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PDBsum entry 1s3p
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Calcium-binding protein
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PDB id
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1s3p
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Contents |
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* Residue conservation analysis
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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 of a high-Affinity variant of rat alpha-Parvalbumin.
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Authors
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Y.H.Lee,
J.J.Tanner,
J.D.Larson,
M.T.Henzl.
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Ref.
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Biochemistry, 2004,
43,
10008-10017.
[DOI no: ]
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PubMed id
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Abstract
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In model peptide systems, Ca2+ affinity is maximized in EF-hand motifs
containing four carboxylates positioned on the +x and -x and +z and -z axes;
introduction of a fifth carboxylate ligand reduces the affinity. However, in rat
beta-parvalbumin, replacement of Ser-55 with aspartate heightens divalent ion
affinity [Henzl, M. T., et al. (1996) Biochemistry 35, 5856-5869]. The
corresponding alpha-parvalbumin variant (S55D/E59D) likewise exhibits elevated
affinity [Henzl, M. T., et al. (2003) Anal. Biochem. 319, 216-233]. To determine
whether these mutations produce a variation on the archetypal EF-hand
coordination scheme, we have obtained high-resolution X-ray crystallographic
data for alpha S55D/E59D. As anticipated, the aspartyl carboxylate replaces the
serine hydroxyl at the +z coordination position. Interestingly, the Asp-59
carboxylate abandons the role it plays as an outer sphere ligand in wild-type
rat beta, rotating away from the Ca2+ and, instead, forming a hydrogen bond with
the amide of Glu-62. Superficially, the coordination sphere in the CD site of
alpha S55D/E59D resembles that in the EF site. However, the orientation of the
Asp-59 side chain is predicted to stabilize the D-helix, which may contribute to
the heightened divalent ion affinity. DSC data indicate that the alpha S55D/E59D
variant retains the capacity to bind 1 equiv of Na+. Consistent with this
finding, when binding measurements are conducted in K(+)-containing buffer,
divalent ion affinity is markedly higher. In 0.15 M KCl and 0.025 M Hepes-KOH
(pH 7.4) at 5 degrees C, the macroscopic Ca2+ binding constants are 1.8 x 10(10)
and 2.0 x 10(9) M(-1). The corresponding Mg2+ binding constants are 2.7 x 10(6)
and 1.2 x 10(5) M(-1).
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