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Šeflová J, Cruz-Cortés C, Guerrero-Serna G, Robia SL, Espinoza-Fonseca LM. Mechanisms for cardiac calcium pump activation by its substrate and a synthetic allosteric modulator using fluorescence lifetime imaging. PNAS NEXUS 2024; 3:pgad453. [PMID: 38222469 PMCID: PMC10785037 DOI: 10.1093/pnasnexus/pgad453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/20/2023] [Accepted: 12/15/2023] [Indexed: 01/16/2024]
Abstract
The discovery of allosteric modulators is an emerging paradigm in drug discovery, and signal transduction is a subtle and dynamic process that is challenging to characterize. We developed a time-correlated single photon-counting imaging approach to investigate the structural mechanisms for small-molecule activation of the cardiac sarcoplasmic reticulum Ca2+-ATPase, a pharmacologically important pump that transports Ca2+ at the expense of adenosine triphosphate (ATP) hydrolysis. We first tested whether the dissociation of sarcoplasmic reticulum Ca2+-ATPase from its regulatory protein phospholamban is required for small-molecule activation. We found that CDN1163, a validated sarcoplasmic reticulum Ca2+-ATPase activator, does not have significant effects on the stability of the sarcoplasmic reticulum Ca2+-ATPase-phospholamban complex. Time-correlated single photon-counting imaging experiments using the nonhydrolyzable ATP analog β,γ-Methyleneadenosine 5'-triphosphate (AMP-PCP) showed ATP is an allosteric modulator of sarcoplasmic reticulum Ca2+-ATPase, increasing the fraction of catalytically competent structures at physiologically relevant Ca2+ concentrations. Unlike ATP, CDN1163 alone has no significant effects on the Ca2+-dependent shifts in the structural populations of sarcoplasmic reticulum Ca2+-ATPase, and it does not increase the pump's affinity for Ca2+ ions. However, we found that CDN1163 enhances the ATP-mediated modulatory effects to increase the population of catalytically competent sarcoplasmic reticulum Ca2+-ATPase structures. Importantly, this structural shift occurs within the physiological window of Ca2+ concentrations at which sarcoplasmic reticulum Ca2+-ATPase operates. We demonstrated that ATP is both a substrate and modulator of sarcoplasmic reticulum Ca2+-ATPase and showed that CDN1163 and ATP act synergistically to populate sarcoplasmic reticulum Ca2+-ATPase structures that are primed for phosphorylation. This study provides novel insights into the structural mechanisms for sarcoplasmic reticulum Ca2+-ATPase activation by its substrate and a synthetic allosteric modulator.
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Affiliation(s)
- Jaroslava Šeflová
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL 60153, USA
| | - Carlos Cruz-Cortés
- Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, MI 48109, USA
| | - Guadalupe Guerrero-Serna
- Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, MI 48109, USA
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL 60153, USA
| | - L Michel Espinoza-Fonseca
- Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, MI 48109, USA
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Gorski PA, Lee A, Lee P, Oh JG, Vangheluwe P, Ishikawa K, Hajjar R, Kho C. Identification and Characterization of p300-Mediated Lysine Residues in Cardiac SERCA2a. Int J Mol Sci 2023; 24:ijms24043502. [PMID: 36834924 PMCID: PMC9959367 DOI: 10.3390/ijms24043502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 02/07/2023] [Accepted: 02/07/2023] [Indexed: 02/12/2023] Open
Abstract
Impaired calcium uptake resulting from reduced expression and activity of the cardiac sarco-endoplasmic reticulum Ca2+ ATPase (SERCA2a) is a hallmark of heart failure (HF). Recently, new mechanisms of SERCA2a regulation, including post-translational modifications (PTMs), have emerged. Our latest analysis of SERCA2a PTMs has identified lysine acetylation as another PTM which might play a significant role in regulating SERCA2a activity. SERCA2a is acetylated, and that acetylation is more prominent in failing human hearts. In this study, we confirmed that p300 interacts with and acetylates SERCA2a in cardiac tissues. Several lysine residues in SERCA2a modulated by p300 were identified using in vitro acetylation assay. Analysis of in vitro acetylated SERCA2a revealed several lysine residues in SERCA2a susceptible to acetylation by p300. Among them, SERCA2a Lys514 (K514) was confirmed to be essential for SERCA2a activity and stability using an acetylated mimicking mutant. Finally, the reintroduction of an acetyl-mimicking mutant of SERCA2a (K514Q) into SERCA2 knockout cardiomyocytes resulted in deteriorated cardiomyocyte function. Taken together, our data demonstrated that p300-mediated acetylation of SERCA2a is a critical PTM that decreases the pump's function and contributes to cardiac impairment in HF. SERCA2a acetylation can be targeted for therapeutic aims for the treatment of HF.
