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Sharawi ZW, Khatrawi SM, Wang Q, Zhou H, Cyrus K, Yan G, Hoxter B, Haddad BR, Martin MB. Calcium Activation of the Androgen Receptor in Prostate Cells. Int J Endocrinol 2023; 2023:9907948. [PMID: 38131032 PMCID: PMC10733593 DOI: 10.1155/2023/9907948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 11/01/2023] [Accepted: 11/06/2023] [Indexed: 12/23/2023] Open
Abstract
Background Although prostate cancer patients initially respond to androgen deprivation therapy, most patients progress to a resistant phenotype. Castration resistance is due, in part, to intratumoral and/or adrenal synthesis of androgens, overexpression or mutation of the androgen receptor (AR), stabilization of AR by chaperones, and ligand-independent activation of AR. Increasing evidence also links disruption of calcium homeostasis to progression of prostate cancer. Our previous study shows that heavy metal cadmium activates the AR through a ligand-independent mechanism. Cadmium mimics calcium in biological systems due to their similar ionic charge and radius. This study determines whether calcium activates AR and whether first- and second-generation antiandrogens block the ability of calcium to activate the receptor. Methods The expression of androgen-responsive genes and calcium channels was measured in prostate cells using a quantitative real-time polymerase chain reaction assay. Cell growth was measured. Results To ask whether calcium activates AR, prostate cells were treated with calcium in the absence and presence of the first-generation antiandrogens hydroxyflutamide and bicalutamide and the second-generation antiandrogen enzalutamide, and the expression of androgen-responsive genes and cell growth was measured. In the normal PWR-1E cells and HEK293T cells transiently expressing AR, treatment with calcium increased the expression of androgen-responsive genes by approximately 3-fold. The increase was blocked by enzalutamide but was not consistently blocked by the first-generation antiandrogens. In LNCaP cells which contain a mutant AR, treatment with calcium also increased the expression of androgen-responsive genes by approximately 3-fold, and the increase was more effectively blocked by enzalutamide than by hydroxyflutamide or bicalutamide. Treatment with calcium also increased cell growth that was blocked by enzalutamide. To ask whether dysregulation of calcium channels is associated with castration resistance, calcium channels were measured in the normal PWR-1E prostate cells, the hormone-responsive LNCaP cells, and the castration-resistant VCaP and 22RV1 cells. Compared to normal prostate cells, the hormone-responsive and hormone-resistant cells overexpressed several calcium channels. Conclusions The results of this study show that calcium activates AR and increases cell growth and that calcium channels are overexpressed in hormone-responsive and hormone-resistant prostate cancer cells. Taken together, the results suggest a novel role of calcium in the castration-resistant phenotype.
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Affiliation(s)
- Zeina W. Sharawi
- Departments of Oncology, Georgetown University, Washington, DC 20007, USA
- Department of Genetics and Human Genetics, Howard University, Washington, DC 20059, USA
- Biological Sciences Department, Faculty of Sciences, King AbdulAziz University, Jeddah, Saudi Arabia
| | - Sawsan M. Khatrawi
- Departments of Biochemistry, Molecular and Cellular Biology, Georgetown University, Washington, DC 20007, USA
| | - Qiaochu Wang
- Departments of Biochemistry, Molecular and Cellular Biology, Georgetown University, Washington, DC 20007, USA
| | - Hongzhao Zhou
- Departments of Biochemistry, Molecular and Cellular Biology, Georgetown University, Washington, DC 20007, USA
| | - Kedra Cyrus
- Departments of Oncology, Georgetown University, Washington, DC 20007, USA
| | - Gai Yan
- Departments of Oncology, Georgetown University, Washington, DC 20007, USA
| | - Becky Hoxter
- Departments of Oncology, Georgetown University, Washington, DC 20007, USA
| | - Bassem R. Haddad
- Departments of Oncology, Georgetown University, Washington, DC 20007, USA
- Lombardi Comprehensive Cancer Center, Research Building, 3970 Reservoir Road NW, Washington, DC 20007, USA
| | - Mary Beth Martin
- Departments of Oncology, Georgetown University, Washington, DC 20007, USA
- Departments of Biochemistry, Molecular and Cellular Biology, Georgetown University, Washington, DC 20007, USA
- Lombardi Comprehensive Cancer Center, Research Building, 3970 Reservoir Road NW, Washington, DC 20007, USA
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Permyakov SE, Yundina EN, Kazakov AS, Permyakova ME, Uversky VN, Permyakov EA. Mouse S100G protein exhibits properties characteristic of a calcium sensor. Cell Calcium 2020; 87:102185. [PMID: 32114281 DOI: 10.1016/j.ceca.2020.102185] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 02/10/2020] [Accepted: 02/21/2020] [Indexed: 01/09/2023]
Abstract
Bovine S100 G (calbindin D9k, small Ca2+-binding protein of the EF-hand superfamily) is considered as a calcium buffer protein; i.e., the binding of Ca2+ practically does not change its general conformation. A set of experimental approaches has been used to study structural properties of apo- and Ca2+-loaded forms of mouse S100 G (81.4% identity in amino acid sequence with bovine S100 G). This analysis revealed that, in contrast to bovine S100 G, the removal of calcium ions increases α-helices content of mouse S100 G protein and enhances its accessibility to digestion by α-chymotrypsin. Furthermore, mouse apo-S100 G is characterized by a decreased surface hydrophobicity and reduced tendency for oligomerization. Such behavior is typical of calcium sensor proteins. Apo-state of mouse S100 G still has rather compact structure, which can be cooperatively unfolded by temperature and GdnHCl. Computational analysis of amino acid sequences of S100 G proteins shows that these proteins could be in a disordered state upon a removal of the bound calcium ions. The experimental data show that, although mouse apo-S100 G is flexible compared to the Ca2+-loaded state, the apo-form is not completely disordered and preserves some cooperatively meting structure. The origin of the unexpectedly high stability of mouse S100 G can be rationalized by an exceptionally strong association of its N- and C-terminal parts containing the EF-hands I and II, respectively.
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Affiliation(s)
- Sergei E Permyakov
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
| | - Elena N Yundina
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia
| | - Alexei S Kazakov
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia
| | - Maria E Permyakova
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia
| | - Vladimir N Uversky
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia; Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL, 33612, USA.
| | - Eugene A Permyakov
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia
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Thapa M, Johnson E, Rance M. Effect of monovalent ion binding on molecular dynamics of the S100-family calcium-binding protein calbindin D 9k. J Comput Chem 2019; 40:1936-1945. [PMID: 30977915 DOI: 10.1002/jcc.25839] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 02/25/2019] [Accepted: 03/23/2019] [Indexed: 11/06/2022]
Abstract
Calbindin D9k is a member of the S100 subfamily of EF-hand calcium binding proteins, and has served as an important model system for biophysical studies. The fast timescale dynamics of the calcium-free (apo) state is characterized using molecular dynamics simulations. Order parameters for the backbone NH bond vectors are determined from the simulations and compared with experimentally derived values, with a focus on the dynamics of calcium-binding site I. There is a significant discrepancy between simulated and experimental order parameters for site I residues in the case of no ion bound in site I. However, it was found in the simulations that a Na+ ion can bind in site I, and the resulting order parameters determined from the simulations are in excellent agreement with experiment. Comparisons are made to X-ray structures of other S100 family members in which Na+ ions were observed or suggested to be bound in site I. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
- Mahendra Thapa
- Department of Physics, University of Cincinnati, Cincinnati, Ohio
| | - Eric Johnson
- Department of Chemistry and Physical Sciences, Mount St. Joseph University, Cincinnati, Ohio
| | - Mark Rance
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio
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4
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Kukic P, Lundström P, Camilloni C, Evenäs J, Akke M, Vendruscolo M. Structural Insights into the Calcium-Mediated Allosteric Transition in the C-Terminal Domain of Calmodulin from Nuclear Magnetic Resonance Measurements. Biochemistry 2015; 55:19-28. [PMID: 26618792 DOI: 10.1021/acs.biochem.5b00961] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Calmodulin is a two-domain signaling protein that becomes activated upon binding cooperatively two pairs of calcium ions, leading to large-scale conformational changes that expose its binding site. Despite significant advances in understanding the structural biology of calmodulin functions, the mechanistic details of the conformational transition between closed and open states have remained unclear. To investigate this transition, we used a combination of molecular dynamics simulations and nuclear magnetic resonance (NMR) experiments on the Ca(2+)-saturated E140Q C-terminal domain variant. Using chemical shift restraints in replica-averaged metadynamics simulations, we obtained a high-resolution structural ensemble consisting of two conformational states and validated such an ensemble against three independent experimental data sets, namely, interproton nuclear Overhauser enhancements, (15)N order parameters, and chemical shift differences between the exchanging states. Through a detailed analysis of this structural ensemble and of the corresponding statistical weights, we characterized a calcium-mediated conformational transition whereby the coordination of Ca(2+) by just one oxygen of the bidentate ligand E140 triggers a concerted movement of the two EF-hands that exposes the target binding site. This analysis provides atomistic insights into a possible Ca(2+)-mediated activation mechanism of calmodulin that cannot be achieved from static structures alone or from ensemble NMR measurements of the transition between conformations.
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Affiliation(s)
- Predrag Kukic
- Department of Chemistry, University of Cambridge , Cambridge CB2 1EW, U.K
| | - Patrik Lundström
- Department of Physics, Chemistry and Biology, Linköping University , SE-581 83 Linköping, Sweden
| | - Carlo Camilloni
- Department of Chemistry, University of Cambridge , Cambridge CB2 1EW, U.K
| | - Johan Evenäs
- Red Glead Discovery , Medicon Village, SE-223 81 Lund, Sweden
| | - Mikael Akke
- Department of Biophysical Chemistry, Center for Molecular Protein Science, Lund University , SE-221 00 Lund, Sweden
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Amelia K, Singh J, Shah FH, Bhore SJ. Analysis of common bean (Phaseolus vulgaris L., genotype BAT93) calmodulin cDNA using computational tools. Pharmacognosy Res 2015; 7:209-12. [PMID: 25829797 PMCID: PMC4357974 DOI: 10.4103/0974-8490.150536] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2014] [Revised: 08/12/2014] [Accepted: 02/02/2015] [Indexed: 11/04/2022] Open
Abstract
BACKGROUND Common bean (Phaseolus vulgaris L.) is an important part of the human diet and serves as a source of natural products. Identification and understanding of genes in P. vulgaris is important for its improvement. Characterization of expressed sequence tags (ESTs) is one of the approaches in understanding the expressed genes. For the understanding of genes expression in P. vulgaris pod-tissue, research work of ESTs generation was initiated by constructing cDNA libraries using 5-day and 20-day old bean-pod-tissues. Altogether, 5972 cDNA clones were isolated to have ESTs. While processing ESTs, we found a transcript for calmodulin (CaM) gene. It is an important gene that encodes for a calcium-binding protein and known to express in all eukaryotic cells. Hence, this study was undertaken to analyse and annotate it. OBJECTIVE The objective of this study was to analyze and annotate P. vulgaris CaM (PvCaM) gene cDNA and its deduced protein (amino acids) sequence. MATERIALS AND METHODS Both strands of PvCaM cDNA clone were sequenced using M13 forward and reverse primer to elucidate the nucleotide sequence. The cDNA sequence and deduced protein sequence were analyzed and annotated using bioinformatics tools available online. The secondary structures and three-dimensional (3D) structure of PvCaM protein were predicted using the Phyre automatic fold recognition server. RESULTS Results showed that PvCaM cDNA is 818 bp in length. The cDNA analysis results showed that it contains an open reading frame that encodes for 149 amino acid residues. The deduced protein sequence analysis results showed the presence of conserved domains required for CaM function. The predicted secondary structures and 3D structure are analogous to the Solanum tuberosum CaM. CONCLUSIONS This study analyzed and annotated PvCaM cDNA and protein. However, in order to obtain a complete understanding of PvCaM protein, further study on its expression, structure and regulation is essential.
