PDBsum entry 5f6t

Calcium-binding protein

PDB id: 5f6t

Contents

Protein chain

185 a.a.

Metals

_CA ×2

_GD

Waters ×30

PDB id:

5f6t

Name:

Calcium-binding protein

Title:

Structure of calexcitin-gd3+ complex.

Structure:

Calexcitin. Chain: a. Engineered: yes

Source:

Doryteuthis pealeii. Longfin inshore squid. Organism_taxid: 1051067. Gene: cex. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008.

Resolution:

2.20Å R-factor: 0.219 R-free: 0.304

Authors:

L.Chataigner,J.Guo,P.T.Erskine,A.R.Coker,S.P.Wood,J.B.Cooper

Key ref:

L.Chataigner et al. (2016). Binding of Gd(3+) to the neuronal signalling protein calexcitin identifies an exchangeable Ca(2+)-binding site. Acta Crystallogr F Struct Biol Commun, 72, 276-281. PubMed id: 27050260 DOI: 10.1107/S2053230X16003526

Date:

06-Dec-15 Release date: 16-Dec-15

Protein chain

O76764  (O76764_DORPE) -  Calexcitin from Doryteuthis pealeii

Seq: 191 a.a.

Struc: 185 a.a.

DOI no: 10.1107/S2053230X16003526

Acta Crystallogr F Struct Biol Commun 72:276-281 (2016)

PubMed id: 27050260

Binding of Gd(3+) to the neuronal signalling protein calexcitin identifies an exchangeable Ca(2+)-binding site.

L.Chataigner, J.Guo, P.T.Erskine, A.R.Coker, S.P.Wood, Z.Gombos, J.B.Cooper.

ABSTRACT

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.