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Affiliation(s)
- Przemek A. Gorski
- Cardiovascular Research Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Ahyoung Lee
- Research Institute for Korean Medicine, Pusan National University, Yangsan 50612, Republic of Korea
| | - Philyoung Lee
- New Drug Development Center, Osong Medical Innovation Fundation, Osong, Seoul 02841, Republic of Korea
| | - Jae Gyun Oh
- Cardiovascular Research Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Peter Vangheluwe
- Department of Cellular and Molecular Medicine, KU Leuven, 3000 Leuven, Belgium
| | - Kiyotake Ishikawa
- Cardiovascular Research Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Roger Hajjar
- Phospholamban Foundation, 1775 ZH Amsterdam, The Netherlands
| | - Changwon Kho
- Division of Applied Medicine, School of Korean Medicine, Pusan National University, Yangsan 50612, Republic of Korea
- Correspondence: ; Tel.: +82-51-510-8467
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Chambers PJ, Juracic ES, Fajardo VA, Tupling AR. The role of SERCA and sarcolipin in adaptive muscle remodeling. Am J Physiol Cell Physiol 2022; 322:C382-C394. [PMID: 35044855 DOI: 10.1152/ajpcell.00198.2021] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Sarcolipin (SLN) is a small integral membrane protein that regulates the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) pump. When bound to SERCA, SLN reduces the apparent Ca2+ affinity of SERCA and uncouples SERCA Ca2+ transport from its ATP consumption. As such, SLN plays a direct role in altering skeletal muscle relaxation and energy expenditure. Interestingly, the expression of SLN is dynamic during times of muscle adaptation, where large increases in SLN content are found in response to development, atrophy, overload and disease. Several groups have suggested that increases in SLN, especially in dystrophic muscle, are deleterious to muscle function and exacerbate already abhorrent intracellular Ca2+ levels. However, there is also significant evidence to show that increased SLN content is a beneficial adaptive mechanism which protects the SERCA pump and activates Ca2+ signaling and adaptive remodeling during times of cell stress. In this review, we first discuss the role for SLN in healthy muscle during both development and overload, where SLN has been shown to activate Ca2+ signaling to promote mitochondrial biogenesis, fibre type shifts and muscle hypertrophy. Then, with respect to muscle disease, we summarize the discrepancies in the literature as to whether SLN upregulation is adaptive or maladaptive in nature. This review is the first to offer the concept of SLN hormesis in muscle disease, wherein both too much and too little SLN are detrimental to muscle health. Finally, the underlying mechanisms which activate SLN upregulation are discussed, specifically acknowledging a potential positive feedback loop between SLN and Ca2+ signaling molecules.
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Affiliation(s)
- Paige J Chambers
- Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
| | - Emma S Juracic
- Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
| | - Val A Fajardo
- Department Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada.,Centre for Bone and Muscle Health, Brock University, St. Catharines, Ontario, Canada
| | - A Russell Tupling
- Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
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Alford RF, Smolin N, Young HS, Gray JJ, Robia SL. Protein docking and steered molecular dynamics suggest alternative phospholamban-binding sites on the SERCA calcium transporter. J Biol Chem 2020; 295:11262-11274. [PMID: 32554805 DOI: 10.1074/jbc.ra120.012948] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 06/16/2020] [Indexed: 01/27/2023] Open
Abstract
The transport activity of the sarco(endo)plasmic reticulum calcium ATPase (SERCA) in cardiac myocytes is modulated by an inhibitory interaction with a transmembrane peptide, phospholamban (PLB). Previous biochemical studies have revealed that PLB interacts with a specific inhibitory site on SERCA, and low-resolution structural evidence suggests that PLB interacts with distinct alternative sites on SERCA. High-resolution details of the structural determinants of SERCA regulation have been elusive because of the dynamic nature of the regulatory complex. In this study, we used computational approaches to develop a structural model of SERCA-PLB interactions to gain a mechanistic understanding of PLB-mediated SERCA transport regulation. We combined steered molecular dynamics and membrane protein-protein docking experiments to achieve both a global search and all-atom force calculations to determine the relative affinities of PLB for candidate sites on SERCA. We modeled the binding of PLB to several SERCA conformations, representing different enzymatic states sampled during the calcium transport catalytic cycle. The results of the steered molecular dynamics and docking experiments indicated that the canonical PLB-binding site (comprising transmembrane helices M2, M4, and M9) is the preferred site. This preference was even more stringent for a superinhibitory PLB variant. Interestingly, PLB-binding specificity became more ambivalent for other SERCA conformers. These results provide evidence for polymorphic PLB interactions with novel sites on M3 and with the outside of the SERCA helix M9. Our findings are compatible with previous physical measurements that suggest that PLB interacts with multiple binding sites, conferring dynamic responsiveness to changing physiological conditions.
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Affiliation(s)
- Rebecca F Alford
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, USA
| | - Nikolai Smolin
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Cardiovascular Research Institute, Loyola University Chicago, Maywood, Illinois, USA
| | - Howard S Young
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Jeffrey J Gray
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, USA
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Cardiovascular Research Institute, Loyola University Chicago, Maywood, Illinois, USA
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Association with SERCA2a directs phospholamban trafficking to sarcoplasmic reticulum from a nuclear envelope pool. J Mol Cell Cardiol 2020; 143:107-119. [DOI: 10.1016/j.yjmcc.2020.04.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 04/08/2020] [Accepted: 04/23/2020] [Indexed: 11/22/2022]
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Glaves JP, Primeau JO, Espinoza-Fonseca LM, Lemieux MJ, Young HS. The Phospholamban Pentamer Alters Function of the Sarcoplasmic Reticulum Calcium Pump SERCA. Biophys J 2019; 116:633-647. [PMID: 30712785 DOI: 10.1016/j.bpj.2019.01.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 11/30/2018] [Accepted: 01/11/2019] [Indexed: 11/17/2022] Open
Abstract
The interaction of phospholamban (PLN) with the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) pump is a major regulatory axis in cardiac muscle contractility. The prevailing model involves reversible inhibition of SERCA by monomeric PLN and storage of PLN as an inactive pentamer. However, this paradigm has been challenged by studies demonstrating that PLN remains associated with SERCA and that the PLN pentamer is required for the regulation of cardiac contractility. We have previously used two-dimensional (2D) crystallization and electron microscopy to study the interaction between SERCA and PLN. To further understand this interaction, we compared small helical crystals and large 2D crystals of SERCA in the absence and presence of PLN. In both crystal forms, SERCA molecules are organized into identical antiparallel dimer ribbons. The dimer ribbons pack together with distinct crystal contacts in the helical versus large 2D crystals, which allow PLN differential access to potential sites of interaction with SERCA. Nonetheless, we show that a PLN oligomer interacts with SERCA in a similar manner in both crystal forms. In the 2D crystals, a PLN pentamer interacts with transmembrane segments M3 of SERCA and participates in a crystal contact that bridges neighboring SERCA dimer ribbons. In the helical crystals, an oligomeric form of PLN also interacts with M3 of SERCA, though the PLN oligomer straddles a SERCA-SERCA crystal contact. We conclude that the pentameric form of PLN interacts with M3 of SERCA and that it plays a distinct structural and functional role in SERCA regulation. The interaction of the pentamer places the cytoplasmic domains of PLN at the membrane surface proximal to the calcium entry funnel of SERCA. This interaction may cause localized perturbation of the membrane bilayer as a mechanism for increasing the turnover rate of SERCA.