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Affiliation(s)
- Kassim Amelia
- Department of Molecular Biology, Melaka Institute of Biotechnology, Lot 7, Melaka International Trade Centre City, 75450 Ayer Keroh, Melaka ; Department of Biotechnology, Faculty of Applied Sciences, AIMST University, Semeling 08100, Kedah, Malaysia
| | - Jasvin Singh
- Department of Biotechnology, Faculty of Applied Sciences, AIMST University, Semeling 08100, Kedah, Malaysia
| | - Farida Habib Shah
- Department of Molecular Biology, Melaka Institute of Biotechnology, Lot 7, Melaka International Trade Centre City, 75450 Ayer Keroh, Melaka ; Department of Research and Development, Novel Plants Sdn. Bhd., 27C Jln Petaling Utama 12, 7.5 Miles Old Klang Road, 46000 Petaling Jaya, Malaysia
| | - Subhash J Bhore
- Department of Molecular Biology, Melaka Institute of Biotechnology, Lot 7, Melaka International Trade Centre City, 75450 Ayer Keroh, Melaka ; Department of Biotechnology, Faculty of Applied Sciences, AIMST University, Semeling 08100, Kedah, Malaysia
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Myoplasmic resting Ca2+ regulation by ryanodine receptors is under the control of a novel Ca2+-binding region of the receptor. Biochem J 2014; 460:261-71. [PMID: 24635445 PMCID: PMC4019983 DOI: 10.1042/bj20131553] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Passive SR (sarcoplasmic reticulum) Ca2+ leak through the RyR (ryanodine receptor) plays a critical role in the mechanisms that regulate [Ca2+]rest (intracellular resting myoplasmic free Ca2+ concentration) in muscle. This process appears to be isoform-specific as expression of either RyR1 or RyR3 confers on myotubes different [Ca2+]rest. Using chimaeric RyR3–RyR1 receptors expressed in dyspedic myotubes, we show that isoform-dependent regulation of [Ca2+]rest is primarily defined by a small region of the receptor encompassing amino acids 3770–4007 of RyR1 (amino acids 3620–3859 of RyR3) named as the CLR (Ca2+ leak regulatory) region. [Ca2+]rest regulation by the CLR region was associated with alteration of RyRs’ Ca2+-activation profile and changes in SR Ca2+-leak rates. Biochemical analysis using Tb3+-binding assays and intrinsic tryptophan fluorescence spectroscopy of purified CLR domains revealed that this determinant of RyRs holds a novel Ca2+-binding domain with conformational properties that are distinctive to each isoform. Our data suggest that the CLR region provides channels with unique functional properties that modulate the rate of passive SR Ca2+ leak and confer on RyR1 and RyR3 distinctive [Ca2+]rest regulatory properties. The identification of a new Ca2+-binding domain of RyRs with a key modulatory role in [Ca2+]rest regulation provides new insights into Ca2+-mediated regulation of RyRs. This paper reports the finding of a new class of Ca2+-binding domain of intracellular Ca2+ channels from muscle cells. This domain provides channels with distinctive properties that result in channel-specific modulation of the intracellular resting Ca2+ concentration.
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Edwards SJ, Moth CW, Kim S, Brandon S, Zhou Z, Cobb CE, Hustedt EJ, Beth AH, Smith JA, Lybrand TP. Automated structure refinement for a protein heterodimer complex using limited EPR spectroscopic data and a rigid-body docking algorithm: a three-dimensional model for an ankyrin-CDB3 complex. J Phys Chem B 2014; 118:4717-26. [PMID: 24758720 PMCID: PMC4018176 DOI: 10.1021/jp4099705] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
![]()
We report here specialized functions
incorporated recently in the
rigid-body docking software toolkit TagDock to utilize electron paramagnetic
resonance derived (EPR-derived) interresidue distance measurements
and spin-label accessibility data. The TagDock package extensions
include a custom methanethiosulfonate spin label rotamer library to
enable explicit, all-atom spin-label side-chain modeling and scripts
to evaluate spin-label surface accessibility. These software enhancements
enable us to better utilize the biophysical data routinely available
from various spin-labeling experiments. To illustrate the power and
utility of these tools, we report the refinement of an ankyrin:CDB3
complex model that exhibits much improved agreement with the EPR distance
measurements, compared to model structures published previously.
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Affiliation(s)
- Sarah J Edwards
- Department of Chemistry, ‡Department of Molecular Physiology & Biophysics, §Department of Biochemistry, ∥Department of Pharmacology, ⊥Center for Structural Biology, Vanderbilt University , Nashville, Tennessee 37235, United States
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Smith JA, Edwards SJ, Moth CW, Lybrand TP. TagDock: an efficient rigid body docking algorithm for oligomeric protein complex model construction and experiment planning. Biochemistry 2013; 52:5577-84. [PMID: 23875708 DOI: 10.1021/bi400158k] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report here new computational tools and strategies to efficiently generate three-dimensional models for oligomeric biomolecular complexes in cases where there is limited experimental restraint data to guide the docking calculations. Our computational tools are designed to rapidly and exhaustively enumerate all geometrically possible docking poses for an oligomeric complex, rather than generate detailed, atomic-resolution models. Experimental data, such as interatomic distance measurements, are then used to select and refine docking poses that are consistent with the experimental restraints. Our computational toolkit is designed for use with sparse data sets to generate intermediate-resolution docking models, and utilizes distance difference matrix analysis to identify further restraint measurements that will provide maximum additional structural refinement. Thus, these tools can be used to help plan optimal residue positions for probe incorporation in labor-intensive biophysical experiments such as chemical cross-linking, electron paramagnetic resonance, or Förster resonance energy transfer spectroscopy studies. We present benchmark results for docking the collection of all 176 heterodimer protein complexes from the ZDOCK database, as well as a protein homodimer with recently collected experimental distance restraints, to illustrate the toolkit's capabilities and performance, and to demonstrate how distance difference matrix analysis can automatically identify and prioritize additional restraint measurements that allow us to rapidly optimize docking poses.
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Affiliation(s)
- Jarrod A Smith
- Department of Biochemistry, Vanderbilt University, Box 351822, Nashville, TN 37235-1822, USA
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Byrne C, Divekar SD, Storchan GB, Parodi DA, Martin MB. Metals and breast cancer. J Mammary Gland Biol Neoplasia 2013; 18:63-73. [PMID: 23338949 PMCID: PMC4017651 DOI: 10.1007/s10911-013-9273-9] [Citation(s) in RCA: 128] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/26/2012] [Accepted: 01/10/2013] [Indexed: 12/18/2022] Open
Abstract
Metalloestrogens are metals that activate the estrogen receptor in the absence of estradiol. The metalloestrogens fall into two subclasses: metal/metalloid anions and bivalent cationic metals. The metal/metalloid anions include compounds such as arsenite, nitrite, selenite, and vanadate while the bivalent cations include metals such as cadmium, calcium, cobalt, copper, nickel, chromium, lead, mercury, and tin. The best studied metalloestrogen is cadmium. It is a heavy metal and a prevalent environmental contaminant with no known physiological function. This review addresses our current understanding of the mechanism by which cadmium and the bivalent cationic metals activate estrogen receptor-α. The review also summarizes the in vitro and in vivo evidence that cadmium functions as an estrogen and the potential role of cadmium in breast cancer.
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Affiliation(s)
- Celia Byrne
- Uniformed Services University of the Health Sciences, Bethesda, MD, USA
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Li AY, Lee J, Borek D, Otwinowski Z, Tibbits GF, Paetzel M. Crystal structure of cardiac troponin C regulatory domain in complex with cadmium and deoxycholic acid reveals novel conformation. J Mol Biol 2011; 413:699-711. [PMID: 21920370 PMCID: PMC4068330 DOI: 10.1016/j.jmb.2011.08.049] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Revised: 08/23/2011] [Accepted: 08/24/2011] [Indexed: 01/07/2023]
Abstract
The amino-terminal regulatory domain of cardiac troponin C (cNTnC) plays an important role as the calcium sensor for the troponin complex. Calcium binding to cNTnC results in conformational changes that trigger a cascade of events that lead to cardiac muscle contraction. The cardiac N-terminal domain of TnC consists of two EF-hand calcium binding motifs, one of which is dysfunctional in binding calcium. Nevertheless, the defunct EF-hand still maintains a role in cNTnC function. For its structural analysis by X-ray crystallography, human cNTnC with the wild-type primary sequence was crystallized under a novel crystallization condition. The crystal structure was solved by the single-wavelength anomalous dispersion method and refined to 2.2 Å resolution. The structure displays several novel features. Firstly, both EF-hand motifs coordinate cadmium ions derived from the crystallization milieu. Secondly, the ion coordination in the defunct EF-hand motif accompanies unusual changes in the protein conformation. Thirdly, deoxycholic acid, also derived from the crystallization milieu, is bound in the central hydrophobic cavity. This is reminiscent of the interactions observed for cardiac calcium sensitizer drugs that bind to the same core region and maintain the "open" conformational state of calcium-bound cNTnC. The cadmium ion coordination in the defunct EF-hand indicates that this vestigial calcium binding site retains the structural and functional elements that allow it to coordinate a cadmium ion. However, it is a result of, or concomitant with, large and unusual structural changes in cNTnC.
