Ionic regulation of the cardiac sodium-calcium exchanger

Reeves, John P.; Condrescu, Madalina

doi:10.4161/chan.2.5.6897

Cited by 32 publications

(26 citation statements)

References 63 publications

(76 reference statements)

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“…The NCX is the primary Ca 2ϩ extrusion mechanism in the heart and the brain (1)(2)(3). In addition to being substrates, Na ϩ and Ca 2ϩ also have regulatory functions: cytosolic Ca 2ϩ acts as an allosteric activator, while intracellular Na ϩ inhibits the exchanger.…”

mentioning

confidence: 99%

Ca2+ Binding Alters the Interdomain Flexibility between the Two Cytoplasmic Calcium-binding Domains in the Na+/Ca2+ Exchanger

Salinas

Bruschweiler‐Li

Johnson

et al. 2011

Journal of Biological Chemistry

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The Na ؉ /Ca 2؉ exchanger (NCX) is a membrane protein, which catalyzes the counter transport of Na ؉ and Ca 2؉ ions across the plasma membrane, playing a key role in the maintenance of the intracellular Ca 2؉ homeostasis in various cell types. NCX consists of a transmembrane part and a large intracellular loop. The activation of the NCX transport function requires the binding of Ca 2؉ to two tandem C2 domains, CBD1 and CBD2, which are an integral part of the exchanger's intracellular loop. Although high-resolution structures of individual CBD1 and CBD2 are available, their interdomain structure and dynamics and the atomic level mechanism of allosteric Ca 2؉ -regulation remains unknown. Here, we use solution NMR spectroscopy to study the interdomain dynamics of CBD12, a 32 kDa construct that contains both the CBD1 and CBD2 domains connected by a short linker. Analysis of NMR residual dipolar couplings shows that CBD12 assumes on average an elongated shape both in the absence and in the presence of Ca 2؉ . NMR 15 N relaxation data of the Apo state indicate that the two domains sample a wide range of relative arrangements on the nanosecond time scale. These arrangements comprise significantly non-linear interdomain orientations. Binding of Ca 2؉ to CBD1 significantly restricts the interdomain flexibility, stabilizing a more rigid elongated conformation. These findings suggest a molecular mechanism for the role of CBD12 in the function of NCX.The Na ϩ /Ca 2ϩ exchanger (NCX) 4 is a membrane protein that maintains intracellular Ca 2ϩ homeostasis. The NCX is the primary Ca 2ϩ extrusion mechanism in the heart and the brain (1-3). In addition to being substrates, Na ϩ and Ca 2ϩ also have regulatory functions: cytosolic Ca 2ϩ acts as an allosteric activator, while intracellular Na ϩ inhibits the exchanger. The latter process, called Na ϩ -dependent inactivation, can be reversed by the increase of intracellular Ca 2ϩ (2, 3). The mature canine NCX1 consists of two transmembrane regions, formed by 5 and 4 transmembrane segments (TM), separated by a large intracellular loop between TM5 and TM6 (2, 3). The intracellular loop contains two tandem calciumbinding domains (CBDs), CBD1 (residues 371-501) and CBD2 (residues 504 -657 in the AD splice variant studied here) (4). The CBD domains share an immunoglobulin (Ig) fold, formed by two antiparallel ␤-sheets, which pack against each other forming a ␤-sandwich, and a large unstructured loop connecting strands F and G at the opposite side of the ␤-sandwich (4 -8). CBD1 and CBD2 bind four and two Ca 2ϩ ions, respectively (5, 6). The Ca 2ϩ -binding sites lie at the tip of the ␤-sandwich. This topology is very similar to C2 domains, a class of Ca 2ϩ -binding motifs that are ubiquitous in nature, and frequently involved in signal transduction and membrane traffic (9).While the transmembrane regions of the exchanger conduct ion transport (3, 10), extensive electrophysiological data obtained with the wild type and mutant exchangers have implicated CBD1 and CBD2 in Ca 2ϩ regulation (6, 11,...