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Affiliation(s)
- John Paul Glaves
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Joseph O Primeau
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - L Michel Espinoza-Fonseca
- Center for Arrhythmia Research, Division of Cardiovascular Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
| | - M Joanne Lemieux
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Howard S Young
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada.
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Chen M, Xu D, Wu AZ, Kranias E, Lin SF, Chen PS, Chen Z. Phospholamban regulates nuclear Ca 2+ stores and inositol 1,4,5-trisphosphate mediated nuclear Ca 2+ cycling in cardiomyocytes. J Mol Cell Cardiol 2018; 123:185-197. [PMID: 30261161 DOI: 10.1016/j.yjmcc.2018.09.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 09/04/2018] [Accepted: 09/21/2018] [Indexed: 01/15/2023]
Abstract
AIMS Phospholamban (PLB) is the key regulator of the cardiac Ca2+ pump (SERCA2a)-mediated sarcoplasmic reticulum Ca2+ stores. We recently reported that PLB is highly concentrated in the nuclear envelope (NE) from where it can modulate perinuclear Ca2+ handling of the cardiomyocytes (CMs). Since inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) mediates nuclear Ca2+ release, we examined whether the nuclear pool of PLB regulates IP3-induced nuclear Ca2+ handling. METHODS AND RESULTS Fluo-4 based confocal Ca2+ imaging was performed to measure Ca2+ dynamics across both nucleus and cytosol in saponin-permeabilized CMs isolated from wild-type (WT) or PLB-knockout (PLB-KO) mice. At diastolic intracellular Ca2+ ([Ca2+]i = 100 nM), the Fab fragment of the monoclonal PLB antibody (anti-PLB Fab) facilitated the formation and increased the length of spontaneous Ca2+ waves (SCWs) originating from the nuclear region in CMs from WT but not from PLB-KO mice. We next examined nuclear Ca2+ activities at basal condition and after sequential addition of IP3, anti-PLB Fab, and the IP3R inhibitor 2-aminoethoxydiphenyl borate (2-APB) at a series of [Ca2+]i. In WT mice, at 10 nM [Ca2+]i where ryanodine receptor (RyR2) based spontaneous Ca2+ sparks rarely occurred, IP3 increased fluorescence amplitude (F/F0) of overall nuclear region to 1.19 ± 0.02. Subsequent addition of anti-PLB Fab significantly decreased F/F0 to 1.09 ± 0.02. At 50 nM [Ca2+]i, anti-PLB Fab not only decreased the overall nuclear F/F0 previously elevated by IP3, but also increased the amplitude and duration of spark-like nuclear Ca2+ release events. These nuclear Ca2+ releases were blocked by 2-APB. At 100 nM [Ca2+]i, IP3 induced short SCWs originating from nucleus. Anti-PLB Fab transformed those short waves into long SCWs with propagation from the nucleus into the cytosol. In contrast, neither nuclear nor cytosolic Ca2+ dynamics was affected by anti-PLB Fab in CMs from PLB-KO mice in all these conditions. Furthermore, in WT CMs pretreated with RyR2 blocker tetracaine, IP3 and anti-PLB Fab still increased the magnitude of nuclear Ca2+ release but failed to regenerate SCWs. Finally, anti-PLB Fab increased low Ca2+ affinity mag-fluo 4 fluorescence intensity in the lumen of NE of nuclei isolated from WT but not in PLB-KO mice. CONCLUSION PLB regulates nuclear Ca2+ handling. By increasing Ca2+ uptake into lumen of the NE and perhaps other perinuclear membranes, the acute reversal of PLB inhibition decreases global Ca2+ concentration at rest in the nucleoplasm, and increases Ca2+ release into the nucleus, through mechanisms involving IP3R and RyR2 in the vicinity.
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Affiliation(s)
- Mu Chen
- Krannert Institute of Cardiology, Indiana University, Indianapolis, IN, USA; Department of Cardiology, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Dongzhu Xu
- Krannert Institute of Cardiology, Indiana University, Indianapolis, IN, USA; Cardiovascular Division, Institute of Clinical Medicine, Faculty of Medicine, University of Tsukuba, Japan
| | - Adonis Z Wu
- Krannert Institute of Cardiology, Indiana University, Indianapolis, IN, USA
| | - Evangelia Kranias
- Department of Pharmacology and Systems Physiology, University of Cincinnati College of Medicine, Cincinnati, OH, USA
| | - Shien-Fong Lin
- Krannert Institute of Cardiology, Indiana University, Indianapolis, IN, USA; Institute of Biomedical Engineering, College of Electrical and Computer Engineering, National Chiao Tung University, Hsin-Chu, Taiwan
| | - Peng-Sheng Chen
- Krannert Institute of Cardiology, Indiana University, Indianapolis, IN, USA
| | - Zhenhui Chen
- Krannert Institute of Cardiology, Indiana University, Indianapolis, IN, USA.