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Affiliation(s)
- Alison Yueh Li
- Department of Molecular Biology and Biochemistry, Simon Fraser University, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6
- Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6
| | - Jaeyong Lee
- Department of Molecular Biology and Biochemistry, Simon Fraser University, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6
| | - Dominika Borek
- Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Zbyszek Otwinowski
- Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Glen F. Tibbits
- Department of Molecular Biology and Biochemistry, Simon Fraser University, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6
- Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6
- Cardiovascular Sciences, Child and Family Research Institute, 950 West 28 Ave, Vancouver, BC, Canada V5Z 4H4
| | - Mark Paetzel
- Department of Molecular Biology and Biochemistry, Simon Fraser University, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6
- Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6
- Address correspondence to: Dr. Mark Paetzel, Simon Fraser University, Department of Molecular Biology and Biochemistry, South Science Building, 8888 University Drive, Burnaby, British Columbia, Canada V5A 1S6, Tel.: 778-782-4230, Fax.: 778-782-5583,
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Abstract
The EF hand, a helix-loop-helix structure, is one of the most common motifs found in animal genomes, and EF-hand Ca(2+)-binding proteins (EFCaBPs) are widely distributed throughout the cell. However, researchers remain confounded by a lack of understanding of how peptide sequences code for specific functions and by uncertainty about the molecular mechanisms that enable EFCaBPs to distinguish among many diverse cellular targets. Such knowledge could define the roles of EFCaBPs in health and disease and ultimately enable control or even design of Ca(2+)-dependent functions in medicine and biotechnology. In this Account, we describe our structural and biochemical research designed to understand the sequence-to-function relationship in EFCaBPs. The first structural goal was to define conformational changes induced by binding Ca(2+), and our group and others established that solution NMR spectroscopy is well suited for this task. We pinpointed residues critical to the differences in Ca(2+) response of calbindin D(9k) and calmodulin (CaM), homologous EFCaBPs from different functional classes, by using direct structure determination with site-directed mutagenesis and protein engineering. Structure combined with biochemistry provided the foundation for identifying the fundamental mechanism of cooperativity in the binding of Ca(2+) ions: this cooperativity provides EFCaBPs with the ability to detect the relatively small changes in concentration that constitute Ca(2+) signals. Using calbindin D(9k) as a model system, studies of the structure and fast time scale dynamics of each of the four ion binding states in a typical EF-hand domain provided direct evidence that site-site communication lowers the free energy cost of reorganization for binding the second ion. Our work has also extended models of how EFCaBPs interact with their cellular targets. We determined the unique dimeric architecture of S100 proteins, a specialized subfamily of EFCaBPs found exclusively in vertebrates. We described the implications for how these proteins transduce signals and went on to characterize interactions with peptide fragments of important cellular targets. Studies of the CaM homolog centrin revealed novel characteristics of its binding of Ca(2+) and its interaction with its cellular target Kar1. These results provided clear examples of how subtle differences in sequence fine-tune EFCaBPs to interact with their specific targets. The structural approach stands at a critical crossroad, shifting in emphasis from descriptive structural biochemistry to integrated biology and medicine. We present our dual-molecular-switch model for Ca(2+) regulation of gating functions of voltage-gated sodium channels in which both CaM and an intrinsic EF-hand domain serve as coupled Ca(2+) sensors. A second example involves novel EFCaBP extracellular function, that is, the role of S100A8/S100A9 heterodimer in the innate immune response to bacterial pathogens. A mechanism for the antimicrobial activity of S100A8/S100A9 was discovered. We describe interactions of S100A8/S100A9 and S100B with the cell surface receptor for advanced glycation end products. Biochemical and structural studies are now uncovering the mechanisms by which EFCaBPs work and are helping to define their biological activities, while simultaneously expanding knowledge of the roles of these proteins in normal cellular physiology and the pathology of disease.
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Affiliation(s)
- Walter J Chazin
- Department of Biochemistry and Chemistry, Vanderbilt University, Nashville, Tennessee 37232-8725, USA.
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Divekar SD, Storchan GB, Sperle K, Veselik DJ, Johnson E, Dakshanamurthy S, Lajiminmuhip YN, Nakles RE, Huang L, Martin MB. The role of calcium in the activation of estrogen receptor-alpha. Cancer Res 2011; 71:1658-68. [PMID: 21212417 DOI: 10.1158/0008-5472.can-10-1899] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Environmental estrogen mimics, including metalloestrogens that can activate estrogen receptor-alpha (ERα), may contribute to breast cancer risk. However, the underlying mechanisms through which these molecular mimics activate the ERα are generally poorly understood. With concern to this important question, we investigated whether intracellular calcium may mediate the cross-talk between signaling pathways that activate ERα and the ligand-binding domain of ERα. MCF-7 cells treated with EGF, ATP, extracellular calcium, or caffeine to increase intracellular calcium triggered a rapid recruitment of ERα to estrogen-responsive promoters and stimulated expression of estrogen-responsive genes including pS2, complement C3, and progesterone receptor. Induction was blocked by an antiestrogen but also by the chelation of intracellular calcium. Treatment with extracellular calcium also increased the growth of MCF-7 cells through an ER-dependent mechanism. We found that EGF and extracellular calcium activated the C-terminus of ERα and the activation was blocked by the antiestrogen. Mechanistic investigations identified four potential sites on the solvent-accessible surface of the ERα ligand-binding domain as important for calcium activation of the receptor. Taken together, our results suggest that calcium mediates the cross-talk between ERα-activating signaling pathways and the ligand-binding domain of ERα providing a potential explanation for the ability of certain environmental metalloestrogens to activate the receptor.
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Affiliation(s)
- Shailaja D Divekar
- Department of Biochemistry and Molecular & Cellular Biology, Georgetown University, Washington, District of Columbia, USA
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Lepsík M, Field MJ. Binding of calcium and other metal ions to the EF-hand loops of calmodulin studied by quantum chemical calculations and molecular dynamics simulations. J Phys Chem B 2007; 111:10012-22. [PMID: 17661504 DOI: 10.1021/jp0716583] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Calcium ion binding by the four EF-hand motifs of the protein calmodulin (CaM) is a central event in Ca2+-based cellular signaling. To understand molecular details of this complex process, isolated Ca2+-binding loops can be studied, by use of both experiments and calculations. In this work, we explore the metal specificity of the four Ca2+-binding loops of CaM using density functional theory (DFT) quantum chemical calculations and molecular dynamics simulations. We study CaM complexes with the physiologically important ions of calcium (Ca2+) and magnesium (Mg2+) and also with two other ions, strontium (Sr2+) and lanthanum (La3+). The former is of interest in the area of radioactive waste bioremediation, whereas the latter is often used as a probe of Ca2+-binding sites. We obtain intrinsic metal ion-loop binding energies as well as their components: vacuum, charge-transfer, solvation, entropy, and deformation terms. A detailed analysis of the results reveals that the total binding energy depends on a delicate balance among these energy components. They, in turn, are determined by the cation's charge and size as well as the amino acid composition and flexibility of the loops and the identity of the metal-chelating residues.
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Affiliation(s)
- Martin Lepsík
- Laboratoire de Dynamique Moléculaire, Institut de Biologie Structurale-Jean-Pierre Ebel, 41 rue Jules Horowitz, 38027 Grenoble Cedex 1, France.
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14
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Garner J, Deadman J, Rhodes D, Griffith R, Keller PA. A new methodology for the simulation of flexible protein–ligand interactions. J Mol Graph Model 2007; 26:187-97. [PMID: 17229583 DOI: 10.1016/j.jmgm.2006.11.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2006] [Revised: 10/16/2006] [Accepted: 11/15/2006] [Indexed: 10/23/2022]
Abstract
A methodology has been developed for the simulation of induced fit between a ligand and its target protein. It utilizes constrained molecular dynamics where atoms determined to be immobile from difference distance matrix studies are fixed. Application of this methodology to HIV-1 reverse transcriptase (RT) as the example target protein has demonstrated its robustness. Short simulation times are sufficient to achieve good refinement of docking poses resulting from exchange of structurally dissimilar inhibitors between crystal structures.
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Affiliation(s)
- James Garner
- Department of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia
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15
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Gifford JL, Walsh MP, Vogel HJ. Structures and metal-ion-binding properties of the Ca2+-binding helix–loop–helix EF-hand motifs. Biochem J 2007; 405:199-221. [PMID: 17590154 DOI: 10.1042/bj20070255] [Citation(s) in RCA: 630] [Impact Index Per Article: 37.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The ‘EF-hand’ Ca2+-binding motif plays an essential role in eukaryotic cellular signalling, and the proteins containing this motif constitute a large and functionally diverse family. The EF-hand is defined by its helix–loop–helix secondary structure as well as the ligands presented by the loop to bind the Ca2+ ion. The identity of these ligands is semi-conserved in the most common (the ‘canonical’) EF-hand; however, several non-canonical EF-hands exist that bind Ca2+ by a different co-ordination mechanism. EF-hands tend to occur in pairs, which form a discrete domain so that most family members have two, four or six EF-hands. This pairing also enables communication, and many EF-hands display positive co-operativity, thereby minimizing the Ca2+ signal required to reach protein saturation. The conformational effects of Ca2+ binding are varied, function-dependent and, in some cases, minimal, but can lead to the creation of a protein target interaction site or structure formation from a molten-globule apo state. EF-hand proteins exhibit various sensitivities to Ca2+, reflecting the intrinsic binding ability of the EF-hand as well as the degree of co-operativity in Ca2+ binding to paired EF-hands. Two additional factors can influence the ability of an EF-hand to bind Ca2+: selectivity over Mg2+ (a cation with very similar chemical properties to Ca2+ and with a cytoplasmic concentration several orders of magnitude higher) and interaction with a protein target. A structural approach is used in this review to examine the diversity of family members, and a biophysical perspective provides insight into the ability of the EF-hand motif to bind Ca2+ with a wide range of affinities.