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confidence: 99%

Ca2+ Binding Alters the Interdomain Flexibility between the Two Cytoplasmic Calcium-binding Domains in the Na+/Ca2+ Exchanger

Salinas

Bruschweiler‐Li

Johnson

et al. 2011

Journal of Biological Chemistry

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“…In cellular systems, 0.3-10 M cytosolic Ca 2ϩ can activate NCX1 within a few milliseconds, whereas lower Ca 2ϩ levels (Ͻ0.3 M) activate the exchanger more slowly (for review see Ref. 29). Moreover, the secondary regulation of NCX, referred to as Ca 2ϩ -dependent inactivation (I 2 ) is a slow process (t 0.5 ϭ ϳ3-7 s) (30 -32) that considerably varies among NCX splice variants (8,9).…”

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confidence: 99%

Essential Role of the CBD1-CBD2 Linker in Slow Dissociation of Ca2+ from the Regulatory Two-domain Tandem of NCX1

Giladi

Boyman

Mikhasenko

et al. 2010

Journal of Biological Chemistry

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In NCX proteins CBD1 and CBD2 domains are connected through a short linker (3 or 4 amino acids) forming a regulatory tandem (CBD12). Only three of the six CBD12 Ca , whereas the kinetic and equilibrium properties of three Ca 2؉ sites of CBD12-7Ala and CBD1 ؉ CBD2 are similar. Therefore, the linker-dependent interactions in CBD12 decelerate the Ca 2؉ on/off kinetics at a specific CBD1 site by 50 -80-fold, thereby representing Ca 2؉ "occlusion" at CBD12. Notably, the kinetic and equilibrium properties of the remaining two sites of CBD12 are "linker-independent," so their intrinsic properties are preserved in CBD12. In conclusion, the dynamic properties of three sites are specifically modified, conserved, diversified, and integrated by the linker in CBD12, thereby generating a wide range dynamic sensor.The Na ϩ /Ca 2ϩ exchanger proteins (NCX1-3) and their splice variants are expressed in a tissue-specific manner (1-3) and mediate Ca 2ϩ entry/extrusion depending on various factors (4, 5). NCX is "autoregulated" by cytosolic Ca 2ϩ at sites that do not directly participate in the ion translocation (6, 7). For example, the cardiac/neuronal NCX1 variants respond to 0.3-10 M cytosolic Ca 2ϩ , whereas the kidney variant does not (8, 9). Allosteric regulation of NCX involves the interaction of cytosolic Ca 2ϩ with the regulatory loop-f of NCX (10 -14). Although the high affinity regulatory site of NCX1 was discovered 16 years ago (15), only recent studies identified two Ca 2ϩ regulatory domains, CBD1 and CBD2, which form a tandem (CBD12) through a short linker (amino acids 501-504) (16). High resolution x-ray and NMR revealed C 2 -type protein folding in both CBDs (16 -20) that display four Ca 2ϩ sites (Ca1-Ca4) on CBD1 (17,18,20) and two Ca 2ϩ sites (CaI and CaII) on CBD2 (16, 19). The NCX splice variants arise from a combination of 6 small exons (A, B, C, D, E, F), while the splice variant region is exclusively restricted to the CBD2 domain (2-4, 16, 19, 24). Excitable tissues, such as those of the brain (AD splice variant) and heart (ACDEF splice variant) contain exon A, whereas kidney, stomach, and skeletal muscle tissues comprise NCX with exon B (2-5).Equilibrium binding studies have shown that isolated CBD1 protein contains two sites with high affinity for Ca ]-dependent regulation by cytosolic Ca 2ϩ in cellular systems, whereas the primary site of CBD2 (CaI) may contribute to the Ca 2ϩ -dependent relief of Na ϩ -dependent inactivation of intact NCX (23-25). Importantly, the segment that undergoes alternative splicing is located solely within the CBD2 domain, meaning that specific domain-domain interactions may shape the regulatory properties of primary Ca 2ϩ sites at CBD1 (16 -20, 24). Fluorescence resonance energy transfer studies demonstrated that CBD domains of NCX can undergo significant conformational changes in the cell within the excitation-contraction coupling (22,27), although dynamic aspects of relevant conformational transitions, as well as the contribution of each specific Ca 2ϩ site to regulatory even...