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Vinogradova TM, Tagirova Sirenko S, Lakatta EG. Unique Ca 2+-Cycling Protein Abundance and Regulation Sustains Local Ca 2+ Releases and Spontaneous Firing of Rabbit Sinoatrial Node Cells. Int J Mol Sci 2018; 19:ijms19082173. [PMID: 30044420 PMCID: PMC6121616 DOI: 10.3390/ijms19082173] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Revised: 07/20/2018] [Accepted: 07/23/2018] [Indexed: 11/16/2022] Open
Abstract
Spontaneous beating of the heart pacemaker, the sinoatrial node, is generated by sinoatrial node cells (SANC) and caused by gradual change of the membrane potential called diastolic depolarization (DD). Submembrane local Ca2+ releases (LCR) from sarcoplasmic reticulum (SR) occur during late DD and activate an inward Na+/Ca2+ exchange current, which accelerates the DD rate leading to earlier occurrence of an action potential. A comparison of intrinsic SR Ca2+ cycling revealed that, at similar physiological Ca2+ concentrations, LCRs are large and rhythmic in permeabilized SANC, but small and random in permeabilized ventricular myocytes (VM). Permeabilized SANC spontaneously released more Ca2+ from SR than VM, despite comparable SR Ca2+ content in both cell types. In this review we discuss specific patterns of expression and distribution of SR Ca2+ cycling proteins (SR Ca2+ ATPase (SERCA2), phospholamban (PLB) and ryanodine receptors (RyR)) in SANC and ventricular myocytes. We link ability of SANC to generate larger and rhythmic LCRs with increased abundance of SERCA2, reduced abundance of the SERCA inhibitor PLB. In addition, an increase in intracellular [Ca2+] increases phosphorylation of both PLB and RyR exclusively in SANC. The differences in SR Ca2+ cycling protein expression between SANC and VM provide insights into diverse regulation of intrinsic SR Ca2+ cycling that drives automaticity of SANC.
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Affiliation(s)
- Tatiana M Vinogradova
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 251 Bayview Blvd, Room 8B-123, Baltimore, MD 21224, USA.
| | - Syevda Tagirova Sirenko
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 251 Bayview Blvd, Room 8B-123, Baltimore, MD 21224, USA.
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, NIH, 251 Bayview Blvd, Room 8B-123, Baltimore, MD 21224, USA.
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Fernández-de Gortari E, Espinoza-Fonseca LM. Structural basis for relief of phospholamban-mediated inhibition of the sarcoplasmic reticulum Ca 2+-ATPase at saturating Ca 2+ conditions. J Biol Chem 2018; 293:12405-12414. [PMID: 29934304 DOI: 10.1074/jbc.ra118.003752] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 06/21/2018] [Indexed: 11/06/2022] Open
Abstract
Sarcoplasmic reticulum Ca2+-ATPase (SERCA) is critical for cardiac Ca2+ transport. Reversal of phospholamban (PLB)-mediated SERCA inhibition by saturating Ca2+ conditions operates as a physiological rheostat to reactivate SERCA function in the absence of PLB phosphorylation. Here, we performed extensive atomistic molecular dynamics simulations to probe the structural mechanism of this process. Simulation of the inhibitory complex at superphysiological Ca2+ concentrations ([Ca2+] = 10 mm) revealed that Ca2+ ions interact primarily with SERCA and the lipid headgroups, but not with PLB's cytosolic domain or the cytosolic side of the SERCA-PLB interface. At this [Ca2+], a single Ca2+ ion was translocated from the cytosol to the transmembrane transport sites. We used this Ca2+-bound complex as an initial structure to simulate the effects of saturating Ca2+ at physiological conditions ([Ca2+]total ≈ 400 μm). At these conditions, ∼30% of the Ca2+-bound complexes exhibited structural features consistent with an inhibited state. However, in ∼70% of the Ca2+-bound complexes, Ca2+ moved to transport site I, recruited Glu771 and Asp800, and disrupted key inhibitory contacts involving the conserved PLB residue Asn34 Structural analysis showed that Ca2+ induces only local changes in interresidue inhibitory interactions, but does not induce repositioning or changes in PLB structural dynamics. Upon relief of SERCA inhibition, Ca2+ binding produced a site I configuration sufficient for subsequent SERCA activation. We propose that at saturating [Ca2+] and in the absence of PLB phosphorylation, binding of a single Ca2+ ion in the transport sites rapidly shifts the equilibrium toward a noninhibited SERCA-PLB complex.
