1
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A Free-Energy Landscape Analysis of Calmodulin Obtained from an NMR Data-Utilized Multi-Scale Divide-and-Conquer Molecular Dynamics Simulation. Life (Basel) 2021; 11:life11111241. [PMID: 34833117 PMCID: PMC8617919 DOI: 10.3390/life11111241] [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: 09/30/2021] [Revised: 11/08/2021] [Accepted: 11/10/2021] [Indexed: 11/16/2022] Open
Abstract
Calmodulin (CaM) is a multifunctional calcium-binding protein, which regulates a variety of biochemical processes. CaM acts through its conformational changes and complex formation with its target enzymes. CaM consists of two globular domains (N-lobe and C-lobe) linked by an extended linker region. Upon calcium binding, the N-lobe and C-lobe undergo local conformational changes, followed by a major conformational change of the entire CaM to wrap the target enzyme. However, the regulation mechanisms, such as allosteric interactions, which regulate the large structural changes, are still unclear. In order to investigate the series of structural changes, the free-energy landscape of CaM was obtained by multi-scale divide-and-conquer molecular dynamics (MSDC-MD). The resultant free-energy landscape (FEL) shows that the Ca2+ bound CaM (holo-CaM) would take an experimentally famous elongated structure, which can be formed in the early stage of structural change, by breaking the inter-domain interactions. The FEL also shows that important interactions complete the structural change from the elongated structure to the ring-like structure. In addition, the FEL might give a guiding principle to predict mutational sites in CaM. In this study, it was demonstrated that the movement process of macroscopic variables on the FEL may be diffusive to some extent, and then, the MSDC-MD is suitable to the parallel computation.
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2
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Phospholipases C and D and Their Role in Biotic and Abiotic Stresses. PLANTS 2021; 10:plants10050921. [PMID: 34064485 PMCID: PMC8148002 DOI: 10.3390/plants10050921] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 04/28/2021] [Accepted: 04/29/2021] [Indexed: 02/03/2023]
Abstract
Plants, as sessile organisms, have adapted a fine sensing system to monitor environmental changes, therefore allowing the regulation of their responses. As the interaction between plants and environmental changes begins at the surface, these changes are detected by components in the plasma membrane, where a molecule receptor generates a lipid signaling cascade via enzymes, such as phospholipases (PLs). Phospholipids are the key structural components of plasma membranes and signaling cascades. They exist in a wide range of species and in different proportions, with conversion processes that involve hydrophilic enzymes, such as phospholipase-C (PLC), phospholipase-D (PLD), and phospholipase-A (PLA). Hence, it is suggested that PLC and PLD are highly conserved, compared to their homologous genes, and have formed clusters during their adaptive history. Additionally, they generate responses to different functions in accordance with their protein structure, which should be reflected in specific signal transduction responses to environmental stress conditions, including innate immune responses. This review summarizes the phospholipid systems associated with signaling pathways and the innate immune response.
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3
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Smith LJ, Green CW, Redfield C. The 'Shape-Shifter' Peptide from the Disulphide Isomerase PmScsC Shows Context-Dependent Conformational Preferences. Biomolecules 2021; 11:biom11050642. [PMID: 33926076 PMCID: PMC8146718 DOI: 10.3390/biom11050642] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 04/16/2021] [Accepted: 04/21/2021] [Indexed: 11/16/2022] Open
Abstract
Multiple crystal structures of the homo-trimeric protein disulphide isomerase PmScsC reveal that the peptide which links the trimerization stalk and catalytic domain can adopt helical, β-strand and loop conformations. This region has been called a 'shape-shifter' peptide. Characterisation of this peptide using NMR experiments and MD simulations has shown that it is essentially disordered in solution. Analysis of the PmScsC crystal structures identifies the role of intermolecular contacts, within an assembly of protein molecules, in stabilising the different linker peptide conformations. These context-dependent conformational properties may be important functionally, allowing for the binding and disulphide shuffling of a variety of protein substrates to PmScsC. They also have a relevance for our understanding of protein aggregation and misfolding showing how intermolecular quaternary interactions can lead to β-sheet formation by a sequence that in other contexts adopts a helical structure. This 'shape-shifting' peptide region within PmScsC is reminiscent of one-to-many molecular recognition features (MoRFs) found in intrinsically disordered proteins which are able to adopt different conformations when they fold upon binding to their protein partners.
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Affiliation(s)
- Lorna J. Smith
- Department of Chemistry, University of Oxford, Oxford OX1 3QR, UK;
- Correspondence: (L.J.S.); (C.R.)
| | - Chloe W. Green
- Department of Chemistry, University of Oxford, Oxford OX1 3QR, UK;
| | - Christina Redfield
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK
- Correspondence: (L.J.S.); (C.R.)