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“…NCX1 can be inactivated by decreasing intracellular Ca 2+ or increasing intracellular Na + concentrations (Reeves and Condrescu, 2008). Increased levels of PIP 2 eliminate the inactivation (He et al, 2000;Yaradanakul et al, 2007) and He et al (2000) showed that PIP 2 could bind to the endogenous XIP region following putative TM helix 5 (Iwamoto et al, 1999;Reeves and Condrescu, 2008;Ren et al, 2010). Additional indirect mechanisms of PIP 2 -regulation of NCX1 such as effects on trafficking have also been described (Yaradanakul et al, 2007).…”

Section: Sodium-calcium Exchanger (Ncx1)mentioning

confidence: 97%

“…The cardiac Na + -Ca 2+ exchanger NCX1 (Reeves and Condrescu, 2008), a member of the Ca 2+ :cation antiporter (CaCA) family (2.A.19), requires anionic phospholipids for activity (Vemuri and Philipson, 1988). NCX1 exists as a homodimer in the membrane (Ren et al, 2008;John et al, 2011) and recently the structure of a bacterial homolog (NCX from Methanococcus jannaschii, NCX Mj ) was solved (Liao et al, 2012).…”

Section: Sodium-calcium Exchanger (Ncx1)mentioning

confidence: 99%

“…The transporter contains a positively charged carboxy-terminal domain that was highlighted as as a possible PIP 2 binding site (Hilgemann and Ball, 1996) and PIP 2 was found bound to the transporter although no specific site could be identified (Asteggiano et al, 2001). NCX1 can be inactivated by decreasing intracellular Ca 2+ or increasing intracellular Na + concentrations (Reeves and Condrescu, 2008). Increased levels of PIP 2 eliminate the inactivation (He et al, 2000;Yaradanakul et al, 2007) and He et al (2000) showed that PIP 2 could bind to the endogenous XIP region following putative TM helix 5 (Iwamoto et al, 1999;Reeves and Condrescu, 2008;Ren et al, 2010).…”

Section: Sodium-calcium Exchanger (Ncx1)mentioning

confidence: 99%

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Influence of lipids on protein-mediated transmembrane transport

Denning

Beckstein

2013

Chemistry and Physics of Lipids

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Transmembrane proteins are responsible for transporting ions and small molecules across the hydrophobic region of the cell membrane. We are reviewing the evidence for regulation of these transport processes by interactions with the lipids of the membrane. We focus on ion channels, including potassium channels, mechanosensitive and pentameric ligand gated ion channels, and active transporters, including pumps, sodium or proton driven secondary transporters and ABC transporters. For ion channels it has been convincingly shown that specific lipid-protein interactions can directly affect their function. In some cases, a combined approach of molecular and structural biology together with computer simulations has revealed the molecular mechanisms. There are also many transporters whose activity depends on lipids but understanding of the molecular mechanisms is only beginning.

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Ionic regulation of the cardiac sodium-calcium exchanger

Cited by 32 publications

References 63 publications

Ca2+ Binding Alters the Interdomain Flexibility between the Two Cytoplasmic Calcium-binding Domains in the Na+/Ca2+ Exchanger

Ca2+ Binding Alters the Interdomain Flexibility between the Two Cytoplasmic Calcium-binding Domains in the Na+/Ca2+ Exchanger

Essential Role of the CBD1-CBD2 Linker in Slow Dissociation of Ca2+ from the Regulatory Two-domain Tandem of NCX1

Influence of lipids on protein-mediated transmembrane transport

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