1
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Cao Y, Yang R, Wang W, Jiang S, Yang C, Wang Q, Liu N, Xue Y, Lee I, Meng X, Yuan Z. Effects of membrane lipids on phospholamban pentameric channel structure and ion transportation mechanisms. Int J Biol Macromol 2022; 224:766-775. [DOI: 10.1016/j.ijbiomac.2022.10.164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 10/10/2022] [Accepted: 10/19/2022] [Indexed: 11/05/2022]
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2
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Glaves JP, Primeau JO, Gorski PA, Espinoza-Fonseca LM, Lemieux MJ, Young HS. Interaction of a Sarcolipin Pentamer and Monomer with the Sarcoplasmic Reticulum Calcium Pump, SERCA. Biophys J 2019; 118:518-531. [PMID: 31858977 DOI: 10.1016/j.bpj.2019.11.3385] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Revised: 10/30/2019] [Accepted: 11/18/2019] [Indexed: 11/27/2022] Open
Abstract
The sequential rise and fall of cytosolic calcium underlies the contraction-relaxation cycle of muscle cells. Whereas contraction is initiated by the release of calcium from the sarcoplasmic reticulum, muscle relaxation involves the active transport of calcium back into the sarcoplasmic reticulum. This reuptake of calcium is catalyzed by the sarcoendoplasmic reticulum Ca2+-ATPase (SERCA), which plays a lead role in muscle contractility. The activity of SERCA is regulated by small membrane protein subunits, the most well-known being phospholamban (PLN) and sarcolipin (SLN). SLN physically interacts with SERCA and differentially regulates contractility in skeletal and atrial muscle. SLN has also been implicated in skeletal muscle thermogenesis. Despite these important roles, the structural mechanisms by which SLN modulates SERCA-dependent contractility and thermogenesis remain unclear. Here, we functionally characterized wild-type SLN and a pair of mutants, Asn4-Ala and Thr5-Ala, which yielded gain-of-function behavior comparable to what has been found for PLN. Next, we analyzed two-dimensional crystals of SERCA in the presence of wild-type SLN by electron cryomicroscopy. The fundamental units of the crystals are antiparallel dimer ribbons of SERCA, known for decades as an assembly of calcium-free SERCA molecules induced by the addition of decavanadate. A projection map of the SERCA-SLN complex was determined to a resolution of 8.5 Å, which allowed the direct visualization of an SLN pentamer. The SLN pentamer was found to interact with transmembrane segment M3 of SERCA, although the interaction appeared to be indirect and mediated by an additional density consistent with an SLN monomer. This SERCA-SLN complex correlated with the ability of SLN to decrease the maximal activity of SERCA, which is distinct from the ability of PLN to increase the maximal activity of SLN. Protein-protein docking and molecular dynamics simulations provided models for the SLN pentamer and the novel interaction between SERCA and an SLN monomer.
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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
| | - Przemek A Gorski
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - L Michel Espinoza-Fonseca
- Center for Arrhythmia Research, Department of Internal Medicine, Division of Cardiovascular 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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3
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Hartel AJW, Shekar S, Ong P, Schroeder I, Thiel G, Shepard KL. High bandwidth approaches in nanopore and ion channel recordings - A tutorial review. Anal Chim Acta 2019; 1061:13-27. [PMID: 30926031 PMCID: PMC6860018 DOI: 10.1016/j.aca.2019.01.034] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Accepted: 01/05/2019] [Indexed: 01/01/2023]
Abstract
Transport processes through ion-channel proteins, protein pores, or solid-state nanopores are traditionally recorded with commercial patch-clamp amplifiers. The bandwidth of these systems is typically limited to 10 kHz by signal-to-noise-ratio (SNR) considerations associated with these measurement platforms. At high bandwidth, the input-referred current noise in these systems dominates, determined by the input-referred voltage noise of the transimpedance amplifier applied across the capacitance at the input of the amplifier. This capacitance arises from several sources: the parasitic capacitance of the amplifier itself; the capacitance of the lipid bilayer harboring the ion channel protein (or the membrane used to form the solid-state nanopore); and the capacitance from the interconnections between the electronics and the membrane. Here, we review state-of-the-art applications of high-bandwidth conductance recordings of both ion channels and solid-state nanopores. These approaches involve tightly integrating measurement electronics fabricated in complementary metal-oxide semiconductors (CMOS) technology with lipid bilayer or solid-state membranes. SNR improvements associated with this tight integration push the limits of measurement bandwidths, in some cases in excess of 10 MHz. Recent case studies demonstrate the utility of these approaches for DNA sequencing and ion-channel recordings. In the latter case, studies with extended bandwidth have shown the potential for providing new insights into structure-function relations of these ion-channel proteins as the temporal resolutions of functional recordings matches time scales achievable with state-of-the-art molecular dynamics simulations.