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4
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Jeon J, Yau WM, Tycko R. Millisecond Time-Resolved Solid-State NMR Reveals a Two-Stage Molecular Mechanism for Formation of Complexes between Calmodulin and a Target Peptide from Myosin Light Chain Kinase. J Am Chem Soc 2020; 142:21220-21232. [PMID: 33280387 DOI: 10.1021/jacs.0c11156] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Calmodulin (CaM) mediates a wide range of biological responses to changes in intracellular Ca2+ concentrations through its calcium-dependent binding affinities to numerous target proteins. Binding of two Ca2+ ions to each of the two four-helix-bundle domains of CaM results in major conformational changes that create a potential binding site for the CaM binding domain of a target protein, which also undergoes major conformational changes to form the complex with CaM. Details of the molecular mechanism of complex formation are not well established, despite numerous structural, spectroscopic, thermodynamic, and kinetic studies. Here, we report a study of the process by which the 26-residue peptide M13, which represents the CaM binding domain of skeletal muscle myosin light chain kinase, forms a complex with CaM in the presence of excess Ca2+ on the millisecond time scale. Our experiments use a combination of selective 13C labeling of CaM and M13, rapid mixing of CaM solutions with M13/Ca2+ solutions, rapid freeze-quenching of the mixed solutions, and low-temperature solid state nuclear magnetic resonance (ssNMR) enhanced by dynamic nuclear polarization. From measurements of the dependence of 2D 13C-13C ssNMR spectra on the time between mixing and freezing, we find that the N-terminal portion of M13 converts from a conformationally disordered state to an α-helix and develops contacts with the C-terminal domain of CaM in about 2 ms. The C-terminal portion of M13 becomes α-helical and develops contacts with the N-terminal domain of CaM more slowly, in about 8 ms. The level of structural order in the CaM/M13/Ca2+ complexes, indicated by 13C ssNMR line widths, continues to increase beyond 27 ms.
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Affiliation(s)
- Jaekyun Jeon
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, United States
| | - Wai-Ming Yau
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, United States
| | - Robert Tycko
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, United States
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5
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Harborne SPD, Kunji ERS. Calcium-regulated mitochondrial ATP-Mg/P i carriers evolved from a fusion of an EF-hand regulatory domain with a mitochondrial ADP/ATP carrier-like domain. IUBMB Life 2018; 70:1222-1232. [PMID: 30281880 PMCID: PMC6283063 DOI: 10.1002/iub.1931] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Revised: 07/19/2018] [Accepted: 07/19/2018] [Indexed: 02/02/2023]
Abstract
The mitochondrial ATP-Mg/Pi carrier is responsible for the calcium-dependent regulation of adenosine nucleotide concentrations in the mitochondrial matrix, which allows mitochondria to respond to changing energy requirements of the cell. The carrier is expressed in mitochondria of fungi, plants and animals and belongs to the family of mitochondrial carriers. The carrier is unusual as it consists of three separate domains: (i) an N-terminal regulatory domain with four calcium-binding EF-hands similar to calmodulin, (ii) a loop domain containing an amphipathic α-helix and (iii) a mitochondrial carrier domain related to the mitochondrial ADP/ATP carrier. This striking example of three domains coming together from different origins to provide new functions represents an interesting quirk of evolution. In this review, we outline how the carrier was identified and how its physiological role was established with a focus on human isoforms. We exploit the sequence and structural information of the domains to explore the similarities and differences to their closest counterparts; mitochondrial ADP/ATP carriers and proteins with four EF-hands. We discuss how their combined function has led to a mechanism for calcium-regulated transport of adenosine nucleotides. Finally, we compare the ATP-Mg/Pi carrier with the mitochondrial aspartate/glutamate carrier, the only other mitochondrial carrier regulated by calcium, and we will argue that they have arisen by convergent rather than divergent evolution. © 2018 The Authors. IUBMB Life published by Wiley Periodicals, Inc. on behalf of International Union of Biochemistry and Molecular Biology, 70(12):1222-1232, 2018.