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Affiliation(s)
- Eli Fernández-de Gortari
- From the Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, Michigan 48109
| | - L Michel Espinoza-Fonseca
- From the Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular Medicine, University of Michigan, Ann Arbor, Michigan 48109
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10
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Espinoza-Fonseca LM, Autry JM, Ramírez-Salinas GL, Thomas DD. Atomic-level mechanisms for phospholamban regulation of the calcium pump. Biophys J 2016; 108:1697-1708. [PMID: 25863061 DOI: 10.1016/j.bpj.2015.03.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 02/25/2015] [Accepted: 03/04/2015] [Indexed: 12/29/2022] Open
Abstract
We performed protein pKa calculations and molecular dynamics (MD) simulations of the calcium pump (sarcoplasmic reticulum Ca(2+)-ATPase (SERCA)) in complex with phospholamban (PLB). X-ray crystallography studies have suggested that PLB locks SERCA in a low-Ca(2+)-affinity E2 state that is incompatible with metal-ion binding, thereby blocking the conversion toward a high-Ca(2+)-affinity E1 state. Estimation of pKa values of the acidic residues in the transport sites indicates that at normal intracellular pH (7.1-7.2), PLB-bound SERCA populates an E1 state that is deprotonated at residues E309 and D800 yet protonated at residue E771. We performed three independent microsecond-long MD simulations to evaluate the structural dynamics of SERCA-PLB in a solution containing 100 mM K(+) and 3 mM Mg(2+). Principal component analysis showed that PLB-bound SERCA lies exclusively along the structural ensemble of the E1 state. We found that the transport sites of PLB-bound SERCA are completely exposed to the cytosol and that K(+) ions bind transiently (≤5 ns) and nonspecifically (nine different positions) to the two transport sites, with a total occupancy time of K(+) in the transport sites of 80%. We propose that PLB binding to SERCA populates a novel (to our knowledge) E1 intermediate, E1⋅H(+)771. This intermediate serves as a kinetic trap that controls headpiece dynamics and depresses the structural transitions necessary for Ca(2+)-dependent activation of SERCA. We conclude that PLB-mediated regulation of SERCA activity in the heart results from biochemical and structural transitions that occur primarily in the E1 state of the pump.
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Affiliation(s)
- L Michel Espinoza-Fonseca
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota.
| | - Joseph M Autry
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota
| | - G Lizbeth Ramírez-Salinas
- Laboratorio de Modelado Molecular y Bioinformática, Escuela Superior de Medicina, Instituto Politécnico Nacional, Mexico City, Mexico
| | - David D Thomas
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota
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11
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Chen Z. Role of nucleotides in stabilization of the phospholamban/cardiac Ca²⁺ pump inhibitory complex examined with use of metal fluorides. FEBS J 2015; 282:4402-14. [PMID: 26337774 DOI: 10.1111/febs.13506] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Revised: 08/21/2015] [Accepted: 09/01/2015] [Indexed: 11/29/2022]
Abstract
Phospholamban (PLB) inhibits the activity of the cardiac calcium pump SERCA2a. We previously showed that PLB with engineered Cys residues only cross-linked with the Ca(2+) -free E2 intermediate of SERCA2a. Formation of E2•PLB prevents Ca(2+) binding at the high-affinity Ca(2+) binding sites, blocking the enzyme kinetic cycle. Here we further studied the synergistic action of PLB and ATP on E2 in terms of prevention of formation of the phosphorylated E2P-like states stabilized by metal fluorides. SERCA2a was co-expressed in insect cell microsomes with PLB mutants of normal or super-inhibitory strength, with cross-linkable mutations at either the cytosolic side (N30C) or the luminal side (V49C) of PLB. For normal-strength PLB mutants, in the absence of nucleotide, metal fluorides totally inhibited both SERCA2a enzyme activity and cross-linking of PLB to SERCA2a at both sites, suggesting that PLB dissociates from SERCA2a in the E2P-like states. However, under the same conditions, super-inhibitory PLB mutants prevented total enzyme inhibition by metal fluorides. Further, the cross-linking of super-inhibitory PLB to SERCA2a was only partially inhibited by metal fluorides, but was drastically restored upon sequential addition of ATP. These results revealed the equilibrium between E2•PLB, E2•ATP, or E2•ATP•PLB states and E2P-like states, suggesting that the synergistic binding of ATP and PLB to SERCA is very strong, sufficient to prevent formation of E2 phosphoenzymes, even when stabilized by metal fluorides.
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Affiliation(s)
- Zhenhui Chen
- Krannert Institute of Cardiology and Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, 46202, USA
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12
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Chan YH, Tsai WC, Song Z, Ko CY, Qu Z, Weiss JN, Lin SF, Chen PS, Jones LR, Chen Z. Acute reversal of phospholamban inhibition facilitates the rhythmic whole-cell propagating calcium waves in isolated ventricular myocytes. J Mol Cell Cardiol 2015; 80:126-35. [PMID: 25596331 DOI: 10.1016/j.yjmcc.2014.12.024] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Revised: 12/08/2014] [Accepted: 12/30/2014] [Indexed: 02/01/2023]
Abstract
Phospholamban (PLB) inhibits the activity of cardiac sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA2a). Phosphorylation of PLB during sympathetic activation reverses SERCA2a inhibition, increasing SR Ca(2+) uptake. However, sympathetic activation also modulates multiple other intracellular targets in ventricular myocytes (VMs), making it impossible to determine the specific effects of the reversal of PLB inhibition on the spontaneous SR Ca(2+) release. Therefore, it remains unclear how PLB regulates rhythmic activity in VMs. Here, we used the Fab fragment of 2D12, a monoclonal anti-PLB antibody, to test how acute reversal of PLB inhibition affects the spontaneous SR Ca(2+) release in normal VMs. Ca(2+) sparks and spontaneous Ca(2+) waves (SCWs) were recorded in the line-scan mode of confocal microscopy using the Ca(2+) fluorescent dye Fluo-4 in isolated permeabilized mouse VMs. Fab, which reverses PLB inhibition, significantly increased the frequency, amplitude, and spatial/temporal spread of Ca(2+) sparks in VMs exposed to 50 nM free [Ca(2+)]. At physiological diastolic free [Ca(2+)] (100-200 nM), Fab facilitated the formation of whole-cell propagating SCWs. At higher free [Ca(2+)], Fab increased the frequency and velocity, but decreased the decay time of the SCWs. cAMP had little additional effect on the frequency or morphology of Ca(2+) sparks or SCWs after Fab addition. These findings were complemented by computer simulations. In conclusion, acute reversal of PLB inhibition alone significantly increased the spontaneous SR Ca(2+) release, leading to the facilitation and organization of whole-cell propagating SCWs in normal VMs. PLB thus plays a key role in subcellular Ca(2+) dynamics and rhythmic activity of VMs.