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Affiliation(s)
- Andreas J W Hartel
- Bioelectronic Systems Laboratory, Department of Electrical Engineering, Columbia University, New York City, 10027, NY, USA.
| | - Siddharth Shekar
- Bioelectronic Systems Laboratory, Department of Electrical Engineering, Columbia University, New York City, 10027, NY, USA
| | - Peijie Ong
- Bioelectronic Systems Laboratory, Department of Electrical Engineering, Columbia University, New York City, 10027, NY, USA
| | - Indra Schroeder
- Plant Membrane Biophysics, Technische Universität Darmstadt, Darmstadt, Germany
| | - Gerhard Thiel
- Plant Membrane Biophysics, Technische Universität Darmstadt, Darmstadt, Germany
| | - Kenneth L Shepard
- Bioelectronic Systems Laboratory, Department of Electrical Engineering, Columbia University, New York City, 10027, NY, USA.
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4
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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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5
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Chipot C, Dehez F, Schnell JR, Zitzmann N, Pebay-Peyroula E, Catoire LJ, Miroux B, Kunji ERS, Veglia G, Cross TA, Schanda P. Perturbations of Native Membrane Protein Structure in Alkyl Phosphocholine Detergents: A Critical Assessment of NMR and Biophysical Studies. Chem Rev 2018; 118:3559-3607. [PMID: 29488756 PMCID: PMC5896743 DOI: 10.1021/acs.chemrev.7b00570] [Citation(s) in RCA: 117] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Indexed: 12/25/2022]
Abstract
Membrane proteins perform a host of vital cellular functions. Deciphering the molecular mechanisms whereby they fulfill these functions requires detailed biophysical and structural investigations. Detergents have proven pivotal to extract the protein from its native surroundings. Yet, they provide a milieu that departs significantly from that of the biological membrane, to the extent that the structure, the dynamics, and the interactions of membrane proteins in detergents may considerably vary, as compared to the native environment. Understanding the impact of detergents on membrane proteins is, therefore, crucial to assess the biological relevance of results obtained in detergents. Here, we review the strengths and weaknesses of alkyl phosphocholines (or foscholines), the most widely used detergent in solution-NMR studies of membrane proteins. While this class of detergents is often successful for membrane protein solubilization, a growing list of examples points to destabilizing and denaturing properties, in particular for α-helical membrane proteins. Our comprehensive analysis stresses the importance of stringent controls when working with this class of detergents and when analyzing the structure and dynamics of membrane proteins in alkyl phosphocholine detergents.
