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PDBsum entry 5f6t
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Calcium-binding protein
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PDB id
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5f6t
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References listed in PDB file
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Key reference
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Title
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Binding of gd(3+) to the neuronal signalling protein calexcitin identifies an exchangeable ca(2+)-Binding site.
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Authors
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L.Chataigner,
J.Guo,
P.T.Erskine,
A.R.Coker,
S.P.Wood,
Z.Gombos,
J.B.Cooper.
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Ref.
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Acta Crystallogr F Struct Biol Commun, 2016,
72,
276-281.
[DOI no: ]
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PubMed id
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Abstract
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Calexcitin was first identified in the marine snail Hermissenda crassicornis as
a neuronal-specific protein that becomes upregulated and phosphorylated in
associative learning. Calexcitin possesses four EF-hand motifs, but only the
first three (EF-1 to EF-3) are involved in binding metal ions. Past work has
indicated that under physiological conditions EF-1 and EF-2 bind Mg(2+) and
Ca(2+), while EF-3 is likely to bind only Ca(2+). The fourth EF-hand is
nonfunctional owing to a lack of key metal-binding residues. The aim of this
study was to use a crystallographic approach to determine which of the three
metal-binding sites of calexcitin is most readily replaced by exogenous metal
ions, potentially shedding light on which of the EF-hands play a `sensory' role
in neuronal calcium signalling. By co-crystallizing recombinant calexcitin with
equimolar Gd(3+) in the presence of trace Ca(2+), EF-1 was shown to become fully
occupied by Gd(3+) ions, while the other two sites remain fully occupied by
Ca(2+). The structure of the Gd(3+)-calexcitin complex has been refined to an R
factor of 21.5% and an Rfree of 30.4% at 2.2 Å resolution. These findings
suggest that EF-1 of calexcitin is the Ca(2+)-binding site with the lowest
selectivity for Ca(2+), and the implications of this finding for calcium sensing
in neuronal signalling pathways are discussed.
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