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Abstract
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To
characterize the conformational dynamics of sarcoplasmic reticulum
(SR) calcium pump (SERCA) we performed molecular dynamics simulations
beginning with several different high-resolution structures. We quantified
differences in structural disorder and dynamics for an open conformation
of SERCA versus closed structures and observed that dynamic motions
of SERCA cytoplasmic domains decreased with decreasing domain–domain
separation distance. The results are useful for interpretation of
recent intramolecular Förster resonance energy transfer (FRET)
distance measurements obtained for SERCA fused to fluorescent protein
tags. Those previous physical measurements revealed several discrete
structural substates and suggested open conformations of SERCA are
more dynamic than compact conformations. The present simulations support
this hypothesis and provide additional details of SERCA molecular
mechanisms. Specifically, all-atoms simulations revealed large-scale
translational and rotational motions of the SERCA N-domain relative
to the A- and P-domains during the transition from an open to a closed
headpiece conformation over the course of a 400 ns trajectory. The
open-to-closed structural transition was accompanied by a disorder-to-order
transition mediated by an initial interaction of an N-domain loop
(Nβ5-β6, residues 426–436) with residues 133–139
of the A-domain. Mutation of three negatively charged N-domain loop
residues abolished the disorder-to-order transition and prevented
the initial domain–domain interaction and subsequent closure
of the cytoplasmic headpiece. Coarse-grained molecular dynamics simulations
were in harmony with all-atoms simulations and physical measurements
and revealed a close communication between fluorescent protein tags
and the domain to which they were fused. The data indicate that previous
intramolecular FRET distance measurements report SERCA structure changes
with high fidelity and suggest a structural mechanism that facilitates
the closure of the SERCA cytoplasmic headpiece.
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Affiliation(s)
- Nikolai Smolin
- Department of Cell and Molecular Physiology, Stritch School of Medicine, Loyola University Chicago , Maywood, Illinois 60153, United States
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2
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Kekenes-Huskey PM, Metzger VT, Grant BJ, Andrew McCammon J. Calcium binding and allosteric signaling mechanisms for the sarcoplasmic reticulum Ca²+ ATPase. Protein Sci 2013; 21:1429-43. [PMID: 22821874 DOI: 10.1002/pro.2129] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The sarcoplasmic reticulum Ca²⁺ ATPase (SERCA) is a membrane-bound pump that utilizes ATP to drive calcium ions from the myocyte cytosol against the higher calcium concentration in the sarcoplasmic reticulum. Conformational transitions associated with Ca²⁺-binding are important to its catalytic function. We have identified collective motions that partition SERCA crystallographic structures into multiple catalytically-distinct states using principal component analysis. Using Brownian dynamics simulations, we demonstrate the important contribution of surface-exposed, polar residues in the diffusional encounter of Ca²⁺. Molecular dynamics simulations indicate the role of Glu309 gating in binding Ca²⁺, as well as subsequent changes in the dynamics of SERCA's cytosolic domains. Together these data provide structural and dynamical insights into a multistep process involving Ca²⁺ binding and catalytic transitions.
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Affiliation(s)
- Peter M Kekenes-Huskey
- Department of Pharmacology, University of California, San Diego, La Jolla, California 92093, USA.
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3
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Kekenes-Huskey PM, Gillette A, Hake J, McCammon JA. Finite Element Estimation of Protein-Ligand Association Rates with Post-Encounter Effects: Applications to Calcium binding in Troponin C and SERCA. ACTA ACUST UNITED AC 2012; 5. [PMID: 23293662 DOI: 10.1088/1749-4699/5/1/014015] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We introduce a computational pipeline and suite of software tools for the approximation of diffusion-limited binding based on a recently developed theoretical framework. Our approach handles molecular geometries generated from high-resolution structural data and can account for active sites buried within the protein or behind gating mechanisms. Using tools from the FEniCS library and the APBS solver, we implement a numerical code for our method and study two Ca(2+)-binding proteins: Troponin C and the Sarcoplasmic Reticulum Ca(2+) ATPase (SERCA). We find that a combination of diffusional encounter and internal 'buried channel' descriptions provide superior descriptions of association rates, improving estimates by orders of magnitude.