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Affiliation(s)
- Christophe Chipot
- SRSMC, UMR 7019 Université de Lorraine CNRS, Vandoeuvre-les-Nancy F-54500, France
- Laboratoire
International Associé CNRS and University of Illinois at Urbana−Champaign, Vandoeuvre-les-Nancy F-54506, France
- Department
of Physics, University of Illinois at Urbana−Champaign, 1110 West Green Street, Urbana, Illinois 61801, United States
| | - François Dehez
- SRSMC, UMR 7019 Université de Lorraine CNRS, Vandoeuvre-les-Nancy F-54500, France
- Laboratoire
International Associé CNRS and University of Illinois at Urbana−Champaign, Vandoeuvre-les-Nancy F-54506, France
| | - Jason R. Schnell
- Department
of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | - Nicole Zitzmann
- Department
of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | | | - Laurent J. Catoire
- Laboratory
of Biology and Physico-Chemistry of Membrane Proteins, Institut de Biologie Physico-Chimique (IBPC), UMR
7099 CNRS, Paris 75005, France
- University
Paris Diderot, Paris 75005, France
- PSL
Research University, Paris 75005, France
| | - Bruno Miroux
- Laboratory
of Biology and Physico-Chemistry of Membrane Proteins, Institut de Biologie Physico-Chimique (IBPC), UMR
7099 CNRS, Paris 75005, France
- University
Paris Diderot, Paris 75005, France
- PSL
Research University, Paris 75005, France
| | - Edmund R. S. Kunji
- Medical
Research Council Mitochondrial Biology Unit, University of Cambridge, Cambridge CB2 0XY, United Kingdom
| | - Gianluigi Veglia
- Department
of Biochemistry, Molecular Biology, and Biophysics, and Department
of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Timothy A. Cross
- National
High Magnetic Field Laboratory, Florida
State University, Tallahassee, Florida 32310, United States
| | - Paul Schanda
- Université
Grenoble Alpes, CEA, CNRS, IBS, Grenoble F-38000, France
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6
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Smeazzetto S, Tadini-Buoninsegni F, Thiel G, Moncelli MR. Selectivity of the phospholamban ion channel investigated by single channel measurements. J Electroanal Chem (Lausanne) 2018. [DOI: 10.1016/j.jelechem.2018.01.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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7
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Abstract
The calcium pump (a.k.a. Ca2+-ATPase or SERCA) is a membrane transport protein ubiquitously found in the endoplasmic reticulum (ER) of all eukaryotic cells. As a calcium transporter, SERCA maintains the low cytosolic calcium level that enables a vast array of signaling pathways and physiological processes (e.g. synaptic transmission, muscle contraction, fertilization). In muscle cells, SERCA promotes relaxation by pumping calcium ions from the cytosol into the lumen of the sarcoplasmic reticulum (SR), the main storage compartment for intracellular calcium. X-ray crystallographic studies have provided an extensive understanding of the intermediate states that SERCA populates as it progresses through the calcium transport cycle. Historically, SERCA is also known to be regulated by small transmembrane peptides, phospholamban (PLN) and sarcolipin (SLN). PLN is expressed in cardiac muscle, whereas SLN predominates in skeletal and atrial muscle. These two regulatory subunits play critical roles in cardiac contractility. While our understanding of these regulatory mechanisms are still developing, SERCA and PLN are one of the best understood examples of peptide-transporter regulatory interactions. Nonetheless, SERCA appeared to have only two regulatory subunits, while the related sodium pump (a.k.a. Na+, K+-ATPase) has at least nine small transmembrane peptides that provide tissue specific regulation. The last few years have seen a renaissance in our understanding of SERCA regulatory subunits. First, structures of the SERCA-SLN and SERCA-PLN complexes revealed molecular details of their interactions. Second, an array of micropeptides concealed within long non-coding RNAs have been identified as new SERCA regulators. This chapter will describe our current understanding of SERCA structure, function, and regulation.
