Dataset Information

Structure-Functional Basis of Ion Transport in Sodium-Calcium Exchanger (NCX) Proteins.

ABSTRACT: The membrane-bound sodium-calcium exchanger (NCX) proteins shape Ca2+ homeostasis in many cell types, thus participating in a wide range of physiological and pathological processes. Determination of the crystal structure of an archaeal NCX (NCX_Mj) paved the way for a thorough and systematic investigation of ion transport mechanisms in NCX proteins. Here, we review the data gathered from the X-ray crystallography, molecular dynamics simulations, hydrogen-deuterium exchange mass-spectrometry (HDX-MS), and ion-flux analyses of mutants. Strikingly, the apo NCX_Mj protein exhibits characteristic patterns in the local backbone dynamics at particular helix segments, thereby possessing characteristic HDX profiles, suggesting structure-dynamic preorganization (geometric arrangements of catalytic residues before the transition state) of conserved ?? and ?? repeats at ion-coordinating residues involved in transport activities. Moreover, dynamic preorganization of local structural entities in the apo protein predefines the status of ion-occlusion and transition states, even though Na? or Ca2+ binding modifies the preceding backbone dynamics nearby functionally important residues. Future challenges include resolving the structural-dynamic determinants governing the ion selectivity, functional asymmetry and ion-induced alternating access. Taking into account the structural similarities of NCX_Mj with the other proteins belonging to the Ca2+/cation exchanger superfamily, the recent findings can significantly improve our understanding of ion transport mechanisms in NCX and similar proteins.

SUBMITTER: Giladi M

PROVIDER: S-EPMC5133943 | biostudies-literature | 2016 Nov

REPOSITORIES: biostudies-literature

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Structure-Functional Basis of Ion Transport in Sodium-Calcium Exchanger (NCX) Proteins.

Giladi Moshe M Shor Reut R Lisnyansky Michal M Khananshvili Daniel D

International journal of molecular sciences 20161122 11

The membrane-bound sodium-calcium exchanger (NCX) proteins shape Ca<sup>2+</sup> homeostasis in many cell types, thus participating in a wide range of physiological and pathological processes. Determination of the crystal structure of an archaeal NCX (NCX_Mj) paved the way for a thorough and systematic investigation of ion transport mechanisms in NCX proteins. Here, we review the data gathered from the X-ray crystallography, molecular dynamics simulations, hydrogen-deuterium exchange mass-spectr ...[more]

PMID: 27879668

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Project description:Na(+)/Ca(2+) exchanger (NCX) proteins extrude Ca(2+) from the cell to maintain cellular homeostasis. Since NCX proteins contribute to numerous physiological and pathophysiological events, their pharmacological targeting has been desired for a long time. This intervention remains challenging owing to our poor understanding of the underlying structure-dynamic mechanisms. Recent structural studies have shed light on the structure-function relationships underlying the ion-transport and allosteric regulation of NCX. The crystal structure of an archaeal NCX (NCX_Mj) along with molecular dynamics simulations and ion flux analyses, have assigned the ion binding sites for 3Na(+) and 1Ca(2+), which are being transported in separate steps. In contrast with NCX_Mj, eukaryotic NCXs contain the regulatory Ca(2+)-binding domains, CBD1 and CBD2, which affect the membrane embedded ion-transport domains over a distance of ~80 Å. The Ca(2+)-dependent regulation is ortholog, isoform, and splice-variant dependent to meet physiological requirements, exhibiting either a positive, negative, or no response to regulatory Ca(2+). The crystal structures of the two-domain (CBD12) tandem have revealed a common mechanism involving a Ca(2+)-driven tethering of CBDs in diverse NCX variants. However, dissociation kinetics of occluded Ca(2+) (entrapped at the two-domain interface) depends on the alternative-splicing segment (at CBD2), thereby representing splicing-dependent dynamic coupling of CBDs. The HDX-MS, SAXS, NMR, FRET, equilibrium (45)Ca(2+) binding and stopped-flow techniques provided insights into the dynamic mechanisms of CBDs. Ca(2+) binding to CBD1 results in a population shift, where more constraint conformational states become highly populated without global conformational changes in the alignment of CBDs. This mechanism is common among NCXs. Recent HDX-MS studies have demonstrated that the apo CBD1 and CBD2 are stabilized by interacting with each other, while Ca(2+) binding to CBD1 rigidifies local backbone segments of CBD2, but not of CBD1. The extent and strength of Ca(2+)-dependent rigidification at CBD2 is splice-variant dependent, showing clear correlations with phenotypes of matching NCX variants. Therefore, diverse NCX variants share a common mechanism for the initial decoding of the regulatory signal upon Ca(2+) binding at the interface of CBDs, whereas the allosteric message is shaped by CBD2, the dynamic features of which are dictated by the splicing segment.

Dataset Information

Structure-Functional Basis of Ion Transport in Sodium-Calcium Exchanger (NCX) Proteins.

Publications

Structure-Functional Basis of Ion Transport in Sodium-Calcium Exchanger (NCX) Proteins.

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