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Affiliation(s)
- Steven P. D. Harborne
- School of Biomedical Sciences and Astbury Centre for Structural Molecular BiologyUniversity of LeedsLeedsLS2 9JTUK
| | - Edmund R. S. Kunji
- Medical Research Council Mitochondrial Biology UnitUniversity of CambridgeCambridgeCB2 0XYUK
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6
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Westerlund AM, Delemotte L. Effect of Ca2+ on the promiscuous target-protein binding of calmodulin. PLoS Comput Biol 2018; 14:e1006072. [PMID: 29614072 PMCID: PMC5898786 DOI: 10.1371/journal.pcbi.1006072] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 04/13/2018] [Accepted: 03/07/2018] [Indexed: 01/05/2023] Open
Abstract
Calmodulin (CaM) is a calcium sensing protein that regulates the function of a large number of proteins, thus playing a crucial part in many cell signaling pathways. CaM has the ability to bind more than 300 different target peptides in a Ca2+-dependent manner, mainly through the exposure of hydrophobic residues. How CaM can bind a large number of targets while retaining some selectivity is a fascinating open question. Here, we explore the mechanism of CaM selective promiscuity for selected target proteins. Analyzing enhanced sampling molecular dynamics simulations of Ca2+-bound and Ca2+-free CaM via spectral clustering has allowed us to identify distinct conformational states, characterized by interhelical angles, secondary structure determinants and the solvent exposure of specific residues. We searched for indicators of conformational selection by mapping solvent exposure of residues in these conformational states to contacts in structures of CaM/target peptide complexes. We thereby identified CaM states involved in various binding classes arranged along a depth binding gradient. Binding Ca2+ modifies the accessible hydrophobic surface of the two lobes and allows for deeper binding. Apo CaM indeed shows shallow binding involving predominantly polar and charged residues. Furthermore, binding to the C-terminal lobe of CaM appears selective and involves specific conformational states that can facilitate deep binding to target proteins, while binding to the N-terminal lobe appears to happen through a more flexible mechanism. Thus the long-ranged electrostatic interactions of the charged residues of the N-terminal lobe of CaM may initiate binding, while the short-ranged interactions of hydrophobic residues in the C-terminal lobe of CaM may account for selectivity. This work furthers our understanding of the mechanism of CaM binding and selectivity to different target proteins and paves the way towards a comprehensive model of CaM selectivity.
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Affiliation(s)
- Annie M. Westerlund
- Science for Life Laboratory, Department of Applied Physics, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Lucie Delemotte
- Science for Life Laboratory, Department of Applied Physics, KTH Royal Institute of Technology, Stockholm, Sweden
- * E-mail:
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7
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He YY, Wang YB, Zheng Z, Liu FM, An ML, He XD, Qu CF, Li LL, Miao JL. Cloning and Stress-Induced Expression Analysis of Calmodulin in the Antarctic Alga Chlamydomonas sp. ICE-L. Curr Microbiol 2017; 74:921-929. [PMID: 28516199 DOI: 10.1007/s00284-017-1263-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 05/06/2017] [Indexed: 12/28/2022]
Abstract
Calmodulin (CaM) is a Ca2+-binding protein that plays a role in several Ca2+ signaling pathways, which dynamically regulates the activities of hundreds of proteins. The ice alga Chlamydomonas sp. ICE-L, which has the ability to adapt to extreme polar conditions, is a crucial primary producer in Antarctic ecosystem. This study hypothesized that Cam helps the ICE-L to adapt to the fluctuating conditions in the polar environment. It first verified the overall length of Cam, through RT-PCR and RACE-PCR, based on partial Cam transcriptome library of ICE-L. Then, the nucleotide and predicted amino acid sequences were, respectively, analyzed by various bioinformatics approaches to gain more insights into the computed physicochemical properties of the CaM. Potential involvements of Cam in responding to certain stimuli (i.e., UVB radiation, high salinity, and temperature) were investigated by differential expression, measuring its transcription levels by means of quantitative RT-PCR. Results showed that CaM was indeed inducible and regulated by high UVB radiation, high salinity, and nonoptimal temperature conditions. Different conditions had different expression tendencies, which provided an important basis for investigating the adaptation mechanism of Cam in ICE-L.
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Affiliation(s)
- Ying-Ying He
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China.,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China
| | - Yi-Bin Wang
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China. .,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China. .,Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266235, China.
| | - Zhou Zheng
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China.,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China.,Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266235, China
| | - Fang-Ming Liu
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China.,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China.,Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266235, China
| | - Mei-Ling An
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China.,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China
| | - Xiao-Dong He
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China.,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China
| | - Chang-Feng Qu
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China.,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China
| | - Lu-Lu Li
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China.,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China
| | - Jin-Lai Miao
- The First Institute of Oceanography, State Oceanic Administration, No. 6 of Xianxialing Road, Qingdao, 266061, China. .,Key Laboratory of Marine Bioactive Substances, SOA, Qingdao, 266061, China. .,Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266235, China.