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8
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Smeazzetto S, Armanious GP, Moncelli MR, Bak JJ, Lemieux MJ, Young HS, Tadini-Buoninsegni F. Conformational memory in the association of the transmembrane protein phospholamban with the sarcoplasmic reticulum calcium pump SERCA. J Biol Chem 2017; 292:21330-21339. [PMID: 29081402 DOI: 10.1074/jbc.m117.794453] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 10/19/2017] [Indexed: 11/06/2022] Open
Abstract
The sarcoplasmic reticulum Ca2+-ATPase SERCA promotes muscle relaxation by pumping calcium ions from the cytoplasm into the sarcoplasmic reticulum. SERCA activity is regulated by a variety of small transmembrane peptides, most notably by phospholamban in cardiac muscle and sarcolipin in skeletal muscle. However, how phospholamban and sarcolipin regulate SERCA is not fully understood. In the present study, we evaluated the effects of phospholamban and sarcolipin on calcium translocation and ATP hydrolysis by SERCA under conditions that mimic environments in sarcoplasmic reticulum membranes. For pre-steady-state current measurements, proteoliposomes containing SERCA and phospholamban or sarcolipin were adsorbed to a solid-supported membrane and activated by substrate concentration jumps. We observed that phospholamban altered ATP-dependent calcium translocation by SERCA within the first transport cycle, whereas sarcolipin did not. Using pre-steady-state charge (calcium) translocation and steady-state ATPase activity under substrate conditions (various calcium and/or ATP concentrations) promoting particular conformational states of SERCA, we found that the effect of phospholamban on SERCA depends on substrate preincubation conditions. Our results also indicated that phospholamban can establish an inhibitory interaction with multiple SERCA conformational states with distinct effects on SERCA's kinetic properties. Moreover, we noted multiple modes of interaction between SERCA and phospholamban and observed that once a particular mode of association is engaged it persists throughout the SERCA transport cycle and multiple turnover events. These observations are consistent with conformational memory in the interaction between SERCA and phospholamban, thus providing insights into the physiological role of phospholamban and its regulatory effect on SERCA transport activity.
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Affiliation(s)
- Serena Smeazzetto
- From the Department of Chemistry "Ugo Schiff," University of Florence, 50019 Sesto Fiorentino, Italy and
| | - Gareth P Armanious
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Maria Rosa Moncelli
- From the Department of Chemistry "Ugo Schiff," University of Florence, 50019 Sesto Fiorentino, Italy and
| | - Jessi J Bak
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - M Joanne Lemieux
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Howard S Young
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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9
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Espinoza-Fonseca LM. The Ca 2+-ATPase pump facilitates bidirectional proton transport across the sarco/endoplasmic reticulum. MOLECULAR BIOSYSTEMS 2017; 13:633-637. [PMID: 28290590 DOI: 10.1039/c7mb00065k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Ca2+ transport across the sarco/endoplasmic reticulum (SR) plays an essential role in intracellular Ca2+ homeostasis, signalling, cell differentiation and muscle contractility. During SR Ca2+ uptake and release, proton fluxes are required to balance the charge deficit generated by the exchange of Ca2+ and other ions across the SR. During Ca2+ uptake by the SR Ca2+-ATPase (SERCA), two protons are countertransported from the SR lumen to the cytosol, thus partially compensating for the charge moved by Ca2+ transport. Studies have shown that protons are also transported from the cytosol to the lumen during Ca2+ release, but a transporter that facilitates proton transport into the SR lumen has not been described. In this article we propose that SERCA forms pores that facilitate bidirectional proton transport across the SR. We describe the location and structure of water-filled pores in SERCA that form cytosolic and luminal pathways for protons to cross the SR membrane. Based on this structural information, we suggest mechanistic models for proton translocation to the cytosol during active Ca2+ transport, and into the SR lumen during SERCA inhibition by endogenous regulatory proteins. Finally, we discuss the physiological consequences of SERCA-mediated bidirectional proton transport across the SR membrane of muscle and non-muscle cells.
