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

DOI: 10.1107/S2053230X16003526 DOI Help

Authors: Lucas Chataigner (University College London (UCL)) , Jingxu Guo (University College London) , Peter Erskine (Royal Free and University College Medical School) , Alun Coker (University College Medical School, UCL Divisision of Medicine) , Steve P. Wood (University College London) , Zoltan Gombos (University of Alberta) , Jonathan Cooper (University College London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Crystallographica Section F Structural Biology Communications , VOL 72 (4) , PAGES 276 - 281

State: Published (Approved)
Published: April 2016
Diamond Proposal Number(s): 12342

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 Mg2+ and Ca2+, while EF-3 is likely to bind only Ca2+. 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 Gd3+ in the presence of trace Ca2+, EF-1 was shown to become fully occupied by Gd3+ ions, while the other two sites remain fully occupied by Ca2+. The structure of the Gd3+–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 Ca2+-binding site with the lowest selectivity for Ca2+, and the implications of this finding for calcium sensing in neuronal signalling pathways are discussed.

Journal Keywords: Neuronal calcium signalling; EF-hand; protein structure; heavy-atom complex; co-crystallization.

Subject Areas: Medicine, Biology and Bio-materials

Instruments: I04-Macromolecular Crystallography

Added On: 31/03/2016 11:27

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