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Affiliation(s)
- Jessica L Gifford
- Structural Biology Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
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16
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Huang Y, Zhou Y, Yang W, Butters R, Lee HW, Li S, Castiblanco A, Brown EM, Yang JJ. Identification and dissection of Ca(2+)-binding sites in the extracellular domain of Ca(2+)-sensing receptor. J Biol Chem 2007; 282:19000-10. [PMID: 17478419 PMCID: PMC2867057 DOI: 10.1074/jbc.m701096200] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Ca(2+)-sensing receptors (CaSRs) represent a class of receptors that respond to changes in the extracellular Ca(2+) concentration ([Ca(2+)](o)) and activate multiple signaling pathways. A major barrier to advancing our understanding of the role of Ca(2+) in regulating CaSRs is the lack of adequate information about their Ca(2+)-binding locations, which is largely hindered by the lack of a solved three-dimensional structure and rapid off rates due to low Ca(2+)-binding affinities. In this paper, we have reported the identification of three potential Ca(2+)-binding sites in a modeled CaSR structure using computational algorithms based on the geometric description and surface electrostatic potentials. Mutation of the predicted ligand residues in the full-length CaSR caused abnormal responses to [Ca(2+)](o), similar to those observed with naturally occurring activating or inactivating mutations of the CaR, supporting the essential role of these predicted Ca(2+)-binding sites in the sensing capability of the CaSR. In addition, to probe the intrinsic Ca(2+)-binding properties of the predicted sequences, we engineered two predicted continuous Ca(2+)-binding sequences individually into a scaffold protein provided by a non-Ca(2+)-binding protein, CD2. We report herein the estimation of the metal-binding affinities of these predicted sites in the CaSR by monitoring aromatic-sensitized Tb(3+) fluorescence energy transfer. Removing the predicted Ca(2+)-binding ligands resulted in the loss of or significantly weakened cation binding. The potential Ca(2+)-binding residues were shown to be involved in Ca(2+)/Ln(3+) binding by high resolution NMR and site-directed mutagenesis, further validating our prediction of Ca(2+)-binding sites within the extracellular domain of the CaSR.
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MESH Headings
- Algorithms
- Animals
- Binding Sites/physiology
- Calcium/metabolism
- Cell Line
- Extracellular Space/metabolism
- Humans
- Kidney/cytology
- Mice
- Models, Chemical
- Mutagenesis, Site-Directed
- Nuclear Magnetic Resonance, Biomolecular
- Protein Engineering
- Protein Structure, Quaternary
- Protein Structure, Tertiary
- Receptors, Calcium-Sensing/chemistry
- Receptors, Calcium-Sensing/genetics
- Receptors, Calcium-Sensing/metabolism
- Receptors, Metabotropic Glutamate/chemistry
- Receptors, Metabotropic Glutamate/metabolism
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Affiliation(s)
- Yun Huang
- Department of Chemistry, Center for Biotechnology and Drug Design Georgia State University, Atlanta, Georgia 30303
| | - Yubin Zhou
- Department of Chemistry, Center for Biotechnology and Drug Design Georgia State University, Atlanta, Georgia 30303
| | - Wei Yang
- Department of Chemistry, Center for Biotechnology and Drug Design Georgia State University, Atlanta, Georgia 30303
| | - Robert Butters
- Division of Endocrinology, Diabetes and Hypertension, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - Hsiau-Wei Lee
- Department of Chemistry, Center for Biotechnology and Drug Design Georgia State University, Atlanta, Georgia 30303
| | - Shunyi Li
- Department of Chemistry, Center for Biotechnology and Drug Design Georgia State University, Atlanta, Georgia 30303
| | - Adriana Castiblanco
- Department of Chemistry, Center for Biotechnology and Drug Design Georgia State University, Atlanta, Georgia 30303
| | - Edward M. Brown
- Division of Endocrinology, Diabetes and Hypertension, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 02115
| | - Jenny J. Yang
- Department of Chemistry, Center for Biotechnology and Drug Design Georgia State University, Atlanta, Georgia 30303
- To whom correspondence should be addressed: Dept. of Chemistry, Georgia State University, University Plaza, Atlanta, GA 30303. Tel.: 404-651-4620; Fax: 404-651-2751;
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17
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Fragai M, Luchinat C, Parigi G. "Four-dimensional" protein structures: examples from metalloproteins. Acc Chem Res 2006; 39:909-17. [PMID: 17176029 DOI: 10.1021/ar050103s] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The fact that an object, for example, a protein, possesses a three-dimensional structure seems an obvious concept. However, when the object is flexible, the concept is less obvious. Growing experimental data over several decades show that proteins are not rigid objects, but they may sample more or less wide ranges of different conformations. To stress this concept, we propose to call the range of sampled conformations the "fourth dimension" of the protein structure. Nuclear magnetic resonance is a precious technique to define this fourth dimension. Examples of conformational heterogeneity taken from the realm of metalloproteins and their functional implications are discussed.
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Affiliation(s)
- Marco Fragai
- Centro Risonanze Magnetiche (CERM) and Department of Agricultural Biotechnology, University of Florence, Via Luigi Sacconi, 6, 50019 Sesto Fiorentino (Florence), Italy
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18
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Balayssac S, Jiménez B, Piccioli M. Assignment strategy for fast relaxing signals: complete aminoacid identification in thulium substituted calbindin D 9K. JOURNAL OF BIOMOLECULAR NMR 2006; 34:63-73. [PMID: 16518694 DOI: 10.1007/s10858-005-5359-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2005] [Accepted: 11/14/2005] [Indexed: 05/07/2023]
Abstract
Paramagnetic proteins generally contain regions with diverse relaxation properties. Nuclei in regions far from the metal center may behave like those in diamagnetic proteins, but those closer to the metal experience rapid relaxation with accompanying line broadening. We have used a set of NMR experiments optimized to capture data from these various concentric regions in assigning the signals from a paramagnetic Calbindin D 9K derivative in which one of the two calcium ions has been replaced by thulium(III). Normal double- and triple-resonance experiments with 1H detection were used in collecting data from nuclei in the diamagnetic-like region; these approaches identified signals from fewer than 50% of the amino acid residues (those with d > 17.5 A from thulium(III)). Paramagnetism-optimized two-dimensional NMR experiments with 1H detection were used in collecting data from nuclei in the next nearer region (d > 15 A). Standard (d > 14 A) and optimized (d > 9 A) 13C direct-detection experiments were used to capture data from nuclei in the next layer. Finally nuclei closest to the metal were detected by one-dimensional 13C (d > 5 A) and one-dimensional 15N data collection (d > 4.2 A). NMR signals were assigned on the basis of through-bond correlations and, for signals closest to the metal, pseudocontact shifts. The latter were determined from chemical shift differences between assigned signals in thulium(III) and lanthanum(III) derivatives of Calbindin D 9K and they were interpreted on the basis of a structural model for the lanthanide-substituted protein. This approach yielded assignments of at least one resonance per amino acid residue, including those in the thulium(III) coordination sphere.
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Affiliation(s)
- Stéphane Balayssac
- Department of Chemistry, Magnetic Resonance Center (CERM), University of Florence, Via Luigi Sacconi 6, 50019, Sesto Fiorentino, Florence, Italy
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19
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Babini E, Bertini I, Capozzi F, Luchinat C, Quattrone A, Turano M. Principal Component Analysis of the Conformational Freedom within the EF-Hand Superfamily. J Proteome Res 2005; 4:1961-71. [PMID: 16335940 DOI: 10.1021/pr050148n] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A database of nonredundant structures of EF-hand domains--i.e., pairs of helix-loop-helix motifs--has been assembled, and the six angles among the four helices re-determined. A principal component analysis of these angles allows us to use two such components (PC1 and PC2) to describe the system retaining 80% of the total variance. A PC2 against PC1 plot representation allows us to represent in a compact way the full range of structural diversity of EF-hand domains, their grouping into protein families, and the variation for each family upon calcium and peptide binding.
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Affiliation(s)
- Elena Babini
- Department of Food Science, University of Bologna, 47023 Cesena, Italy
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20
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Malmendal A, Vander Kooi CW, Nielsen NC, Chazin WJ. Calcium-modulated S100 protein-phospholipid interactions. An NMR study of calbindin D9k and DPC. Biochemistry 2005; 44:6502-12. [PMID: 15850384 DOI: 10.1021/bi050088z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The cellular functions of several S100 proteins involve specific interactions with phospholipids and the cell membrane. The interactions between calbindin D(9k) (S100D) and the detergent dodecyl phosphocholine (DPC) were studied using NMR spectroscopy. In the absence of Ca(2+), the protein associates with DPC micelles. The micelle-associated state has intact helical secondary structures but no apparent tertiary fold. At neutral pH, Ca(2+)-loaded calbindin D(9k) does not associate with DPC micelles. However, a specific interaction is observed with individual DPC molecules at a site close to the linker between the two EF-hands. Binding to this site occurs only when Ca(2+) is bound to the protein. A reduction in pH in the absence of Ca(2+) increases the stability of the micelle-associated state. This along with the corresponding reduction in Ca(2+) affinity causes a transition to the micelle-associated state also in the presence of Ca(2+) when the pH is lowered. Site-specific analysis of the data indicates that calbindin D(9k) has a core of three tightly packed helices (A, B, and D), with a dynamic fourth helix (C) more loosely associated. Evidence is presented that the Ca(2+)-binding characteristics of the two EF-hands are distinctly different in a micelle environment. The role of calbindin D(9k) in the cell is discussed, along with the broader implications for the function of the S100 protein family.
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Affiliation(s)
- Anders Malmendal
- Department of Biochemistry, Center for Structural Biology, 5140 BIOSCI/MRB III, Vanderbilt University, Nashville, Tennessee 37232-8725, USA.
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21
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Ye Y, Lee HW, Yang W, Shealy S, Yang JJ. Probing Site-Specific Calmodulin Calcium and Lanthanide Affinity by Grafting. J Am Chem Soc 2005; 127:3743-50. [PMID: 15771508 DOI: 10.1021/ja042786x] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ca2+ binding is essential for the biological functions of calmodulin (CaM) as a trigger/sensor protein to regulate many biological processes in the Ca2+ -signaling cascade. A challenge in understanding the mechanism of Ca2+ signaling is to obtain site-specific information about the Ca2+ binding properties of individual Ca2+ -binding sites of EF-hand proteins, especially for CaM. In this paper, we report the first estimation of the intrinsic Ca2+ affinities of the four EF-hand loops of calmoduin (I-IV) by individually grafting into the domain 1 of CD2. Taking advantage of the Trp residues in the host protein, we first determined metal-binding affinities for Tb3+, Ca2+, and La3+ for all four grafted EF-loops using Tb3+ aromatic resonance energy transfer. EF-loop I exhibits the strongest binding affinity for Ca2+, La3+, and Tb3+, while EF-loop IV has the weakest metal-binding affinity. EF-loops I-IV of CaM have dissociation constants for Ca2+ of 34, 245, 185, and 814 microM, respectively, with the order I > III approximately equal to II > IV. These findings support a charge-ligand-balanced model in which both the number of negatively charged ligand residues and the balanced electrostatic dentate-dentate repulsion by the adjacent charged residues are two major determinants for the relative Ca2+ -binding affinities of EF-loops in CaM. Our grafting method provides a new strategy to obtain site-specific Ca2+ binding properties and a better estimation of the cooperativity and conformational change contributions of coupled EF-hand proteins.
