Proton-sensing Ca2+ Binding Domains Regulate the Cardiac Na+/Ca2+ Exchanger

Boyman, Liron; Hagen, Brian M.; Giladi, Moshe; Hiller, Reuben; Lederer, W. Jonathan; Khananshvili, Daniel

doi:10.1074/jbc.m110.214106

Cited by 59 publications

(80 citation statements)

References 47 publications

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“…For example, ATP depletion causes a significant decrease in cardiac NCX activity (19,20,30,31), and lactate accumulation not only increases cytosolic NADH but also mediates acidosis. Decreased pH inhibits NCX activity (32), which is fully reversible after pH normalization (33). In our study, acidosis is not expected to contribute to the observed lactate-or NADH-mediated I NCX inhibition because cytosolic pH was buffered by dialysis with the pipette solution containing 10 mM HEPES at pH 7.25.…”

Section: Discussionmentioning

confidence: 91%

Regulation of the Na+/Ca2+ Exchanger by Pyridine Nucleotide Redox Potential in Ventricular Myocytes

Liu

O’Rourke

2013

Journal of Biological Chemistry

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Background: Regulation of the sarcolemmal Na ϩ /Ca 2ϩ exchanger (NCX) modulates cardiac excitation-contraction coupling, and NCX contributes to ischemia-reperfusion injury. Results: Increased cytosolic NADH inhibits NCX through a ROS-dependent mechanism. Conclusion: Regulation by cytosolic NADH reveals a novel way that NCX responds to changes in energy metabolism. Significance: NADH-dependent regulation of NCX regulation represents a potential therapeutic target for ameliorating ischemia-reperfusion injury or chronic cardiovascular disease.

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Section: Discussionmentioning

confidence: 91%

Regulation of the Na+/Ca2+ Exchanger by Pyridine Nucleotide Redox Potential in Ventricular Myocytes

Liu

O’Rourke

2013

Journal of Biological Chemistry

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“…Equilibrium binding of 45 Ca 2 + to CBD12-1.4 F450G was measured using a protein-ligand ultrafiltration assay [7,12,30]. The F450G mutation results in a notably decreased affinity for Ca 2 + binding at the high-affinity Ca3-Ca4 sites, displaying affinities similar to those observed for isolated CBD1 ( Figure 3E, Table 1) [7,15].…”

Section: The F450g Mutation Uncouples the Two-domain Interactions In mentioning

confidence: 92%

Structure-dynamic determinants governing a mode of regulatory response and propagation of allosteric signal in splice variants of Na+/Ca2+ exchange (NCX) proteins

Giladi

Lee

Hiller

et al. 2015

Biochemical Journal

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The Ca(2+)-dependent allosteric regulation of Na(+)/Ca(2+) exchanger (NCX) proteins represents Ca(2+) interaction with the cytosolic domains, CBD1 (calcium-binding domain 1) and CBD2, which is associated either with activation, inhibition or no response to regulatory Ca(2+) in a given splice variant. CBD1 contains a high affinity Ca(2+)-sensor (which is highly conserved among splice variants), whereas primary information upon Ca(2+) binding to CBD1 is modified by alternative splicing of CBD2, yielding the diverse regulatory responses to Ca(2+). To resolve the structure-dynamic determinants of splicing-dependent regulation, we tested two-domain tandem (CBD12) constructs possessing either positive, negative or no response to Ca(2+) using hydrogen-deuterium exchange MS (HDX-MS), SAXS, equilibrium 45Ca(2+) binding and stopped-flow kinetics. Taken together with previously resolved crystallographic structures of CBD12, the data revealed that Ca(2+) binding to CBD1 rigidifies the main-chain flexibility of CBD2 (but not of CBD1), whereas CBD2 stabilizes the apo-CBD1. Strikingly, the extent and strength of Ca(2+)-dependent rigidification of CBD2 is splice-variant dependent, where the main-chain rigidification spans from the Ca(2+)-binding sites of CBD1, through a helix of CBD2 (positioned at the domains' interface) up to the tip of CBD2 [>50 Å (1 Å = 0.1 nm)] or alternatively, it stops at the CBD2 helix in the splice variant exhibiting an inhibitory response to regulatory Ca(2+). These results provide a structure-dynamic basis by which alternative splicing diversifies the regulatory responses to Ca(2+) as well as controls the extent and strength of allosteric signal propagation over long distance.