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8
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Harborne SPD, Ruprecht JJ, Kunji ERS. Calcium-induced conformational changes in the regulatory domain of the human mitochondrial ATP-Mg/Pi carrier. BIOCHIMICA ET BIOPHYSICA ACTA 2015; 1847:1245-53. [PMID: 26164100 PMCID: PMC4562336 DOI: 10.1016/j.bbabio.2015.07.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Revised: 06/15/2015] [Accepted: 07/06/2015] [Indexed: 12/21/2022]
Abstract
The mitochondrial ATP-Mg/Pi carrier imports adenine nucleotides from the cytosol into the mitochondrial matrix and exports phosphate. The carrier is regulated by the concentration of cytosolic calcium, altering the size of the adenine nucleotide pool in the mitochondrial matrix in response to energetic demands. The protein consists of three domains; (i) the N-terminal regulatory domain, which is formed of two pairs of fused calcium-binding EF-hands, (ii) the C-terminal mitochondrial carrier domain, which is involved in transport, and (iii) a linker region with an amphipathic α-helix of unknown function. The mechanism by which calcium binding to the regulatory domain modulates substrate transport in the carrier domain has not been resolved. Here, we present two new crystal structures of the regulatory domain of the human isoform 1. Careful analysis by SEC confirmed that although the regulatory domain crystallised as dimers, full-length ATP-Mg/Pi carrier is monomeric. Therefore, the ATP-Mg/Pi carrier must have a different mechanism of calcium regulation than the architecturally related aspartate/glutamate carrier, which is dimeric. The structure showed that an amphipathic α-helix is bound to the regulatory domain in a hydrophobic cleft of EF-hand 3/4. Detailed bioinformatics analyses of different EF-hand states indicate that upon release of calcium, EF-hands close, meaning that the regulatory domain would release the amphipathic α-helix. We propose a mechanism for ATP-Mg/Pi carriers in which the amphipathic α-helix becomes mobile upon release of calcium and could block the transport of substrates across the mitochondrial inner membrane.
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Affiliation(s)
- Steven P D Harborne
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - Jonathan J Ruprecht
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - Edmund R S Kunji
- The Medical Research Council, Mitochondrial Biology Unit, Cambridge Biomedical Campus, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK.
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9
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Non-immune immunoglobulins shield Schistosoma japonicum from host immunorecognition. Sci Rep 2015; 5:13434. [PMID: 26299686 PMCID: PMC4547136 DOI: 10.1038/srep13434] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 07/27/2015] [Indexed: 11/18/2022] Open
Abstract
Schistosomiasis is a major human parasitic disease with a global impact. Schistosoma japonicum, the most difficult to control, can survive within host veins for decades. Mechanisms of immune evasion by the parasite, including antigenic variation and surface masking, have been implicated but not well defined. In this study, we defined the immunoglobulin-binding proteomes of S. japonicum using human IgG, IgM, and IgE as the molecular bait for affinity purification, followed by protein identification by liquid chromatography with tandem mass spectrometry (LC-MS/MS). Several proteins situated at the tegument of S. japonicum were able to nonselectively bind to the Fc domain of host immunoglobulins, indicating a mechanism for the avoidance of host immune attachment and recognition. The profile of the immunoglobulin-binding proteomes provides further clues for immune evasion mechanisms adopted by S. japonicum.
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10
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Optimized orthogonal translation of unnatural amino acids enables spontaneous protein double-labelling and FRET. Nat Chem 2014; 6:393-403. [PMID: 24755590 DOI: 10.1038/nchem.1919] [Citation(s) in RCA: 203] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Accepted: 03/12/2014] [Indexed: 12/13/2022]
Abstract
The ability to introduce different biophysical probes into defined positions in target proteins will provide powerful approaches for interrogating protein structure, function and dynamics. However, methods for site-specifically incorporating multiple distinct unnatural amino acids are hampered by their low efficiency. Here we provide a general solution to this challenge by developing an optimized orthogonal translation system that uses amber and evolved quadruplet-decoding transfer RNAs to encode numerous pairs of distinct unnatural amino acids into a single protein expressed in Escherichia coli with a substantial increase in efficiency over previous methods. We also provide a general strategy for labelling pairs of encoded unnatural amino acids with different probes via rapid and spontaneous reactions under physiological conditions. We demonstrate the utility of our approach by genetically directing the labelling of several pairs of sites in calmodulin with fluorophores and probing protein structure and dynamics by Förster resonance energy transfer.
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11
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Yang Q, Brüschweiler S, Chou JJ. A self-sequestered calmodulin-like Ca²⁺ sensor of mitochondrial SCaMC carrier and its implication to Ca²⁺-dependent ATP-Mg/P(i) transport. Structure 2013; 22:209-17. [PMID: 24332718 DOI: 10.1016/j.str.2013.10.018] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Revised: 10/11/2013] [Accepted: 10/29/2013] [Indexed: 10/25/2022]
Abstract
The mitochondrial carriers play essential roles in energy metabolism. The short Ca²⁺-binding mitochondrial carrier (SCaMC) transports ATP-Mg in exchange for Pi and is important for activities that depend on adenine nucleotides. SCaMC adopts, in addition to the transmembrane domain (TMD) that transports solutes, an extramembrane N-terminal domain (NTD) that regulates solute transport in a Ca²⁺-dependent manner. Crystal structure of the Ca²⁺-bound NTD reveals a compact architecture in which the functional EF hands are sequestered by an endogenous helical segment. Nuclear magnetic resonance (NMR) relaxation rates indicated that removal of Ca²⁺ from NTD results in a major conformational switch from the rigid and compact Ca²⁺-bound state to the dynamic and loose apo state. Finally, we showed using surface plasmon resonance and NMR titration experiments that free apo NTDs could specifically interact with liposome-incorporated TMD, but that Ca²⁺ binding drastically weakened the interaction. Our results together provide a molecular explanation for Ca²⁺-dependent ATP-Mg flux in mitochondria.