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Affiliation(s)
- P M Kekenes-Huskey
- Department of Pharmacology, University of California San Diego, La Jolla CA 92093
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4
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Musgaard M, Thøgersen L, Schiøtt B, Tajkhorshid E. Tracing cytoplasmic Ca(2+) ion and water access points in the Ca(2+)-ATPase. Biophys J 2012; 102:268-77. [PMID: 22339863 DOI: 10.1016/j.bpj.2011.12.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Revised: 11/17/2011] [Accepted: 12/05/2011] [Indexed: 11/28/2022] Open
Abstract
Sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) transports two Ca(2+) ions across the membrane of the sarco(endo)plasmic reticulum against the concentration gradient, harvesting the required energy by hydrolyzing one ATP molecule during each transport cycle. Although SERCA is one of the best structurally characterized membrane transporters, it is still largely unknown how the transported Ca(2+) ions reach their transmembrane binding sites in SERCA from the cytoplasmic side. Here, we performed extended all-atom molecular dynamics simulations of SERCA. The calculated electrostatic potential of the protein reveals a putative mechanism by which cations may be attracted to and bind to the Ca(2+)-free state of the transporter. Additional molecular dynamics simulations performed on a Ca(2+)-bound state of SERCA reveal a water-filled pathway that may be used by the Ca(2+) ions to reach their buried binding sites from the cytoplasm. Finally, several residues that are involved in attracting and guiding the cations toward the possible entry channel are identified. The results point to a single Ca(2+) entry site close to the kinked part of the first transmembrane helix, in a region loaded with negatively charged residues. From this point, a water pathway outlines a putative Ca(2+) translocation pathway toward the transmembrane ion-binding sites.
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Affiliation(s)
- Maria Musgaard
- Department of Chemistry, Aarhus University, Aarhus, Denmark
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Huang Y, Li H, Bu Y. Molecular dynamics simulation exploration of cooperative migration mechanism of calcium ions in sarcoplasmic reticulum Ca2+-ATPase. J Comput Chem 2009; 30:2136-45. [PMID: 19242958 DOI: 10.1002/jcc.21219] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Calcium ATPase is a member of the P-type ATPase, and it pumps calcium ions from the cytoplasm into the reticulum against a concentration gradient. Several X-ray structures of different conformations have been solved in recent years, providing basis for elucidating the active transport mechanism of Ca2+ ions. In this work, molecular dynamics (MD) simulations were performed at atomic level to investigate the dynamical process of calcium ions moving from the outer mouth of the protein to their binding sites. Five initial locations of Ca2+ ions were considered, and the simulations lasted for 2 or 6 ns, respectively. Specific pathways leading to the binding sites and large structural rearrangements around binding sites caused by uptake of calcium ions were identified. A cooperative binding mechanism was observed from our simulation. Firstly, the first Ca2+ ion binds to site I, and then, the second Ca2+ ion approaches. The interactions between the second Ca2+ and the residues around site I disturb the binding state of site I and weaken its binding ability for the first bound Ca2+. Because of the electrostatic repulsion of the second Ca2+ and the electrostatic attraction of site II, the first bound Ca2+ shifts from site I to site II. Concertedly, the second Ca2+ binds to site I, forming a binding state with two Ca2+ ions, one at site I and the other at site II. Both of Glu908 and Asp800 coordinate with the two Ca2+ ions simultaneously during the concerted binding process, which is believed to be the hinge to achieve the concerted binding. In our simulations, four amino acid residues that serve as the channel to link the outer mouth and the binding sites during the binding process were recognized, namely Tyr837, Tyr763, Asn911, and Ser767. The analyses regarding the activity of the proteins via mutations of some key residues also supported our cooperative mechanism.
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Affiliation(s)
- Yongqi Huang
- The Center for Modeling & Simulation Chemistry, Institute of Theoretical Chemistry, Shandong University, Jinan 250100, People's Republic of China
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6
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Karjalainen EL, Hauser K, Barth A. Proton paths in the sarcoplasmic reticulum Ca(2+) -ATPase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:1310-8. [PMID: 17904096 DOI: 10.1016/j.bbabio.2007.07.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2007] [Revised: 07/23/2007] [Accepted: 07/27/2007] [Indexed: 10/22/2022]
Abstract
The sarcoplasmic reticulum Ca(2+)-ATPase (SERCA1a) pumps Ca(2+) and countertransport protons. Proton pathways in the Ca(2+) bound and Ca(2+)-free states are suggested based on an analysis of crystal structures to which water molecules were added. The pathways are indicated by chains of water molecules that interact favorably with the protein. In the Ca(2+) bound state Ca(2)E1, one of the proposed Ca(2+) entry paths is suggested to operate additionally or alternatively as proton pathway. In analogs of the ADP-insensitive phosphoenzyme E2P and in the Ca(2+)-free state E2, the proton path leads between transmembrane helices M5 to M8 from the lumenal side of the protein to the Ca(2+) binding residues Glu-771, Asp-800 and Glu-908. The proton path is different from suggested Ca(2+) dissociation pathways. We suggest that separate proton and Ca(2+) pathways enable rapid (partial) neutralization of the empty cation binding sites. For this reason, transient protonation of empty cation binding sites and separate pathways for different ions are advantageous for P-type ATPases in general.