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Affiliation(s)
- Yi-Hsin Chan
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA; Division of Cardiology, Department of Internal Medicine, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Linkou, Taoyuan, Taiwan
| | - Wei-Chung Tsai
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA; Division of Cardiology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung University College of Medicine, Kaohsiung, Taiwan
| | - Zhen Song
- Division of Cardiology, Department of Medicine, University of California, Los Angeles, CA, USA
| | - Christopher Y Ko
- Division of Cardiology, Department of Medicine, University of California, Los Angeles, CA, USA
| | - Zhilin Qu
- Division of Cardiology, Department of Medicine, University of California, Los Angeles, CA, USA
| | - James N Weiss
- Division of Cardiology, Department of Medicine, University of California, Los Angeles, CA, USA
| | - Shien-Fong Lin
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA; Institute of Biomedical Engineering, National Chiao-Tung University, Hsin-Chu, Taiwan
| | - Peng-Sheng Chen
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Larry R Jones
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Zhenhui Chen
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
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13
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Chen Z. Competitive displacement of wild-type phospholamban from the Ca2+-free cardiac calcium pump by phospholamban mutants with different binding affinities. J Mol Cell Cardiol 2014; 76:130-7. [DOI: 10.1016/j.yjmcc.2014.08.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2014] [Revised: 08/08/2014] [Accepted: 08/25/2014] [Indexed: 11/29/2022]
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14
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Ablorh NAD, Dong X, James ZM, Xiong Q, Zhang J, Thomas DD, Karim CB. Synthetic phosphopeptides enable quantitation of the content and function of the four phosphorylation states of phospholamban in cardiac muscle. J Biol Chem 2014; 289:29397-405. [PMID: 25190804 DOI: 10.1074/jbc.m114.556621] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have studied the differential effects of phospholamban (PLB) phosphorylation states on the activity of the sarcoplasmic reticulum Ca-ATPase (SERCA). It has been shown that unphosphorylated PLB (U-PLB) inhibits SERCA and that phosphorylation of PLB at Ser-16 or Thr-17 relieves this inhibition in cardiac sarcoplasmic reticulum. However, the levels of the four phosphorylation states of PLB (U-PLB, P16-PLB, P17-PLB, and doubly phosphorylated 2P-PLB) have not been measured quantitatively in cardiac tissue, and their functional effects on SERCA have not been determined directly. We have solved both problems through the chemical synthesis of all four PLB species. We first used the synthetic PLB as standards for a quantitative immunoblot assay, to determine the concentrations of all four PLB phosphorylation states in pig cardiac tissue, with and without left ventricular hypertrophy (LVH) induced by aortic banding. In both LVH and sham hearts, all phosphorylation states were significantly populated, but LVH hearts showed a significant decrease in U-PLB, with a corresponding increase in the ratio of total phosphorylated PLB to U-PLB. To determine directly the functional effects of each PLB species, we co-reconstituted each of the synthetic peptides in phospholipid membranes with SERCA and measured calcium-dependent ATPase activity. SERCA inhibition was maximally relieved by P16-PLB (the most highly populated PLB state in cardiac tissue homogenates), followed by 2P-PLB, then P17-PLB. These results show that each PLB phosphorylation state uniquely alters Ca(2+) homeostasis, with important implications for cardiac health, disease, and therapy.
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Affiliation(s)
| | - Xiaoqiong Dong
- From the Departments of Biochemistry, Molecular Biology and Biophysics and
| | - Zachary M James
- From the Departments of Biochemistry, Molecular Biology and Biophysics and
| | - Qiang Xiong
- Medicine, University of Minnesota, Minneapolis, Minnesota 55455
| | - Jianyi Zhang
- Medicine, University of Minnesota, Minneapolis, Minnesota 55455
| | - David D Thomas
- From the Departments of Biochemistry, Molecular Biology and Biophysics and
| | - Christine B Karim
- From the Departments of Biochemistry, Molecular Biology and Biophysics and
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15
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Stern MD, Maltseva LA, Juhaszova M, Sollott SJ, Lakatta EG, Maltsev VA. Hierarchical clustering of ryanodine receptors enables emergence of a calcium clock in sinoatrial node cells. J Gen Physiol 2014; 143:577-604. [PMID: 24778430 PMCID: PMC4003189 DOI: 10.1085/jgp.201311123] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Accepted: 04/07/2014] [Indexed: 12/12/2022] Open
Abstract
The sinoatrial node, whose cells (sinoatrial node cells [SANCs]) generate rhythmic action potentials, is the primary pacemaker of the heart. During diastole, calcium released from the sarcoplasmic reticulum (SR) via ryanodine receptors (RyRs) interacts with membrane currents to control the rate of the heartbeat. This "calcium clock" takes the form of stochastic, partially periodic, localized calcium release (LCR) events that propagate, wave-like, for limited distances. The detailed mechanisms controlling the calcium clock are not understood. We constructed a computational model of SANCs, including three-dimensional diffusion and buffering of calcium in the cytosol and SR; explicit, stochastic gating of individual RyRs and L-type calcium channels; and a full complement of voltage- and calcium-dependent membrane currents. We did not include an anatomical submembrane space or inactivation of RyRs, the two heuristic components that have been used in prior models but are not observed experimentally. When RyRs were distributed in discrete clusters separated by >1 µm, only isolated sparks were produced in this model and LCR events did not form. However, immunofluorescent staining of SANCs for RyR revealed the presence of bridging RyR groups between large clusters, forming an irregular network. Incorporation of this architecture into the model led to the generation of propagating LCR events. Partial periodicity emerged from the interaction of LCR events, as observed experimentally. This calcium clock becomes entrained with membrane currents to accelerate the beating rate, which therefore was controlled by the activity of the SERCA pump, RyR sensitivity, and L-type current amplitude, all of which are targets of β-adrenergic-mediated phosphorylation. Unexpectedly, simulations revealed the existence of a pathological mode at high RyR sensitivity to calcium, in which the calcium clock loses synchronization with the membrane, resulting in a paradoxical decrease in beating rate in response to β-adrenergic stimulation. The model indicates that the hierarchical clustering of surface RyRs in SANCs may be a crucial adaptive mechanism. Pathological desynchronization of the clocks may explain sinus node dysfunction in heart failure and RyR mutations.