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“…Time constants of allosteric NCX1 activation have been measured in the range of 0.1–10 s in membrane patches [10, 14–17] and additional studies using caffeine application [18–20] or flash-photolysis [21, 22] to generate rapid elevation of [Ca 2+ ] I demonstrated rapid activation of NCX1 by [Ca 2+ ] i . The Ca 2+ half-activation concentration (K mAct ) has been measured in the range of 25–600 nM in both membrane patches and intact cardiomyocytes [17, 18, 23–26]. Ottolia et al [27] observed beat-to-beat conformational changes in CBD12 by measuring fluorescent resonance energy transfer in response to changes of [Ca 2+ ] i in cardiomyocytes, but how these changes in CBD12 conformation lead to NCX1 activation remains unclear.…”

Section: Introductionmentioning

confidence: 99%

Modeling Na + -Ca 2+ exchange in the heart: Allosteric activation, spatial localization, sparks and excitation-contraction coupling

Chu

Greenstein

Winslow

2016

Journal of Molecular and Cellular Cardiology

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The cardiac sodium (Na+)/calcium (Ca2+) exchanger (NCX1) is an electrogenic membrane transporter that regulates Ca2+ homeostasis in cardiomyocytes, serving mainly to extrude Ca2+ during diastole. The direction of Ca2+ transport reverses at membrane potentials near that of the action potential plateau, generating an influx of Ca2+ into the cell. Therefore, there has been great interest in the possible roles of NCX1 in cardiac Ca2+-induced Ca2+ release (CICR). Interest has been reinvigorated by a recent super-resolution optical imaging study suggesting that ~18% of NCX1 co-localize with ryanodine receptor (RyR2) clusters, and ~30% of additional NCX1 are localized to within ~120 nm of the nearest RyR2. NCX1 may therefore occupy a privileged position in which to modulate CICR. To examine this question, we have developed a mechanistic biophysically-detailed model of NCX1 that describes both NCX1 transport kinetics and Ca2+-dependent allosteric regulation. This NCX1 model was incorporated into a previously developed super-resolution model of the Ca2+ spark as well as a computational model of the cardiac ventricular myocyte that includes a detailed description of CICR with stochastic gating of L-type Ca2+ channels and RyR2s, and that accounts for local Ca2+ gradients near the dyad via inclusion of a peri-dyadic (PD) compartment. Both models predict that increasing the fraction of NCX1 in the dyad and PD decreases spark frequency, fidelity, and diastolic Ca2+ levels. Spark amplitude and duration are less sensitive to NCX1 spatial redistribution. On the other hand, NCX1 plays an important role in promoting Ca2+ entry into the dyad, and hence contributing to the trigger for RyR2 release at depolarized membrane potentials and in the presence of elevated local Na+ concentration. Whole-cell simulation of NCX1 tail currents are consistent with the finding that a relatively high fraction of NCX1 (~45%) resides in the dyadic and PD spaces, with a dyad-to-PD ratio of roughly 1:2. Allosteric Ca2+ activation of NCX1 helps to “functionally localize” exchanger activity to the dyad and PD by reducing exchanger activity in the cytosol thereby protecting the cell from excessive loss of Ca2+ during diastole.

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Proton-sensing Ca2+ Binding Domains Regulate the Cardiac Na+/Ca2+ Exchanger

Abstract: This work reveals for the first time that NCX can be switched off by physiologically relevant intracellular acidification and that this depends on the competitive binding of protons to its C 2 regulatory domains CBD1 and CBD2.

Cited by 59 publications

References 47 publications

Regulation of the Na+/Ca2+ Exchanger by Pyridine Nucleotide Redox Potential in Ventricular Myocytes

Regulation of the Na+/Ca2+ Exchanger by Pyridine Nucleotide Redox Potential in Ventricular Myocytes

Structure-dynamic determinants governing a mode of regulatory response and propagation of allosteric signal in splice variants of Na+/Ca2+ exchange (NCX) proteins

Modeling Na + -Ca 2+ exchange in the heart: Allosteric activation, spatial localization, sparks and excitation-contraction coupling

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