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Affiliation(s)
- Qin Yang
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Sven Brüschweiler
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - James J Chou
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
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12
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Bae SH, Dyson HJ, Wright PE. Prediction of the rotational tumbling time for proteins with disordered segments. J Am Chem Soc 2009; 131:6814-21. [PMID: 19391622 DOI: 10.1021/ja809687r] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
For well-structured, rigid proteins, the prediction of rotational tumbling time (tau(c)) using atomic coordinates is reasonably accurate, but is inaccurate for proteins with long unstructured sequences. Under physiological conditions, many proteins contain long disordered segments that play important regulatory roles in fundamental biological events including signal transduction and molecular recognition. Here we describe an ensemble approach to the boundary element method that accurately predicts tau(c) for such proteins by introducing two layers of molecular surfaces whose correlated velocities decay exponentially with distance. Reliable prediction of tau(c) will help to detect intra- and intermolecular interactions and conformational switches between more ordered and less ordered states of the disordered segments. The method has been extensively validated using 12 reference proteins with 14 to 103 disordered residues at the N- and/or C-terminus and has been successfully employed to explain a set of published results on a system that incorporates a conformational switch.
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Affiliation(s)
- Sung-Hun Bae
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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13
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Chen K, Ruan J, Kurgan LA. Prediction of three dimensional structure of calmodulin. Protein J 2006; 25:57-70. [PMID: 16721661 DOI: 10.1007/s10930-006-0011-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2005] [Indexed: 10/24/2022]
Abstract
Calmodulin (CaM) is an important human protein, which has multiple structures. Numerous researchers studied the CaM structures in the past, and about 50 different structures in complex with fragments derived from CaM-regulated proteins have been discovered. Discovery and analysis of existing and new CaM structures is difficult due to the inherent complexity, i.e. flexibility of 6 loops and a central linker that constitute part of the CaM structure. The extensive interest in CaM structure analysis and discovery calls for a comprehensive study, which based on the accumulated expertise would design a method for prediction and analysis of future and existing CaM structures. It is also important to find the mechanisms by which the protein adjusts its structure with respect to various factors. To this end, this paper analyzes the known CaM structures and finds four factors that influence CaM structure, which include existence of Ca2+ binding, different binding segments, measuring surroundings, and sequence mutation. The degree of influence of specific factors on different structural regions is also investigated. Based on the analysis of the relation between the four factors and the corresponding CaM structure a novel method for prediction of the CaM structure in complex with novel segments, given that the surroundings of the complex, is developed. The developed prediction method is tested on a set aside, newest CaM structure. The prediction results provide useful and accurate information about the structure verifying high quality of the proposed prediction method and performed structural analysis.
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Affiliation(s)
- Ke Chen
- College of Mathematical Sciences and LPMC, Chern Institute of Mathematics and Liuhui Center for Applied Mathematics, Nankai University, Tianjin, 300071, Peoples Republic of China
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14
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Project E, Friedman R, Nachliel E, Gutman M. A molecular dynamics study of the effect of Ca2+ removal on calmodulin structure. Biophys J 2006; 90:3842-50. [PMID: 16533845 PMCID: PMC1459500 DOI: 10.1529/biophysj.105.077792] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Calmodulin is a small (148 residues), ubiquitous, highly-conserved Ca(2+) binding protein serving as a modulator of many calcium-dependent processes. In this study, we followed, by means of molecular dynamics, the structural stability of the protein when one of its four bound Ca(2+) ions is removed, and compared it to a simulation of the fully Ca(2+) bound protein. We found that the removal of a single Ca(2+) ion from the N-lobe of the protein, which has a lower affinity for the ion, is sufficient to initiate a considerable structural rearrangement. Although the overall structure of the fully 4 Ca(2+) bound protein remained intact in the extended conformation, the Ca(2+)-removed protein changed its conformation into a compact state. The observation that the 3 Ca(2+) loaded protein assumes a compacted solution state is in accord with experimental observation that the NSCP protein, which binds only three Ca(2+) ions, is natively in a compact state. Examination of the folding dynamics reveals a cooperation between the C-lobe, N-lobe, and the interdomain helix that enable the conformation change. The forces driving this conformational change are discussed.