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Affiliation(s)
- Michael D Stern
- Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224
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16
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Yu X, Lorigan GA. Secondary structure, backbone dynamics, and structural topology of phospholamban and its phosphorylated and Arg9Cys-mutated forms in phospholipid bilayers utilizing 13C and 15N solid-state NMR spectroscopy. J Phys Chem B 2014; 118:2124-33. [PMID: 24511878 PMCID: PMC3983341 DOI: 10.1021/jp500316s] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Phospholamban (PLB) is a membrane protein that regulates heart muscle relaxation rates via interactions with the sarcoplasmic reticulum Ca(2+) ATPase (SERCA). When PLB is phosphorylated or Arg9Cys (R9C) is mutated, inhibition of SERCA is relieved. (13)C and (15)N solid-state NMR spectroscopy is utilized to investigate conformational changes of PLB upon phosphorylation and R9C mutation. (13)C═O NMR spectra of the cytoplasmic domain reveal two α-helical structural components with population changes upon phosphorylation and R9C mutation. The appearance of an unstructured component is observed on domain Ib. (15)N NMR spectra indicate an increase in backbone dynamics of the cytoplasmic domain. Wild-type PLB (WT-PLB), Ser16-phosphorylated PLB (P-PLB), and R9C-mutated PLB (R9C-PLB) all have a very dynamic domain Ib, and the transmembrane domain has an immobile component. (15)N NMR spectra indicate that the cytoplasmic domain of R9C-PLB adopts an orientation similar to P-PLB and shifts away from the membrane surface. Domain Ib (Leu28) of P-PLB and R9C-PLB loses the alignment. The R9C-PLB adopts a conformation similar to P-PLB with a population shift to a more extended and disordered state. The NMR data suggest the more extended and disordered forms of PLB may relate to inhibition relief.
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Affiliation(s)
- Xueting Yu
- Department of Chemistry and Biochemistry, Miami University , Oxford, Ohio 45056, United States
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17
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Sirenko S, Maltsev VA, Maltseva LA, Yang D, Lukyanenko Y, Vinogradova TM, Jones LR, Lakatta EG. Sarcoplasmic reticulum Ca2+ cycling protein phosphorylation in a physiologic Ca2+ milieu unleashes a high-power, rhythmic Ca2+ clock in ventricular myocytes: relevance to arrhythmias and bio-pacemaker design. J Mol Cell Cardiol 2014; 66:106-15. [PMID: 24274954 PMCID: PMC3896924 DOI: 10.1016/j.yjmcc.2013.11.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2013] [Revised: 11/07/2013] [Accepted: 11/14/2013] [Indexed: 10/26/2022]
Abstract
Basal phosphorylation of sarcoplasmic reticulum (SR) Ca(2+) proteins is high in sinoatrial nodal cells (SANC), which generate partially synchronized, spontaneous, rhythmic, diastolic local Ca(2+) releases (LCRs), but low in ventricular myocytes (VM), which exhibit rare diastolic, stochastic SR-generated Ca(2+) sparks. We tested the hypothesis that in a physiologic Ca(2+) milieu, and independent of increased Ca(2+) influx, an increase in basal phosphorylation of SR Ca(2+) cycling proteins will convert stochastic Ca(2+) sparks into periodic, high-power Ca(2+) signals of the type that drives SANC normal automaticity. We measured phosphorylation of SR-associated proteins, phospholamban (PLB) and ryanodine receptors (RyR), and spontaneous local Ca(2+) release characteristics (LCR) in permeabilized single, rabbit VM in physiologic [Ca(2+)], prior to and during inhibition of protein phosphatase (PP) and phosphodiesterase (PDE), or addition of exogenous cAMP, or in the presence of an antibody (2D12), that specifically inhibits binding of the PLB to SERCA-2. In the absence of the aforementioned perturbations, VM could only generate stochastic local Ca(2+) releases of low power and low amplitude, as assessed by confocal Ca(2+) imaging and spectral analysis. When the kinetics of Ca(2+) pumping into the SR were increased by an increase in PLB phosphorylation (via PDE and PP inhibition or addition of cAMP) or by 2D12, self-organized, "clock-like" local Ca(2+) releases, partially synchronized in space and time (Ca(2+) wavelets), emerged, and the ensemble of these rhythmic local Ca(2+) wavelets generated a periodic high-amplitude Ca(2+) signal. Thus, a Ca(2+) clock is not specific to pacemaker cells, but can also be unleashed in VM when SR Ca(2+) cycling increases and spontaneous local Ca(2+) release becomes partially synchronized. This unleashed Ca(2+) clock that emerges in a physiological Ca(2+) milieu in VM has two faces, however: it can provoke ventricular arrhythmias; or if harnessed, can be an important feature of novel bio-pacemaker designs.
