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PDBsum entry 3li6
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Metal binding protein
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PDB id
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3li6
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References listed in PDB file
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Key reference
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Title
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Crystal structure and trimer-Monomer transition of n-Terminal domain of ehcabp1 from entamoeba histolytica.
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Authors
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S.Kumar,
E.Ahmad,
M.S.Mansuri,
S.Kumar,
R.Jain,
R.H.Khan,
S.Gourinath.
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Ref.
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Biophys J, 2010,
98,
2933-2942.
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PubMed id
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Abstract
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EhCaBP1 is a well-characterized calcium binding protein from Entamoeba
histolytica with four canonical EF-hand motifs. The crystal structure of EhCaBP1
reveals the trimeric organization of N-terminal domain. The solution structure
obtained at pH 6.0 indicated its monomeric nature, similar to that of
calmodulin. Recent domain-wise studies showed clearly that the N-terminal domain
of EhCaBP1 is capable of performing most of the functions of the full-length
protein. Additionally, the mode of target binding in the trimer is similar to
that found in calmodulin. To study the dynamic nature of this protein and
further validate the trimerization of N-terminal domain at physiological
conditions, the crystal structure of N-terminal domain was determined at 2.5 A
resolution. The final structure consists of EF-1 and EF-2 motifs separated by a
long straight helix as seen in the full-length protein. The spectroscopic and
stability studies, like far and near-ultraviolet circular dichroism spectra,
intrinsic and extrinsic fluorescence spectra, acrylamide quenching, thermal
denaturation, and dynamic light scattering, provided clear evidence for a
conversion from trimeric state to monomeric state. As the pH was lowered from
the physiological pH, a dynamic trimer-monomer transition was observed. The
trimeric state and monomeric state observed in spectroscopic studies may
represent the x-ray and NMR structures of the EhCaBP1. At pH 6.0, the endogenous
kinase activation function was almost lost, indicating that the monomeric state
of the protein, where EF-hand motifs are far apart, is not a functional state.
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