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Affiliation(s)
- Eeva-Liisa Karjalainen
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Svante Arrhenius väg 12, SE-106 91, Stockholm, Sweden
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Xiang F, Li P, Yan S, Sun L, Cukier RI, Bu Y. Hydration effect on interaction mode between glutamic acid and Ca2+ and its biochemical implication: a theoretical exploration. NEW J CHEM 2006. [DOI: 10.1039/b518408h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Fiorin G, Biekofsky RR, Pastore A, Carloni P. Unwinding the helical linker of calcium-loaded calmodulin: A molecular dynamics study. Proteins 2005; 61:829-39. [PMID: 16193483 DOI: 10.1002/prot.20597] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The fold of calmodulin (CaM) consists of two globular domains connected by a helical segment (the linker), whose conformational properties play a crucial role for the protein's molecular recognition processes. Here we investigate the structural properties of the linker by performing a 11.5 ns molecular dynamics (MD) simulation of calcium-loaded human CaM in aqueous solution. The calculations are based on the AMBER force field. The calculated S2 order parameters are in good accord with NMR data: The structure of the linker in our simulations is much more flexible than that emerging from the Homo sapiens X-ray structure, consistently with the helix unwinding observed experimentally in solution. This process occurs spontaneously in a nanosecond timescale, as observed also in a very recent simulation based on the GROMOS force field. A detailed description of the mechanism that determines the linker unwinding is provided, in which electrostatic contacts between the two globular domains play a critical role. The orientation of the domains emerging from our MD calculations is consistent both with former X-ray scattering data and a recent NMR work. Based on our findings, a rationale for the experimentally measured entropy cost associated to binding to the protein's cellular partners is also given.
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Affiliation(s)
- G Fiorin
- SISSA-International School for Advanced Studies, INFM-Democritos Modeling Center for Research in Atomistic Simulation, Trieste, Italy
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Vidossich P, Cascella M, Carloni P. Dynamics and energetics of water permeation through the aquaporin channel. Proteins 2004; 55:924-31. [PMID: 15146490 DOI: 10.1002/prot.10642] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Structural properties of water inside bovine aquaporin-1 are investigated by molecular simulation. The calculations, which are based on the recently determined X-ray structure at 2.2 A resolution (Sui et al., Nature 2001;414:872-878), are carried out on one monomeric subunit immersed in a water-n-octane-water bilayer. Molecular dynamics (MD) simulations suggest that His182, a fully conserved residue in the channel pore, is protonated in the delta position. Furthermore, they reveal a highly ordered water structure in the channel, induced by the electrostatic properties of the protein. Multiple-steering MD simulations are used to calculate the free-energy of water diffusion. To the best of our knowledge, this represents the first free-energy calculation based on the new, high-resolution structure of the pore. The calculated barrier is 2.5 kcal/mol, and it is associated to water permeation through the Asn-Pro-Ala (NPA) region of the pore, where water molecules are only hydrogen-bonded with themselves. These findings are fully consistent with those based on the previous MD studies on the human protein (de Groot and Grubmüller, Science 2001;294:2353-2357).