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Affiliation(s)
- Elad Project
- Laser Laboratory for Fast Reactions in Biology Biochemistry, Tel Aviv University, 69978 Tel Aviv, Israel
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15
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Likic VA, Gooley PR, Speed TP, Strehler EE. A statistical approach to the interpretation of molecular dynamics simulations of calmodulin equilibrium dynamics. Protein Sci 2006; 14:2955-63. [PMID: 16322577 PMCID: PMC2253239 DOI: 10.1110/ps.051681605] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
A sample of 35 independent molecular dynamics (MD) simulations of calmodulin (CaM) equilibrium dynamics was prepared from different but equally plausible initial conditions (20 simulations of the wild-type protein and 15 simulations of the D129N mutant). CaM's radius of gyration and backbone mean-square fluctuations were analyzed for the effect of the D129N mutation, and simulations were compared with experiments. Statistical tests were employed for quantitative comparisons at the desired error level. The computational model predicted statistically significant compaction of CaM relative to the crystal structure, consistent with the results of small-angle X-ray scattering (SAXS) experiments. This effect was not observed in several previously reported studies of (Ca2+)(4)-CaM, which relied on a single MD run. In contrast to radius of gyration, backbone mean-square fluctuations showed a distinctly non-normal and positively skewed distribution for nearly all residues. Furthermore, the D129N mutation affected the backbone dynamics in a complex manner and reduced the mobility of Glu123, Met124, Ile125, Arg126, and Glu127 located in the adjacent alpha-helix G. The implications of these observations for the comparisons of MD simulations with experiments are discussed. The proposed approach may be useful in studies of protein equilibrium dynamics where MD simulations fall short of properly sampling the conformational space, and when the comparison with experiments is affected by the reproducibility of the computational model.
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Affiliation(s)
- Vladimir A Likic
- Reprints requests to: Dr Vladimir A. Likić, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, VIC 3052, Australia.
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16
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Chyan CL, Huang PC, Lin TH, Huang JW, Lin SS, Huang HB, Chen YC. Purification, crystallization and preliminary crystallographic studies of a calmodulin-OLFp hybrid molecule. Acta Crystallogr Sect F Struct Biol Cryst Commun 2005; 61:785-7. [PMID: 16511158 PMCID: PMC1952352 DOI: 10.1107/s1744309105023006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2005] [Accepted: 07/19/2005] [Indexed: 11/10/2022]
Abstract
A hybrid molecule consisting of calmodulin (CaM) and the CaM-binding domain of olfactory nucleotide-gated ion-channel peptide (CaM-OLFp) was purified and crystallized by the hanging-drop vapour-diffusion method at 298 K. The crystals diffracted to a maximum resolution of 1.85 A at cryogenic temperature (100 K) using X-rays from a rotating anode (Cu, wavelength 1.54 A). The crystal belongs to the monoclinic space group C2, with unit-cell parameters a = 64.76, b = 36.23, c = 70.96 A, alpha = gamma = 90, beta = 109.4 degrees. Analysis of the packing density shows that the asymmetric unit contains one CaM-OLFp hybrid molecule with a solvent content of 36.42%.
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Affiliation(s)
- Chia-Lin Chyan
- Department of Chemistry, National Dong-Hwa University, Hualien 974, Taiwan
- Correspondence e-mail: ,
| | - Po-Chung Huang
- Department of Chemistry, National Dong-Hwa University, Hualien 974, Taiwan
| | - Ta-Hsien Lin
- Department of Medical Research and Education, Veterans General Hospital Taipei, Shihpai, Taipei 112, Taiwan
- Institute of Biochemistry, Structural Biology Program, National Yang-Ming University, Shihpai, Taipei 112, Taiwan
| | - Jian-Wen Huang
- Department of Chemistry, National Dong-Hwa University, Hualien 974, Taiwan
| | - S. S. Lin
- Institute of Biochemistry, Structural Biology Program, National Yang-Ming University, Shihpai, Taipei 112, Taiwan
| | - Hsien-bin Huang
- Institute of Molecular Biology, National Chung-Cheng University, Chiayi 520, Taiwan
| | - Yi-Cheng Chen
- Department of Medical Research and Education, Veterans General Hospital Taipei, Shihpai, Taipei 112, Taiwan
- Department of Medical Technology, Tzu Chi University, Hualien 970, Taiwan
- Correspondence e-mail: ,
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17
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Turjanski AG, Estrin DA, Rosenstein RE, McCormick JE, Martin SR, Pastore A, Biekofsky RR, Martorana V. NMR and molecular dynamics studies of the interaction of melatonin with calmodulin. Protein Sci 2005; 13:2925-38. [PMID: 15498938 PMCID: PMC2286588 DOI: 10.1110/ps.04611404] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Pineal hormone melatonin (N-acetyl-5-methoxytryptamine) is thought to modulate the calcium/calmodulin signaling pathway either by changing intracellular Ca(2+) concentration via activation of its G-protein-coupled membrane receptors, or through a direct interaction with calmodulin (CaM). The present work studies the direct interaction of melatonin with intact calcium-saturated CaM both experimentally, by fluorescence and nuclear magnetic resonance spectroscopies, and theoretically, by molecular dynamics simulations. The analysis of the experimental data shows that the interaction is calcium-dependent. The affinity, as obtained from monitoring (15)N and (1)H chemical shift changes for a melatonin titration, is weak (in the millimolar range) and comparable for the N- and C-terminal domains. Partial replacement of diamagnetic Ca(2+) by paramagnetic Tb(3+) allowed the measurement of interdomain NMR pseudocontact shifts and residual dipolar couplings, indicating that each domain movement in the complex is not correlated with the other one. Molecular dynamics simulations allow us to follow the dynamics of melatonin in the binding pocket of CaM. Overall, this study provides an example of how a combination of experimental and theoretical approaches can shed light on a weakly interacting system of biological and pharmacological significance.