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Affiliation(s)
- Yiming Ye
- Department of Chemistry, Center for Drug Design and Advanced Biotechnology, Georgia State University, Atlanta, Georgia 30303, USA
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22
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Finley NL, Howarth JW, Rosevear PR. Structure of the Mg2+-loaded C-lobe of cardiac troponin C bound to the N-domain of cardiac troponin I: comparison with the Ca2+-loaded structure. Biochemistry 2004; 43:11371-9. [PMID: 15350124 DOI: 10.1021/bi049672i] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cardiac troponin C (cTnC) is the Ca(2+)-binding component of the troponin complex and, as such, is the Ca(2+)-dependent switch in muscle contraction. This protein consists of two globular lobes, each containing a pair of EF-hand metal-binding sites, connected by a linker. In the N lobe, Ca(2+)-binding site I is inactive and Ca(2+)-binding site II is primarily responsible for initiation of muscle contraction. The C lobe contains Ca(2+)/Mg(2+)-binding sites III and IV, which bind Mg(2+) with lower affinity and play a structural as well as a secondary role in modulating the Ca(2+) signal. To understand the structural consequences of Ca(2+)/Mg(2+) exchange in the C lobe, we have determined the NMR solution structure of the Mg(2+)-loaded C lobe, cTnC(81-161), in a complex with the N domain of cardiac troponin I, cTnI(33-80), and compared it with a refined Ca(2+)-loaded structure. The overall tertiary structure of the Mg(2+)-loaded C lobe is very similar to that of the refined Ca(2+)-loaded structure as evidenced by the root-mean-square deviation of 0.94 A for all backbone atoms. While metal-dependent conformational changes are minimal, substitution of Mg(2+) for Ca(2+) is characterized by condensation of the C-terminal portion of the metal-binding loops with monodentate Mg(2+) ligation by the conserved Glu at position 12 and partial closure of the cTnI hydrophobic binding cleft around site IV. Thus, conformational plasticity in the Ca(2+)/Mg(2+)-dependent binding loops may represent a mechanism to modulate C-lobe cTnC interactions with the N domain of cTnI.
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Affiliation(s)
- Natosha L Finley
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Medical Sciences Building, Cincinnati Ohio 45267-0524, USA
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23
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Liu Y, Liu Z, Androphy E, Chen J, Baleja JD. Design and characterization of helical peptides that inhibit the E6 protein of papillomavirus. Biochemistry 2004; 43:7421-31. [PMID: 15182185 DOI: 10.1021/bi049552a] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The E6 protein from HPV type 16 binds proteins containing a seven-residue leucine-containing motif. Previous work demonstrated that peptides containing the consensus sequence are a mixture of alpha-helix and unstructured conformations. To design monomeric E6-binding peptides that are stable in aqueous solution, we used a protein grafting approach where the critical residues of the E6-binding motif of E6-associated protein, E6AP, LQELLGE, were incorporated into exposed helices of two stably folded peptide scaffolds. One series was built using the third zinc finger of the Sp1 protein, which contains a C-terminal helix. A second series was built using a Trp-cage scaffold, which contains an N-terminal helix. The chimeric peptides had very different activities in out-competing the E6-E6AP interaction. We characterized the peptides by circular dichroism spectroscopy and determined high-resolution structures by NMR methods. The E6-binding consensus motif was found to be helical in the high-quality structures, which had backbone root-mean-square deviations of less than 0.4 A. We have successfully grafted the E6-binding motif into two parent peptides to create ligands that have biological activity while preserving the stable, native fold of their scaffolds. The data also indicate that conformational change is common in E6-binding proteins during the formation of the complex with the viral E6 protein.
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Affiliation(s)
- Yuqi Liu
- Department of Biochemistry, Tufts University School of Medicine, 136 Harrison Avenue, Boston, Massachusetts 02111, USA
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24
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Rabiller-Baudry M, Chaufer B. Small molecular ion adsorption on proteins and DNAs revealed by separation techniques. J Chromatogr B Analyt Technol Biomed Life Sci 2004; 797:331-45. [PMID: 14630159 DOI: 10.1016/s1570-0232(03)00488-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Ion binding is a term that assumes that the ion is included in the solvation sphere characterising the biomolecule. The binding forces are not clearly stated except for electrostatic attraction; weak forces (hydrogen bonds and Van der Waals forces) are likely involved. Many publications have dealt with ion binding to proteins and the consequences over the past 10 years, but only a few studies were performed using high-performance liquid chromatography (HPLC: ion exchange, reversed phase without the well-identified immobilised metal affinity chromatography) and capillary zone electrophoresis (CZE). This review focuses on the binding of proteins and DNAs mainly to the oxyanions (phosphate, borate, citrate) and amines used as buffers for both the HPLC eluent and the background electrolyte of CZE. Such specific ion adsorption on biomolecules is evidenced by physico-chemical characteristics such as the mobility or retention volume, closely associated with the net charge, which differ from the expected or experimental data obtained under the conditions of an indifferent electrolyte. It is shown that ion binding to proteins is a key parameter in the electrostatic repulsion between the free protein and a fouled membrane in the ultrafiltration separation of a protein mixture.
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Affiliation(s)
- Murielle Rabiller-Baudry
- Laboratoire des Procédés de Séparation, Université Rennes 1, UC INRA, Campus de Beaulieu, Bat. 10A, 263 Avenue du Général Leclerc, CS 74205, 35042 Rennes Cedex, France.
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25
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Cao ZW, Chen X, Chen YZ. Correlation between normal modes in the 20-200 cm-1 frequency range and localized torsion motions related to certain collective motions in proteins. J Mol Graph Model 2003; 21:309-19. [PMID: 12479929 DOI: 10.1016/s1093-3263(02)00185-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In certain biologically relevant collective motions, such as protein domain motions and sub-domain motions, large amplitude movements are localized in one or a few flexible regions consisting of a small number of residues. This paper explores the possible use of normal mode analysis in probing localized vibrational torsion motions in these flexible regions that may be related to certain collective motions. The normal modes of 10 structures of five proteins in different conformation (TRP repressor, calmodulin, calbindin D(9k), HIV-1 protease and troponin C), known to have shear or hinge domain or sub-domain motion, respectively, are analyzed. Our study identifies, for each structure, unique normal modes in the 20-200 cm-1 frequency range, whose corresponding motions are primarily concentrated in the region where large amplitude torsion movements of a known domain or sub-domain motion occur. This suggests possible correlation between normal modes at 20-200 cm-1 frequency range and initial fluctuational motions leading to localized collective motions in proteins, and thus the potential application of normal mode analysis in facilitating the study of biologically important localized motions in biomolecules.
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Affiliation(s)
- Z W Cao
- Department of Computational Science, National University of Singapore, 3 Science Drive 2, Singapore 117543, Singapore
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26
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Ferrari R, Bernés S, de Barbarı́n CR, Mendoza-Dı́az G, Gasque L. Interaction between Glyglu and Ca2+, Pb2+, Cd2+ and Zn2+ in solid state and aqueous solution. Inorganica Chim Acta 2002. [DOI: 10.1016/s0020-1693(02)01047-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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27
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Georgescu RE, Alexov EG, Gunner MR. Combining conformational flexibility and continuum electrostatics for calculating pK(a)s in proteins. Biophys J 2002; 83:1731-48. [PMID: 12324397 PMCID: PMC1302268 DOI: 10.1016/s0006-3495(02)73940-4] [Citation(s) in RCA: 378] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Protein stability and function relies on residues being in their appropriate ionization states at physiological pH. In situ residue pK(a)s also provides a sensitive measure of the local protein environment. Multiconformation continuum electrostatics (MCCE) combines continuum electrostatics and molecular mechanics force fields in Monte Carlo sampling to simultaneously calculate side chain ionization and conformation. The response of protein to charges is incorporated both in the protein dielectric constant (epsilon(prot)) of four and by explicit conformational changes. The pK(a) of 166 residues in 12 proteins was determined. The root mean square error is 0.83 pH units, and >90% have errors of <1 pH units whereas only 3% have errors >2 pH units. Similar results are found with crystal and solution structures, showing that the method's explicit conformational sampling reduces sensitivity to the initial structure. The outcome also changes little with protein dielectric constant (epsilon(prot) 4-20). Multiconformation continuum electrostatics titrations show coupling of conformational flexibility and changes in ionization state. Examples are provided where ionizable side chain position (protein G), Asn orientation (lysozyme), His tautomer distribution (RNase A), and phosphate ion binding (RNase A and H) change with pH. Disallowing these motions changes the calculated pK(a).
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28
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Gasque L, Bernès S, Ferrari R, Mendoza-Dı́az G. Cadmium complexation by aspartate. NMR studies and crystal structure of polymeric Cd(AspH)NO3. Polyhedron 2002. [DOI: 10.1016/s0277-5387(02)00871-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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29
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Johansson MU, Frick IM, Nilsson H, Kraulis PJ, Hober S, Jonasson P, Linhult M, Nygren PA, Uhlén M, Björck L, Drakenberg T, Forsén S, Wikström M. Structure, specificity, and mode of interaction for bacterial albumin-binding modules. J Biol Chem 2002; 277:8114-20. [PMID: 11751858 DOI: 10.1074/jbc.m109943200] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have determined the solution structure of an albumin binding domain of protein G, a surface protein of group C and G streptococci. We find that it folds into a left handed three-helix bundle similar to the albumin binding domain of protein PAB from Peptostreptococcus magnus. The two domains share 59% sequence identity, are thermally very stable, and bind to the same site on human serum albumin. The albumin binding site, the first determined for this structural motif known as the GA module, comprises residues spanning the first loop to the beginning of the third helix and includes the most conserved region of GA modules. The two GA modules have different affinities for albumin from different species, and their albumin binding patterns correspond directly to the host specificity of C/G streptococci and P. magnus, respectively. These studies of the evolution, structure, and binding properties of the GA module emphasize the power of bacterial adaptation and underline ecological and medical problems connected with the use of antibiotics.
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Affiliation(s)
- Maria U Johansson
- Department of Biophysical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
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30
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Abstract
The DSSP program assigns protein secondary structure to one of eight states. This discrete assignment cannot describe the continuum of thermal fluctuations. Hence, a continuous assignment is proposed. Technically, the continuum results from averaging over ten discrete DSSP assignments with different hydrogen bond thresholds. The final continuous assignment for a single NMR model successfully reflected the structural variations observed between all NMR models in the ensemble. The structural variations between NMR models were verified to correlate with thermal motion; these variations were captured by the continuous assignments. Because the continuous assignment reproduces the structural variation between many NMR models from one single model, functionally important variation can be extracted from a single X-ray structure. Thus, continuous assignments of secondary structure may affect future protein structure analysis, comparison, and prediction.