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Affiliation(s)
- L Michel Espinoza-Fonseca
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
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10
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Smeazzetto S, Tadini-Buoninsegni F, Thiel G, Berti D, Montis C. Phospholamban spontaneously reconstitutes into giant unilamellar vesicles where it generates a cation selective channel. Phys Chem Chem Phys 2015; 18:1629-36. [PMID: 26673394 DOI: 10.1039/c5cp05893g] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Phospholamban (PLN) is a small integral membrane protein, which modulates the activity of the Sarcoplasmic Reticulum Ca(2+)-ATPase (SERCA) of cardiac myocytes. PLN, as a monomer, can directly interact and tune SERCA activity, but the physiological function of the pentameric form is not yet fully understood and still debated. In this work, we reconstituted PLN in Giant Unilamellar Vesicles (GUVs), a simple and reliable experimental model system to monitor the activity of proteins in membranes. By Laser Scanning Confocal Microscopy (LSCM) and Fluorescence Correlation Spectroscopy (FCS) we verified a spontaneous reconstitution of PLN into the phospholipid bilayer. In parallel experiments, we measured with the patch clamp technique canonical ion channel fluctuations, which highlight a preference for Cs(+) over K(+) and do not conduct Ca(2+). The results prove that PLN forms, presumably in its pentameric form, a cation selective ion channel.
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Affiliation(s)
- S Smeazzetto
- Department of Chemistry "Ugo Schiff", University of Florence, Firenze, Italy
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11
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Smeazzetto S, Sacconi A, Schwan AL, Margheri G, Tadini-Buoninsegni F. Binding of a monoclonal antibody to the phospholamban cytoplasmic domain interferes with the channel activity of phospholamban reconstituted in a tethered bilayer lipid membrane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:10384-10388. [PMID: 25121716 DOI: 10.1021/la501660u] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Phospholamban (PLN), a membrane protein present in the sarcoplasmic reticulum of cardiac myocytes, is a crucial regulator of cardiac function. It is known that PLN appears as a monomer and as a pentamer. However, the role of the PLN pentamer and its ability to generate an ion channel are a matter of debate. To address this issue we employed an experimental approach that combines electrochemical impedance spectroscopy and surface plasmon resonance measurements. In particular, we investigated the channel activity of wild-type PLN reconstituted in a tethered bilayer lipid membrane (tBLM) on a gold surface. Our results indicate that reconstituted PLN can generate ion-conducting channels in a tBLM. Experiments with a PLN monoclonal antibody support an oriented incorporation of PLN in the tBLM. We show that the binding of the antibody to the PLN cytoplasmic domain interferes with PLN channel activity.
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Affiliation(s)
- Serena Smeazzetto
- Department of Chemistry "Ugo Schiff", University of Florence , 50019 Sesto Fiorentino, Italy
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12
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General rules for the arrangements and gating motions of pore-lining helices in homomeric ion channels. Nat Commun 2014; 5:4641. [PMID: 25105557 PMCID: PMC4133698 DOI: 10.1038/ncomms5641] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Accepted: 07/09/2014] [Indexed: 12/20/2022] Open
Abstract
The pore-lining helix (PLH) bundles are central to the function of all ion channels,
as their conformational rearrangements dictate channel gating. Here we explore all
plausible oligomeric arrangements of the PLH bundles within homomeric ion channels
by building models using generic restraints. In particular, the distance between two
neighbouring PLHs was bounded both below and above in order to avoid steric clash
and allow proper packing. The resulting models provide a theoretical representation
of the accessible space for oligomeric arrangements. While the represented space is
confined, it encompasses nearly all the ion channel PLH bundles for which the
structures are currently known. For a multitude of channels, gating models suggested
by paths within the confined accessible space are in qualitative agreement with
those established in previous structural and computational studies. Rearrangements of the pore-lining helix (PLH) bundles of ion channels
are central to their gating mechanisms. Here, Dai et al. use a modelling approach
to define the general rules that govern the arrangements and gating motions of the PLHs
in homomeric ion channels.