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Affiliation(s)
- Adrián G Turjanski
- Departamento de Química Inorgánica, Analítica y Química-Física, INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina
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18
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Wang B, Martin SR, Newman RA, Hamilton SL, Shea MA, Bayley PM, Beckingham KM. Biochemical properties of V91G calmodulin: A calmodulin point mutation that deregulates muscle contraction in Drosophila. Protein Sci 2005; 13:3285-97. [PMID: 15557269 PMCID: PMC2287309 DOI: 10.1110/ps.04928204] [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: 10/26/2022]
Abstract
A mutation (Cam7) to the single endogenous calmodulin gene of Drosophila generates a mutant protein with valine 91 changed to glycine (V91G D-CaM). This mutation produces a unique pupal lethal phenotype distinct from that of a null mutation. Genetic studies indicate that the phenotype reflects deregulation of calcium fluxes within the larval muscles, leading to hypercontraction followed by muscle failure. We investigated the biochemical properties of V91G D-CaM. The effects of the mutation on free CaM are minor: Calcium binding, and overall secondary and tertiary structure are indistinguishable from those of wild type. A slight destabilization of the C-terminal domain is detectable in the calcium-free (apo-) form, and the calcium-bound (holo-) form has a somewhat lower surface hydrophobicity. These findings reinforce the indications from the in vivo work that interaction with a specific CaM target(s) underlies the mutant defects. In particular, defective regulation of ryanodine receptor (RyR) channels was indicated by genetic interaction analysis. Studies described here establish that the putative CaM binding region of the Drosophila RyR (D-RyR) binds wild-type D-CaM comparably to the equivalent CaM-RyR interactions seen for the mammalian skeletal muscle RyR channel isoform (RYR1). The V91G mutation weakens the interaction of both apo- and holo-D-CaM with this binding region, and decreases the enhancement of the calcium-binding affinity of CaM that is detectable in the presence of the RyR target peptide. The predicted functional consequences of these changes are consonant with the in vivo phenotype, and indicate that D-RyR is one, if not the major, target affected by the V91G mutation in CaM.
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Affiliation(s)
- Bo Wang
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251, USA
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19
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Casey DM, Inaba K, Pazour GJ, Takada S, Wakabayashi KI, Wilkerson CG, Kamiya R, Witman GB. DC3, the 21-kDa subunit of the outer dynein arm-docking complex (ODA-DC), is a novel EF-hand protein important for assembly of both the outer arm and the ODA-DC. Mol Biol Cell 2003; 14:3650-63. [PMID: 12972554 PMCID: PMC196557 DOI: 10.1091/mbc.e03-01-0057] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The outer dynein arm-docking complex (ODA-DC) is a microtubule-associated structure that targets the outer dynein arm to its binding site on the flagellar axoneme (Takada et al. 2002. Mol. Biol. Cell 13, 1015-1029). The ODA-DC of Chlamydomonas contains three proteins, referred to as DC1, DC2, and DC3. We here report the isolation and sequencing of genomic and full-length cDNA clones encoding DC3. The sequence predicts a 21,341 Da protein with four EF-hands that is a member of the CTER (calmodulin, troponin C, essential and regulatory myosin light chains) group and is most closely related to a predicted protein from Plasmodium. The DC3 gene, termed ODA14, is intronless. Chlamydomonas mutants that lack DC3 exhibit slow, jerky swimming because of loss of some but not all outer dynein arms. Some outer doublet microtubules without arms had a "partial" docking complex, indicating that DC1 and DC2 can assemble in the absence of DC3. In contrast, DC3 cannot assemble in the absence of DC1 or DC2. Transformation of a DC3-deletion strain with the wild-type DC3 gene rescued both the motility phenotype and the structural defect, whereas a mutated DC3 gene was incompetent to rescue. The results indicate that DC3 is important for both outer arm and ODA-DC assembly.