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Affiliation(s)
- Claus A F Andersen
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
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31
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Nelson MR, Thulin E, Fagan PA, Forsén S, Chazin WJ. The EF-hand domain: a globally cooperative structural unit. Protein Sci 2002; 11:198-205. [PMID: 11790829 PMCID: PMC2373453 DOI: 10.1110/ps.33302] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
EF-hand Ca(2+)-binding proteins participate in both modulation of Ca(2+) signals and direct transduction of the ionic signal into downstream biochemical events. The range of biochemical functions of these proteins is correlated with differences in the way in which they respond to the binding of Ca(2+). The EF-hand domains of calbindin D(9k) and calmodulin are homologous, yet they respond to the binding of calcium ions in a drastically different manner. A series of comparative analyses of their structures enabled the development of hypotheses about which residues in these proteins control the calcium-induced changes in conformation. To test our understanding of the relationship between protein sequence and structure, we specifically designed the F36G mutation of the EF-hand protein calbindin D(9k) to alter the packing of helices I and II in the apoprotein. The three-dimensional structure of apo F36G was determined in solution by nuclear magnetic resonance spectroscopy and showed that the design was successful. Surprisingly, significant structural perturbations also were found to extend far from the site of mutation. The observation of such long-range effects provides clear evidence that four-helix EF-hand domains should be treated as a single globally cooperative unit. A hypothetical mechanism for how the long-range effects are transmitted is described. Our results support the concept of energetic and structural coupling of the key residues that are crucial for a protein's fold and function.
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Affiliation(s)
- Melanie R Nelson
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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32
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Thermodynamics and Biochemical Equilibria. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50009-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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33
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Christova P, Cox JA, Craescu CT. Ion-induced conformational and stability changes in Nereis sarcoplasmic calcium binding protein: evidence that the APO state is a molten globule. Proteins 2000; 40:177-84. [PMID: 10842334 DOI: 10.1002/(sici)1097-0134(20000801)40:2<177::aid-prot10>3.0.co;2-t] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Nereis sarcoplasmic Ca(2+)-binding protein (NSCP) is a calcium buffer protein that binds Ca(2+) ions with high affinity but is also able to bind Mg(2+) ions with high positive cooperativity. We investigated the conformational and stability changes induced by the two metal ions. The thermal reversible unfolding, monitored by circular dichroism spectroscopy, shows that the thermal stability is maximum at neutral pH and increases in the order apo < Mg(2+) < Ca(2+). The stability against chemical denaturation (urea, guanidinium chloride) studied by circular dichroism or intrinsic fluorescence was found to have a similar ion dependence. To explore in more detail the structural basis of stability, we used the fluorescent probes to evaluate the hydrophobic surface exposure in the different ligation states. The apo-NSCP exhibits accessible hydrophobic surfaces, able to bind fluorescent probes, in clear contrast with denatured or Ca(2+)/Mg(2+)-bound states. Gel filtration experiments showed that, although the metal-bound NSCP has a hydrodynamic volume in agreement with the molecular mass, the volume of the apo form is considerably larger. The present results demonstrate that the apo state has many properties in common with the molten globule. The possible factors of the metal-dependent structural changes and stability are discussed.
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Affiliation(s)
- P Christova
- INSERM U350 & Institut Curie-Recherche, Orsay, France
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34
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Keller PA, Leach SP, Luu TT, Titmuss SJ, Griffith R. Development of computational and graphical tools for analysis of movement and flexibility in large molecules. J Mol Graph Model 2000; 18:235-41, 299. [PMID: 11021539 DOI: 10.1016/s1093-3263(00)00028-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
We developed a computer program for the calculation and display of the difference distance matrices (DDMs) of macromolecules that has the ability to compare multiple structures simultaneously. To demonstrate its use, a data set of atoms for superimposition of the HIV-1 reverse transcriptase enzyme was defined using the coordinates for the 21 available crystal structures of this enzyme and its complexes. The DDM technique for superimposition data set generation allows selection of atoms that are invariant in all structures, is free from user bias, and represents the most accurate and precise method of producing such subsets. Comparison of this technique was made against other published methods of generating superimposition data sets, and it was found that significant differences in magnitude and trends of atom movements are observed depending on which data set was used.
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Affiliation(s)
- P A Keller
- Department of Chemistry, University of Wollongong, Australia.
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35
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Brokx RD, Vogel HJ. Peptide and metal ion-dependent association of isolated helix-loop-helix calcium binding domains: studies of thrombic fragments of calmodulin. Protein Sci 2000; 9:964-75. [PMID: 10850806 PMCID: PMC2144632 DOI: 10.1110/ps.9.5.964] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Calmodulin (CaM), the ubiquitous, eukaryotic, bilobal calcium-binding regulatory protein, has been cleaved by thrombin to create two fragments. TM1 (1-106) and TM2 (107-148). NMR and CD results indicate that TMI and TM2 can associate in the presence of Ca2+ to form a complex similar to native CaM, even though the cleavage site is not in the linker region between two helix-loop-helix domains, but rather within an alpha-helix. Cadmium-113 NMR results show that this complex has enhanced metal-ion binding properties when compared to either TM1 or TM2 alone. This complex can bind several CaM-binding target peptides, as shown by gel bandshift assays, circular dichroism spectra, and 13C NMR spectra of biosynthetically methyl-13C-Met-labeled TM1 and TM2; moreover, gel bandshift assays show that the addition of a target peptide strengthens the interactions between TM1 and TM2 and increases the stability of the complex. Cadmium-113 NMR spectra indicate that the TM1:TM2 complex can also bind the antipsychotic drug trifluoperazine. However, in contrast to CaM:peptide complexes, the TM1:TM2:peptide complexes are disrupted by 4 M urea; moreover, TM1 and TM2 in combination are unable to activate CaM-dependent enzymes. This suggests that TM1:TM2 mixtures cannot bind target molecules as tightly as intact CaM, or perhaps that binding occurs but additional interactions with the target enzymes that are necessary for proper activation are perturbed by the proteolytic cleavage. The results presented here reflect the importance of the existence of helix-loop-helix Ca2+-binding domains in pairs in proteins such as CaM, and extend the understanding of the association of such domains in this class of proteins in general.
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Affiliation(s)
- R D Brokx
- Department of Biological Sciences, University of Calgary, Alberta, Canada
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36
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van Dongen MJ, Cederberg A, Carlsson P, Enerbäck S, Wikström M. Solution structure and dynamics of the DNA-binding domain of the adipocyte-transcription factor FREAC-11. J Mol Biol 2000; 296:351-9. [PMID: 10669593 DOI: 10.1006/jmbi.1999.3476] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Transcription factors of the forkhead type share a highly conserved DNA-binding domain of about 100 amino acid residues. FREAC-11, expressed in adipocytes, belongs to this class. Here, we report on NMR studies that established the three-dimensional structure of the FREAC-11, DNA-binding domain. Although apparent similarities to the structures of other members within the forkhead family are observed, the structure also reveals some remarkable differences. Along with the complementary dynamics, the data provide insight into the fundamentals of sequence specificity within a highly conserved motif.
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Affiliation(s)
- M J van Dongen
- Department of Structural Chemistry, Pharmacia and Upjohn, Nordenflychtsvägen 62:5, Stockholm, S-11287, Sweden.
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37
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Malmendal A, Evenäs J, Forsén S, Akke M. Structural dynamics in the C-terminal domain of calmodulin at low calcium levels. J Mol Biol 1999; 293:883-99. [PMID: 10543974 DOI: 10.1006/jmbi.1999.3188] [Citation(s) in RCA: 137] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Calmodulin undergoes Ca2+-induced structural rearrangements that are intimately coupled to the regulation of numerous cellular processes. The C-terminal domain of calmodulin has previously been observed to exhibit conformational exchange in the absence of Ca2+. Here, we characterize further the conformational dynamics in the presence of low concentrations of Ca2+ using 15N spin relaxation experiments. The analysis included 1H-15N dipolar/15N chemical shift anisotropy interference cross-correlation relaxation rates to improve the description of the exchange processes, as well as the picosecond to nanosecond dynamics. Conformational transitions on microsecond to millisecond time scales were revealed by exchange contributions to the transverse auto-relaxation rates. In order to separate the effects of Ca2+ exchange from intramolecular conformational exchange processes in the apo state, transverse auto-relaxation rates were measured at different concentrations of free Ca2+. The results reveal a Ca2+-dependent contribution due mainly to exchange between the apo and (Ca2+)1 states with an apparent Ca2+ off-rate of approximately 5115 s(-1), as well as Ca2+-independent contributions due to conformational exchange within the apo state. 15N chemical shift differences estimated from the exchange data suggest that the first Ca2+ binds preferentially to loop IV. Thus, characterization of chemical exchange as a function of Ca2+ concentration has enabled the extraction of unique information on the rapidly exchanging and weakly populated (<10 %) (Ca2+)1 state that is otherwise inaccessible to direct study due to strongly cooperative Ca2+ binding. The conformational exchange within the apo state appears to involve transitions between a predominantly populated closed conformation and a smaller population of more open conformations. The picosecond to nanosecond dynamics of the apo state are typical of a well-folded protein, with reduced amplitudes of motions in the helical segments, but with significant flexibility in the Ca2+-binding loops. Comparisons with order parameters for skeletal troponin C and calbindin D9k reveal key structural and dynamical differences that correlate with the different Ca2+-binding properties of these proteins.
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Affiliation(s)
- A Malmendal
- Physical Chemistry 2, Lund University, Lund, S-221 00, Sweden
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38
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Chazin W, Veenstra TD. Determination of the metal-binding cooperativity of wild-type and mutant calbindin D9K by electrospray ionization mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 1999; 13:548-555. [PMID: 10204248 DOI: 10.1002/(sici)1097-0231(19990330)13:6<548::aid-rcm523>3.0.co;2-u] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Since the initial reports showing the ability of electrospray ionization mass spectrometry (ESI-MS) to study intact noncovalent biomolecular complexes, an increasing number of uses for this technique in studying biochemical systems is emerging. We have investigated the ability of ESI-MS to characterize the metal-binding properties of calcium (Ca2+) binding proteins by studying the incorporation of Ca2+ and cadmium (Cd2+) into wild-type and mutant calbindin D9K. ESI-MS showed that wild-type calbindin D9K binds two Ca2+ ions with similar affinities while the binding of two Cd2+ ions is sequential, as is the binding of the two Ca2+ or Cd2+ ions to the N56A mutant of calbindin. The binding of Ca2+ to the wild-type protein was clearly seen to be cooperative. These results demonstrate the potential efficacy of ESI-MS to discriminate between cooperative and independent site metal binding to metalloproteins.
