orientation in multidomain proteins. This is particularly important in the
context of a calcium binding protein from Entamoeba histolytica (EhCaBP), which
consists of two globular domains connected by a flexible linker region
containing 8 residues. As a first step to obtain the interdomain orientation in
EhCaBP, a suite of 2D and 3D heteronuclear experiments were recorded on EhCaBP
by displacing calcium with Ce(3+), Ho(3+), Er(3+), Tm(3+), Dy(3+), and Yb(3+)
ions in separate experiments, and the PCS of (1)H(N) and (15)N spins were
measured. Such data have been used in the refinement of the individual domain
structures of the protein in parallel with the calculation of the respective
magnetic anisotropy tensorial values, which differ substantially (2.1-2.8 times)
from what is found in other Ca(2+) binding loops. This study provides a
structural basis for such variations in the magnetic anisotropy tensorial values.
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Figure 2.
Figure 2. The dipolar nature of pseudo-contact interaction,
under point-point dipole approximation. The Ln^3+ ion is taken
as the origin of the co-ordinate system; r is the distance of a
particular nucleus in the protein from its paramagnetic center.
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Figure 7.
Figure 7. Various ^15N and ^1H^N PCS shifts seen in the
C-terminal domain of (Dy^3+/Tm^3+)(Ca^2+)[3]-EhCaBP, in
(Dy^3+)(Ca^2+)-Parvalbumin and in the N-terminal domain of (Tm
^3+)(Ca^2+)[3]Calmodulin (N60D), depicted as spheres using
MOLMOL. The red spheres represent the negative shifts, while
green ones are positive shifts. The radii of the spheres are
proportional to the magnitude of the observed shifts. The shifts
observed in (Dy^3+)(Ca^2+)-Parvalbumin and in N-terminal domain
of (Tm^3+)(Ca^2+)[3]-Calmodulin (N60D) are higher than
corresponding shifts in C-terminal domain of
(Dy^3+/Tm^3+)(Ca^2+)[3]-EhCaBP indicating higher strength of
ligand field in parvalbumin and calmodulin when compared with
C-terminal domain of EhCaBP. The blue sphere indicates the Ln^3+.
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The above figures are
reprinted
by permission from John Wiley & Sons, Inc.:
Proteins
(2006,
65,
656-669)
copyright 2006.
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