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Affiliation(s)
- Pietro Vidossich
- International School for Advanced Studies, S.I.S.S.A. and INFM-Democritos Modeling Center for Research In Atomistic Simulation, Trieste, Italy
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Abstract
The transport of Ca(2+) by Ca-ATPase across the sarcoplasmic reticulum membrane is accompanied by several transconformations of the protein. Relying on the already established functional importance of low-frequency modes in dynamics of proteins, we report here a normal mode analysis of the Ca(2+)-ATPase based on the crystallographic structures of the E1Ca(2) and E2TG forms. The lowest-frequency modes reveal that the N and A(+Nter) domains undergo the largest amplitude movements. The dynamical domain analysis performed with the DomainFinder program suggests that they behave as rigid bodies, unlike the highly flexible P domain. We highlight two types of movements of the transmembrane helices: i), a concerted movement around an axis perpendicular to the membrane which "twists open" the lumenal side of the protein and ii), an individual translational and rotational mobility which is of lower amplitude for the helices hosting the calcium binding sites. Among all modes calculated for E1Ca, only three are enough to describe the transition to E2TG; the associated movements involve almost exclusively the A and N domains, reflecting the closure of the cytoplasmic headpiece and high displacement of the L7-8 lumenal loop. Subsequently, we discuss the potential contribution of the remaining low-frequency normal modes to the transconformations occurring within the overall calcium transport cycle.
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Affiliation(s)
- Nathalie Reuter
- U410 INSERM. Faculté de médecine Xavier Bichat, Paris Cédex 18, France.
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Lenoir G, Picard M, Møller JV, le Maire M, Champeil P, Falson P. Involvement of the L6-7 loop in SERCA1a Ca2+-ATPase activation by Ca2+ (or Sr2+) and ATP. J Biol Chem 2004; 279:32125-33. [PMID: 15155750 DOI: 10.1074/jbc.m402934200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Wild-type (WT) and the double mutant D813A,D818A (ADA) of the L6-7 loop of SERCA1a were expressed in yeast, purified, and reconstituted into lipids. This allowed us to functionally study these ATPases by both kinetic and spectroscopic means, and to solve previous discrepancies in the published literature about both experimental facts and interpretation concerning the role of this loop in P-type ATPases. We show that in a solubilized state, the ADA mutant experiences a dramatic decrease of its calcium-dependent ATPase activity. On the contrary, reconstituted in a lipid environment, it displays an almost unaltered maximal calcium-dependent ATPase activity at high (millimolar) ATP, with an apparent affinity for Ca(2+) altered only moderately (3-fold). In the absence of ATP, the true affinity of ADA for Ca(2+) is, however, more significantly reduced (20-30-fold) compared with WT, as judged from intrinsic (Trp) or extrinsic (fluorescence isothiocyanate) fluorescence experiments. At low ATP, transient kinetics experiments reveal an overshoot in the ADA phosphorylation level primarily arising from the slowing down of the transition between the nonphosphorylated "E2" and "Ca(2)E1" forms of ADA. At high ATP, this slowing down is only partially compensated for, as ADA turnover remains more sensitive to orthovanadate than WT turnover. ADA ATPase also proved to have a reduced affinity for ATP in studies performed under equilibrium conditions in the absence of Ca(2+), highlighting the long range interactions between L6-7 and the nucleotide-binding site. We propose that these mutations in L6-7 could affect protonation-dependent winding and unwinding events in the nearby M6 transmembrane segment.
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Affiliation(s)
- Guillaume Lenoir
- Unité de Recherche Associée 2096, the Centre National de la Recherche Scientifique and Section de Biophysique des Fonctions Membranaires, Département de Biologie Joliot Curie, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
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Dal Peraro M, Vila AJ, Carloni P. Substrate binding to mononuclear metallo-β-lactamase from Bacillus cereus. Proteins 2003; 54:412-23. [PMID: 14747990 DOI: 10.1002/prot.10554] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Structure and dynamics of substrate binding (cefotaxime) to the catalytic pocket of the mononuclear zinc-beta-lactamase from Bacillus cereus are investigated by molecular dynamics simulations. The calculations, which are based on the hydrogen-bond pattern recently proposed by Dal Peraro et al. (J Biol Inorg Chem 2002; 7:704-712), are carried out for both the free and the complexed enzyme. In the resting state, active site pattern and temperature B-factors are in agreement with crystallographic data. In the complexed form, cefotaxime is accommodated into a stable orientation in the catalytic pocket within the nanosecond timescale, interacting with the enzyme zinc-bound hydroxide and the surrounding loops. The beta-lactam ring remains stable and very close to the hydroxide nucleophile agent, giving a stable representation of the productive enzyme-substrate complex.
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Affiliation(s)
- Matteo Dal Peraro
- International School for Advanced Studies, SISSA and INFM-DEMOCRITOS, Trieste, Italy
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