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Affiliation(s)
- W Chazin
- Department of Molecular Biology, Scripps Research Institute, La Jolla, California 92037, USA
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39
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Biekofsky RR, Feeney J. Cooperative cyclic interactions involved in metal binding to pairs of sites in EF-hand proteins. FEBS Lett 1998; 439:101-6. [PMID: 9849887 DOI: 10.1016/s0014-5793(98)01349-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
This study focuses on a closed net of electron-pair donor-acceptor interactions, present in the core of all metal-bound EF-hand pairs, that link both metal ions across a short two-stranded beta-sheet. A molecular model based on the above cycle of interactions was studied using semi-empirical molecular orbital quantum mechanical methods. The calculations indicate that the interactions in the model cycle are cooperative, that is, that the interaction energy of the cyclic structure is greater than that of the sum of isolated interactions between its components. The cooperativity in this cycle can be attributed to an increase in the stability of the interactions resulting from a mutual polarisation of the associated groups. The predicted polarisation of the amide groups in the cycle is in agreement with experimental NMR 15N deshielding observed for these amide groups upon metal binding. Experimental observations of strengthening of the beta-sheet hydrogen bonds are also consistent with the model calculations. By this mechanism, the binding of the first metal ion would enhance the binding of the second metal ion, and thus, the intradomain cooperativity in cation binding of calmodulin and related EF-hand proteins can be ascribed, at least partly, to this short-range molecular mechanism.
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Affiliation(s)
- R R Biekofsky
- Molecular Structure Division, National Institute for Medical Research, London, UK.
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40
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41
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Evenäs J, Malmendal A, Thulin E, Carlström G, Forsén S. Ca2+ binding and conformational changes in a calmodulin domain. Biochemistry 1998; 37:13744-54. [PMID: 9753463 DOI: 10.1021/bi9806448] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Calcium activation of the C-terminal domain of calmodulin was studied using 1H and 15N NMR spectroscopy. The important role played by the conserved bidentate glutamate Ca2+ ligand in the binding loops is emphasized by the striking effects resulting from a mutation of this glutamic acid to a glutamine, i.e. E104Q in loop III and E140Q in loop IV. The study involves determination of Ca2+ binding constants, assignments, and structural characterizations of the apo, (Ca2+)1, and (Ca2+)2 states of the E104Q mutant and comparisons to the wild-type protein and the E140Q mutant [Evenäs et al. (1997) Biochemistry 36, 3448-3457]. NMR titration data show sequential Ca2+ binding in the E104Q mutant. The first Ca2+ binds to loop IV and the second to loop III, which is the order reverse to that observed for the E140Q mutant. In both mutants, the major structural changes occur upon Ca2+ binding to loop IV, which implies a different response to Ca2+ binding in the N- and C-terminal EF-hands. Spectral characteristics show that the (Ca2+)1 and (Ca2+)2 states of the E104Q mutant undergo global exchange on a 10-100 micros time scale between conformations seemingly similar to the closed and open structures of this domain in wild-type calmodulin, paralleling earlier observations for the (Ca2+)2 state of the E140Q mutant, indicating that both glutamic acid residues, E104 and E140, are required for stabilization of the open conformation in the (Ca2+)2 state. To verify that the NOE constraints cannot be fulfilled in a single structure, solution structures of the (Ca2+)2 state of the E104Q mutant are calculated. Within the ensemble of structures the precision is good. However, the clearly dynamic nature of the state, a large number of violated distance restraints, ill-defined secondary structural elements, and comparisons to the structures of calmodulin indicate that the ensemble does not provide a good picture of the (Ca2+)2 state of the E104Q mutant but rather represents the distance-averaged structure of at least two distinct different conformations.
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Affiliation(s)
- J Evenäs
- Physical Chemistry 2, Lund University, Sweden.
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42
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Spassov V, Bashford D. Electrostatic coupling to pH-titrating sites as a source of cooperativity in protein-ligand binding. Protein Sci 1998; 7:2012-25. [PMID: 9761483 PMCID: PMC2144168 DOI: 10.1002/pro.5560070918] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This paper describes an alternative mechanism for the cooperative binding of charged ligands to proteins. The ligand-binding sites are electrostatically coupled to protein side chains that can undergo protonation and deprotonation. The binding of one ligand alters the protein's protonation equilibrium in a manner that makes the the binding of the second ligand more favorable. This mechanism requires no conformational change to produce a cooperative effect, although it is not exclusive of conformational change. We present a theoretical description of the mechanism, and calculations on three kinds of systems: A model system containing one protonation site and two ligand-binding sites; a model system containing two protonation sites and two ligand-binding sites; and calbindin D9k, which contains two Ca2+-binding sites and 30 protonation sites. For the one-protonation-site model, it is shown that the influence of the protonation site can only be cooperative. The competition of this effect with the anticooperative effect of ligand-ligand repulsion is studied in detail. For the two-protonation site model, the effect can be either cooperative or, in special cases, anticooperative. For calbindin D9k, the calculations predict that six protonation sites in or near the ligand-binding sites make a cooperative contribution that approximately cancels the anticooperative effect of Ca2+-Ca2+ repulsion, accounting for more than half of the total cooperative effect that is needed to overcome repulsion and produce the net cooperativity observed experimentally. We argue that cooperative mechanisms of the kind described here are likely when there is more than one ligand-binding site in a protein domain.
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Affiliation(s)
- V Spassov
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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43
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Muranyi A, Finn BE, Gippert GP, Forsén S, Stenflo J, Drakenberg T. Solution structure of the N-terminal EGF-like domain from human factor VII. Biochemistry 1998; 37:10605-15. [PMID: 9692950 DOI: 10.1021/bi980522f] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Blood coagulation is initiated by Ca(2+)-dependent binding of coagulation factor VIIa (FVIIa) to its cofactor, tissue factor (TF). The TF:FVIIa complex activates factors IX and X, ultimately leading to the formation of thrombin and the coagulation of blood. FVII consists of an N-terminal gamma-carboxyglutamic-acid-containing (Gla) domain followed by two epidermal growth factor (EGF) like domains, the first of which can bind one Ca2+ ion (Kd approximately 150 microM) and a C-terminal serine protease domain. Using 1H nuclear magnetic resonance spectroscopy, we have determined the solution structure of a synthetic N-terminal EGF-like domain (EGF1) of human FVII (residues 45-85) in the absence of Ca2+. A comparison of this structure of apo EGF1 with the Ca(2+)-bound EGF1 in the complex of FVIIa and TF [Banner, D. W., et al. (1996) Nature 380, 41-46] suggests that the structural changes in the EGF1 domain upon Ca2+ binding are minor and are concentrated near the Ca(2+)-binding site, which is facing away from the TF interaction surface. Amino acid side chains that are crucial for the binding of FVII to TF show a similar conformation in both structures and are therefore unlikely to directly influence the Ca(2+)-dependent binding of FVII to TF. As Ca2+ binding to EGF1 does not lead to a conformational change in the residues constituting the interaction surface for binding to TF, our results are consistent with the idea that the altered orientation between the Gla and EGF1 domains that result from Ca2+ binding is responsible for the increased affinity of FVII/FVIIa for TF.
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Affiliation(s)
- A Muranyi
- Physical Chemistry 2, Lund University, Sweden.
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44
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Kragelund BB, Jönsson M, Bifulco G, Chazin WJ, Nilsson H, Finn BE, Linse S. Hydrophobic core substitutions in calbindin D9k: effects on Ca2+ binding and dissociation. Biochemistry 1998; 37:8926-37. [PMID: 9636034 DOI: 10.1021/bi9726436] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hydrophobic core residues have a marked influence on the Ca2+-binding properties of calbindin D9k, even though there are no direct contacts between these residues and the bound Ca2+ ions. Eleven different mutants with substitutions in the hydrophobic core were produced, and their equilibrium Ca2+-binding constants measured from Ca2+ titrations in the presence of chromophoric chelators. The Ca2+-dissociation rate constants were estimated from Ca2+ titrations followed by 1H NMR1 and were measured more accurately using stopped-flow fluorescence. The parameters were measured at four KCl concentrations to assess the salt dependence of the perturbations. The high similarity between the NMR spectra of mutants and wild-type calbindin D9k suggests that the structure is largely unperturbed by the substitutions. More detailed NMR investigations of the mutant in which Val61 is substituted by Ala showed that the mutation causes only very minimal perturbations in the immediate vicinity of residue 61. Substitutions of alanines or glycines for bulky residues in the center of the core were found to have significant effects on both Ca2+ affinity and dissociation rates. These substitutions caused a reduction in affinity and an increase in off-rate. Small effects, both increases and decreases, were observed for substitutions involving residues far from the Ca2+ sites and toward the outer part of the hydrophobic core. The mutant with the substitution Phe66 --> Trp behaved differently from all other mutants, and displayed a 25-fold increase in overall affinity of binding two Ca2+ ions and a 6-fold reduction in calcium dissociation rate. A strong correlation (R = 0.94) was found between the observed Ca2+-dissociation rates and affinities, as well as between the salt dependence of the off-rate and the distance to the nearest Ca2+-coordinating atom. There was also a strong correlation (R = 0.95) between the Ca2+ affinity and stability of the Ca2+ state and a correlation (R = 0. 69) between the Ca2+ affinity and stability of the apo state, as calculated from the results in the present and preceding paper in this issue [Julenius, K., Thulin, E., Linse, S., and Finn, B. E. (1998) Biochemistry 37, 8915-8925]. The change in salt dependencies of koff and cooperativity were most pronounced for residues completely buried in the core of the protein (solvent accessible surface area approximately 0). Altogether, the results suggest that the hydrophobic core residues promote Ca2+ binding both by contributing to the preformation of the Ca2+ sites in the apo state and by preferentially stabilizing the Ca2+-bound state.