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Affiliation(s)
- Syevda Sirenko
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Victor A Maltsev
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Larissa A Maltseva
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Dongmei Yang
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Yevgeniya Lukyanenko
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Tatiana M Vinogradova
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA
| | - Larry R Jones
- Department of Medicine, Krannert Institute of Cardiology, Indianapolis, IN, USA
| | - Edward G Lakatta
- Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD, USA.
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18
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Akin BL, Hurley TD, Chen Z, Jones LR. The structural basis for phospholamban inhibition of the calcium pump in sarcoplasmic reticulum. J Biol Chem 2013; 288:30181-30191. [PMID: 23996003 DOI: 10.1074/jbc.m113.501585] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
P-type ATPases are a large family of enzymes that actively transport ions across biological membranes by interconverting between high (E1) and low (E2) ion-affinity states; these transmembrane transporters carry out critical processes in nearly all forms of life. In striated muscle, the archetype P-type ATPase, SERCA (sarco(endo)plasmic reticulum Ca(2+)-ATPase), pumps contractile-dependent Ca(2+) ions into the lumen of sarcoplasmic reticulum, which initiates myocyte relaxation and refills the sarcoplasmic reticulum in preparation for the next contraction. In cardiac muscle, SERCA is regulated by phospholamban (PLB), a small inhibitory phosphoprotein that decreases the Ca(2+) affinity of SERCA and attenuates contractile strength. cAMP-dependent phosphorylation of PLB reverses Ca(2+)-ATPase inhibition with powerful contractile effects. Here we present the long sought crystal structure of the PLB-SERCA complex at 2.8-Å resolution. The structure was solved in the absence of Ca(2+) in a novel detergent system employing alkyl mannosides. The structure shows PLB bound to a previously undescribed conformation of SERCA in which the Ca(2+) binding sites are collapsed and devoid of divalent cations (E2-PLB). This new structure represents one of the key unsolved conformational states of SERCA and provides a structural explanation for how dephosphorylated PLB decreases Ca(2+) affinity and depresses cardiac contractility.
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Affiliation(s)
- Brandy L Akin
- From the Krannert Institute of Cardiology and the Departments of Medicine and.
| | - Thomas D Hurley
- Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202
| | - Zhenhui Chen
- From the Krannert Institute of Cardiology and the Departments of Medicine and
| | - Larry R Jones
- From the Krannert Institute of Cardiology and the Departments of Medicine and.
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19
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Colson BA, Gruber SJ, Thomas DD. Structural dynamics of muscle protein phosphorylation. J Muscle Res Cell Motil 2012; 33:419-29. [PMID: 22930331 DOI: 10.1007/s10974-012-9317-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 08/07/2012] [Indexed: 02/03/2023]
Abstract
We have used site-directed spectroscopic probes to detect structural changes, motions, and interactions due to phosphorylation of proteins involved in the regulation of muscle contraction and relaxation. Protein crystal structures provide static snapshots that provide clues to the conformations that are sampled dynamically by proteins in the cellular environment. Our site-directed spectroscopic experiments, combined with computational simulations, extend these studies into functional assemblies in solution, and reveal details of protein regions that are too dynamic or disordered for crystallographic approaches. Here, we discuss phosphorylation-mediated structural transitions in the smooth muscle myosin regulatory light chain, the striated muscle accessory protein myosin binding protein-C, and the cardiac membrane Ca(2+) pump modulator phospholamban. In each of these systems, phosphorylation near the N terminus of the regulatory protein relieves an inhibitory interaction between the phosphoprotein and its regulatory target. Several additional unifying themes emerge from our studies: (a) The effect of phosphorylation is not to change the affinity of the phosphoprotein for its regulated binding partner, but to change the structure of the bound complex without dissociation. (b) Phosphorylation induces transitions between order and dynamic disorder. (c) Structural states are only loosely coupled to phosphorylation; i.e., complete phosphorylation induces dramatic functional effects with only a partial shift in the equilibrium between ordered and disordered structural states. These studies, which offer atomic-resolution insight into the structural and functional dynamics of these phosphoproteins, were inspired in part by the ground-breaking work in this field by Michael and Kate Barany.
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Affiliation(s)
- Brett A Colson
- Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
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20
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Ceholski DK, Trieber CA, Young HS. Hydrophobic imbalance in the cytoplasmic domain of phospholamban is a determinant for lethal dilated cardiomyopathy. J Biol Chem 2012; 287:16521-9. [PMID: 22427649 DOI: 10.1074/jbc.m112.360859] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The sarco(endo)plasmic reticulum calcium ATPase (SERCA) and its regulatory partner phospholamban (PLN) are essential for myocardial contractility. Arg(9) → Cys (R9C) and Arg(14) deletion (R14del) mutations in PLN are associated with lethal dilated cardiomyopathy in humans. To better understand these mutations, we made a series of amino acid substitutions in the cytoplasmic domain of PLN and tested their ability to inhibit SERCA. R9C is a complete loss-of-function mutant of PLN, whereas R14del is a mild loss-of-function mutant. When combined with wild-type PLN to simulate heterozygous conditions, the mutants had a dominant negative effect on SERCA function. A series of targeted mutations in this region of the PLN cytoplasmic domain ((8)TRSAIRR(14)) demonstrated the importance of hydrophobic balance in proper PLN regulation of SERCA. We found that Arg(9) → Leu and Thr(8) → Cys substitutions mimicked the behavior of the R9C mutant, and an Arg(14) → Ala substitution mimicked the behavior of the R14del mutant. The results reveal that the change in hydrophobicity resulting from the R9C and R14del mutations is sufficient to explain the loss of function and persistent interaction with SERCA. Hydrophobic imbalance in the cytoplasmic domain of PLN appears to be a predictor for the development and progression of dilated cardiomyopathy.
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Affiliation(s)
- Delaine K Ceholski
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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