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13
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Becucci L, Foresti ML, Schwan A, Guidelli R. Can proton pumping by SERCA enhance the regulatory role of phospholamban and sarcolipin? BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2682-90. [DOI: 10.1016/j.bbamem.2013.07.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Revised: 06/22/2013] [Accepted: 07/08/2013] [Indexed: 11/26/2022]
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14
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Vostrikov VV, Mote KR, Verardi R, Veglia G. Structural dynamics and topology of phosphorylated phospholamban homopentamer reveal its role in the regulation of calcium transport. Structure 2013; 21:2119-30. [PMID: 24207128 DOI: 10.1016/j.str.2013.09.008] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 09/07/2013] [Accepted: 09/11/2013] [Indexed: 01/25/2023]
Abstract
Phospholamban (PLN) inhibits the sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA), thereby regulating cardiac diastole. In membranes, PLN assembles into homopentamers that in both the phosphorylated and nonphosphorylated states have been proposed to form ion-selective channels. Here, we determined the structure of the phosphorylated pentamer using a combination of solution and solid-state nuclear magnetic resonance methods. We found that the pinwheel architecture of the homopentamer is preserved upon phosphorylation, with each monomer having an L-shaped conformation. The TM domains form a hydrophobic pore approximately 24 Å long and 2 Å in diameter, which is inconsistent with canonical Ca²⁺-selective channels. Phosphorylation, however, enhances the conformational dynamics of the cytoplasmic region of PLN, causing partial unwinding of the amphipathic helix. We propose that PLN oligomers act as storage for active monomers, keeping SERCA function within a physiological window.
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Affiliation(s)
- Vitaly V Vostrikov
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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15
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Smeazzetto S, Saponaro A, Young HS, Moncelli MR, Thiel G. Structure-function relation of phospholamban: modulation of channel activity as a potential regulator of SERCA activity. PLoS One 2013; 8:e52744. [PMID: 23308118 PMCID: PMC3537670 DOI: 10.1371/journal.pone.0052744] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 11/20/2012] [Indexed: 11/22/2022] Open
Abstract
Phospholamban (PLN) is a small integral membrane protein, which binds and inhibits in a yet unknown fashion the Ca2+-ATPase (SERCA) in the sarcoplasmic reticulum. When reconstituted in planar lipid bilayers PLN exhibits ion channel activity with a low unitary conductance. From the effect of non-electrolyte polymers on this unitary conductance we estimate a narrow pore with a diameter of ca. 2.2 Å for this channel. This value is similar to that reported for the central pore in the structure of the PLN pentamer. Hence the PLN pentamer, which is in equilibrium with the monomer, is the most likely channel forming structure. Reconstituted PLN mutants, which either stabilize (K27A and R9C) or destabilize (I47A) the PLN pentamer and also phosphorylated PLN still generate the same unitary conductance of the wt/non-phosphorylated PLN. However the open probability of the phosphorylated PLN and of the R9C mutant is significantly lower than that of the respective wt/non-phosphorylated control. In the context of data on PLN/SERCA interaction and on Ca2+ accumulation in the sarcoplasmic reticulum the present results are consistent with the view that PLN channel activity could participate in the balancing of charge during Ca2+ uptake. A reduced total conductance of the K+ transporting PLN by phosphorylation or by the R9C mutation may stimulate Ca2+ uptake in the same way as an inhibition of K+ channels in the SR membrane. The R9C-PLN mutation, a putative cause of dilated cardiomyopathy, might hence affect SERCA activity also via its inherent low open probability.
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Affiliation(s)
| | - Andrea Saponaro
- Department of Biology and CNR IBF-Mi, Università degli Studi di Milano, Milano, Italy
| | - Howard S. Young
- Department of Biochemistry, University of Alberta, Edmonton, Canada
| | | | - Gerhard Thiel
- Plant Membrane Biophysics, TU-Darmstadt, Darmstadt, Germany
- * E-mail:
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