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Affiliation(s)
- B B Kragelund
- Physical Chemistry 2, Lund University, Chemical Centre, Sweden
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45
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Biekofsky RR, Martin SR, Browne JP, Bayley PM, Feeney J. Ca2+ coordination to backbone carbonyl oxygen atoms in calmodulin and other EF-hand proteins: 15N chemical shifts as probes for monitoring individual-site Ca2+ coordination. Biochemistry 1998; 37:7617-29. [PMID: 9585577 DOI: 10.1021/bi9800449] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Examination of the NMR 15N chemical shifts of a number of EF-hand proteins shows that the shift value for the amido nitrogen of the residue in position 8 of a canonical EF-hand loop (or position 10 of a pseudo EF-hand loop) provides a good indication of metal occupation of that site. The NH of the residue in position 8 is covalently bonded to the carbonyl of residue 7, the only backbone carbonyl that coordinates to the metal ion in a canonical EF-hand loop. Upon metal coordination to this carbonyl, there is an appreciable deshielding of the 15N nucleus at position 8 (+4 to +8 ppm) due to the polarization of the O(7)=C(7)-N(8) amido group and the corresponding reduction in the electron density of the nitrogen atom. This deshielding effect is effectively independent of the binding of metal to the other site of an EF-hand pair, allowing the 15N shifts to be used as probes for site-specific occupancy of metal binding sites. In addition, a Ca2+-induced change in side-chain Halpha-Calpha-Cbeta-Hbeta torsion angle for isoleucine or valine residues in position 8 can also contribute to the deshielding of the amide 15N nucleus. This conformational effect occurs only in sites I or III and takes place upon binding a Ca2+ ion to the other site of an EF-hand pair (site II or IV) regardless of whether the first site is occupied. The magnitude of this effect is in the range +5 to +7 ppm. A Ca2+ titration of 15N-labeled apo-calmodulin was performed using 2D 1H-15N HSQC NMR spectra. The changes in the 15N chemical shifts and intensities for the peaks corresponding to the NH groups of residues in position 8 of the EF-hand loops allowed the amount of metal bound at sites II, III and IV to be monitored directly at partial degrees of saturation. The peak corresponding to site I could only be monitored at the beginning and end of the titration because of line broadening effects in the intermediate region of the titration. Sites III and IV both titrate preferentially and the results demonstrate clearly that sites in either domain fill effectively in parallel, consistent with a significant positive intradomain cooperativity of calcium binding.
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Affiliation(s)
- R R Biekofsky
- Molecular Structure Division, Physical Biochemistry Division, National Institute for Medical Research, London, U.K
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46
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Mossing MC. Solution structure and dynamics of a designed monomeric variant of the lambda Cro repressor. Protein Sci 1998; 7:983-93. [PMID: 9568905 PMCID: PMC2143973 DOI: 10.1002/pro.5560070416] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The solution structure of a monomeric variant of the lambda Cro repressor has been determined by multidimensional NMR. Cro K56[DGEVK] differs from wild-type Cro by the insertion of five amino acids at the center of the dimer interface. 1H and 15N resonances for 70 of the 71 residues have been assigned. Thirty-two structures were calculated by hybrid distance geometry/simulated annealing methods using 463 NOE-distance restraints, 26 hydrogen-bond, and 39 dihedral-angle restraints. The root-mean-square deviation (RMSD) from the average structure for atoms in residues 3-60 is 1.03 +/- 0.44 A for the peptide backbone and 1.6 +/- 0.73 A for all nonhydrogen atoms. The overall structure conforms very well to the original design. Although the five inserted residues form a beta hairpin as expected, this engineered turn as well as other turns in the structure are not well defined by the NMR data. Dynamics studies of backbone amides reveal T1/T2 ratios of residues in the alpha2-alpha3, beta2-beta3, and engineered turn that are reflective of chemical exchange or internal motion. The solution structure and dynamics are discussed in light of the conformational variation that has been observed in other Cro structures, and the importance of flexibility in DNA recognition.
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Affiliation(s)
- M C Mossing
- Department of Biological Sciences, University of Notre Dame, Indiana 46556, USA.
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47
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Malmendal A, Carlstrom G, Hambraeus C, Drakenberg T, Forsen S, Akke M. Sequence and context dependence of EF-hand loop dynamics. An 15N relaxation study of a calcium-binding site mutant of calbindin D9k. Biochemistry 1998; 37:2586-95. [PMID: 9485409 DOI: 10.1021/bi971798a] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The influence of amino acid sequence and structural context on the backbone dynamics of EF-hand calcium-binding loops was investigated using 15N spin relaxation measurements on the calcium-free state of the calbindin D9k mutant (A14D+A15Delta+P20Delta+N21G+P43M), in which the N-terminal pseudo-EF-hand loop, characteristic of S100 proteins, was engineered so as to conform with the C-terminal consensus EF-hand loop. The results were compared to a previous study of the apo state of the wild-type-like P43G calbindin D9k mutant. In the helical regions, the agreement with the P43G data is excellent, indicating that the structure and dynamics of the protein core are unaffected by the substitutions in the N-terminal loop. In the calcium-binding loops, the flexibility is drastically decreased compared to P43G, with the modified N-terminal loop showing a motional restriction comparable to that of the surrounding helixes. As in P43G, the motions in the C-terminal loop are less restricted than in the N-terminal loop. Differences in key hydrogen-bonding interactions correlate well with differences in dynamics and offer insights into the relationship between structure and dynamics of these EF-hand loops. It appears that the entire N-terminal EF-hand is built to form a rigid structure that allows calcium binding with only minor rearrangements and that the structural and dynamical properties of the entire EF-hand--rather than the loop sequence per se--is the major determinant of loop flexibility in this system.
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Affiliation(s)
- A Malmendal
- Physical Chemistry 2, Lund University, P.O. Box 124, S-221 00 Lund, Sweden.
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48
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Sastry M, Ketchem RR, Crescenzi O, Weber C, Lubienski MJ, Hidaka H, Chazin WJ. The three-dimensional structure of Ca(2+)-bound calcyclin: implications for Ca(2+)-signal transduction by S100 proteins. Structure 1998; 6:223-31. [PMID: 9519412 DOI: 10.1016/s0969-2126(98)00023-9] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND Calcyclin is a member of the S100 subfamily of EF-hand Ca(2+)-binding proteins. This protein has implied roles in the regulation of cell growth and division, exhibits deregulated expression in association with cell transformation, and is found in high abundance in certain breast cancer cell lines. The novel homodimeric structural motif first identified for apo calcyclin raised the possibility that S100 proteins recognize their targets in a manner that is distinctly different from that of the prototypical EF-hand Ca2+ sensor, calmodulin. The NMR solution structure of Ca(2+)-bound calcyclin has been determined in order to identify Ca(2+)-induced structural changes and to obtain insights into the mechanism of Ca(2+)-triggered target protein recognition. RESULTS The three-dimensional structure of Ca(2+)-bound calcyclin was calculated with 1372 experimental constraints, and is represented by an ensemble of 20 structures that have a backbone root mean square deviation of 1.9 A for the eight helices. Ca(2+)-bound calcyclin has the same symmetric homodimeric fold as observed for the apo protein. The helical packing within the globular domains and the subunit interface also change little upon Ca2+ binding. A distinct homology was found between the Ca(2+)-bound states of the calcyclin subunit and the monomeric S100 protein calbindin D9k. CONCLUSIONS Only very modest Ca(2+)-induced changes are observed in the structure of calcyclin, in sharp contrast to the domain-opening that occurs in calmodulin and related Ca(2+)-sensor proteins. Thus, calcyclin, and by inference other members of the S100 family, must have a different mode for transducing Ca2+ signals and recognizing target proteins. This proposal raises significant questions concerning the purported roles of S100 proteins as Ca2+ sensors.
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Affiliation(s)
- M Sastry
- Department of Molecular Biology (MB-9), Scripps Research Institute, La Jolla, California 92037, USA
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49
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Nelson MR, Chazin WJ. An interaction-based analysis of calcium-induced conformational changes in Ca2+ sensor proteins. Protein Sci 1998; 7:270-82. [PMID: 9521102 PMCID: PMC2143906 DOI: 10.1002/pro.5560070206] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Calcium sensor proteins translate transient increases in intracellular calcium levels into metabolic or mechanical responses, by undergoing dramatic conformational changes upon Ca2+ binding. A detailed analysis of the calcium binding-induced conformational changes in the representative calcium sensors calmodulin (CaM) and troponin C was performed to obtain insights into the underlying molecular basis for their response to the binding of calcium. Distance difference matrices, analysis of interresidue contacts, comparisons of interhelical angles, and inspection of structures using molecular graphics were used to make unbiased comparisons of the various structures. The calcium-induced conformational changes in these proteins are dominated by reorganization of the packing of the four helices within each domain. Comparison of the closed and open conformations confirms that calcium binding causes opening within each of the EF-hands. A secondary analysis of the conformation of the C-terminal domain of CaM (CaM-C) clearly shows that CaM-C occupies a closed conformation in the absence of calcium that is distinct from the semi-open conformation observed in the C-terminal EF-hand domains of myosin light chains. These studies provide insight into the structural basis for these changes and into the differential response to calcium binding of various members of the EF-hand calcium-binding protein family. Factors contributing to the stability of the Ca2+-loaded open conformation are discussed, including a new hypothesis that critical hydrophobic interactions stabilize the open conformation in Ca2+ sensors, but are absent in "non-sensor" proteins that remain closed upon Ca2+ binding. A role for methionine residues in stabilizing the open conformation is also proposed.
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Affiliation(s)
- M R Nelson
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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Ketchem R, Roux B, Cross T. High-resolution polypeptide structure in a lamellar phase lipid environment from solid state NMR derived orientational constraints. Structure 1997; 5:1655-69. [PMID: 9438865 DOI: 10.1016/s0969-2126(97)00312-2] [Citation(s) in RCA: 233] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Solid-state nuclear magnetic resonance (NMR) spectroscopy provides novel structural constraints from uniformly aligned samples. These orientational constraints orient specific atomic sites with respect to the magnetic field direction and the unique molecular axis of alignment. Solid-state NMR is uniquely and ideally suited for providing such structural constraints on polypeptides and proteins in a lamellar phase lipid environment. Membrane protein structure represents a great challenge for structural biologists; a new approach for characterizing high resolution three-dimensional structure in such an environment is needed. RESULTS The optimal use of orientational constraints for defining three-dimensional structures is demonstrated with the elucidation of the gramicidin A channel structure at high resolution. Initial structures are refined against both the experimental constraints and the CHARMM energy using a novel simulated-annealing protocol to define torsion angle solutions with an error bar of approximately +/- 5 degrees. CONCLUSIONS This analysis results in the determination of a high-resolution, time averaged structure of gramicidin A obtained in a lipid bilayer environment above the gel-to-liquid crystalline phase transition temperature. It is demonstrated that solid-state NMR can be used to establish polypeptide, and potentially protein, structures in such an environment. Furthermore, this high-resolution structure is demonstrated to provide new insights into polypeptide function. For the gramicidin A channel the roles of the indole groups that facilitate ion transport and details of the cation solvation environment provided by the amide oxygens are characterized.
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Affiliation(s)
- R Ketchem
- Center for Interdisciplinary Magnetic Resonance at the National High Magnetic Field Laboratory, Florida State University, Tallahassee 32306-4005, USA
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