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Affiliation(s)
- Diane M Casey
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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20
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VanScyoc WS, Shea MA. Phenylalanine fluorescence studies of calcium binding to N-domain fragments of Paramecium calmodulin mutants show increased calcium affinity correlates with increased disorder. Protein Sci 2001; 10:1758-68. [PMID: 11514666 PMCID: PMC2253193 DOI: 10.1110/ps.11601] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2001] [Revised: 05/22/2001] [Accepted: 05/30/2001] [Indexed: 10/16/2022]
Abstract
Calmodulin (CaM) is a ubiquitous, essential calcium-binding protein that regulates diverse protein targets in response to physiological calcium fluctuations. Most high-resolution structures of CaM-target complexes indicate that the two homologous domains of CaM are equivalent partners in target recognition. However, mutations between calcium-binding sites I and II in the N-domain of Paramecium calmodulin (PCaM) selectively affect calcium-dependent sodium currents. To understand these domain-specific effects, N-domain fragments (PCaM(1-75)) of six of these mutants were examined to determine whether energetics of calcium binding to sites I and II or conformational properties had been perturbed. These PCaM((1-75)) sequences naturally contain 5 Phe residues but no Tyr or Trp; calcium binding was monitored by observing the reduction in intrinsic phenylalanine fluorescence at 280 nm. To assess mutation-induced conformational changes, thermal denaturation of the apo PCaM((1-75)) sequences, and calcium-dependent changes in Stokes radii were determined. The free energy of calcium binding to each mutant was within 1 kcal/mole of the value for wild type and calcium reduced the R(s) of all of them. A striking trend was observed whereby mutants showing an increase in calcium affinity and R(s) had a concomitant decrease in thermal stability (by as much as 18 degrees C). Thus, mutations between the binding sites that increased disorder and reduced tertiary constraints in the apo state promoted calcium coordination. This finding underscores the complexity of the linkage between calcium binding and conformational change and the difficulty in predicting mutational effects.
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Affiliation(s)
- W S VanScyoc
- Department of Biochemistry, University of Iowa College of Medicine, Iowa City, Iowa 52242-1109, USA
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21
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Yamashita RA, Sellers JR, Anderson JB. Identification and analysis of the myosin superfamily in Drosophila: a database approach. J Muscle Res Cell Motil 2001; 21:491-505. [PMID: 11206129 DOI: 10.1023/a:1026589626422] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The recent sequencing of the genome of Drosophila melanogaster has provided a valuable resource for mining the database for genes of interest. We took advantage of this opportunity in an attempt to identify novel myosins in Drosophila and confirm the presence of the previously identified myosins from classes I, II, III, V, VI, and VII. The Drosophila database annotators predicted the structure of three additional proteins which we identified as novel unconventional myosins, two of which fell into classes XV and XVIII, respectively. Our own efforts predicted the presence of four additional partial sequences that appear to be myosin proteins which did not fall into any specific class. In the future comparative genomics will hopefully lead to the placement of these myosins into new classes.
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Affiliation(s)
- R A Yamashita
- Laboratory of Molecular Cardiology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA
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22
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Hazard AL, Kohout SC, Stricker NL, Putkey JA, Falke JJ. The kinetic cycle of cardiac troponin C: calcium binding and dissociation at site II trigger slow conformational rearrangements. Protein Sci 1998; 7:2451-9. [PMID: 9828012 PMCID: PMC2143865 DOI: 10.1002/pro.5560071123] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The goal of this study is to characterize the kinetic mechanism of Ca2+ activation and inactivation of cardiac troponin C (cTnC), the Ca2+ signaling protein which triggers heart muscle contraction. Previous studies have shown that IAANS covalently coupled to Cys84 of wild-type cTnC is sensitive to conformational change caused by Ca2+ binding to the regulatory site II; the present study also utilizes the C35S mutant, in which Cys84 is the lone cysteine, to ensure the specificity of IAANS labeling. Site II Ca2+ affinities for cTnC-wt, cTnC-C35S, cTnC-wt-IAANS2, and cTnC-C35S-IAANS were similar (KD = 2-5 microM at 25 degrees C; KD = 2-8 microM at 4 degrees C), indicating that neither the IAANS label nor the C35S mutation strongly perturbs site II Ca2+ affinity. To directly determine the rate of Ca2+ dissociation from site II, the Ca2+-loaded protein was rapidly mixed with a spectroscopically sensitive chelator in a stopped flow spectrometer. The resulting site II Ca2+ off-rates were k(off) = 700-800 s(-1) (4 degrees C) for both cTnC-wt and cTnC-C35S, yielding calculated macroscopic site II Ca2+ on-rates of k(on) = k(off)/KD = 2-4 x 10(8) M(-1) s(-1) (4 degrees C). As observed for Ca2+ affinities, neither the C35S mutation nor IAANS labeling significantly altered the Ca2+ on- and off-rates. Using IAANS fluorescence as a monitor of the protein conformational state, the intramolecular conformational changes (delta) induced by Ca2+ binding and release at site II were found to be significantly slower than the Ca2+ on- and off-rates. The conformational rate constants measured for cTnC-wt-IAANS2 and cTnC-C35S-IAANS were k(delta on) = 120-210 s(-1) and k(delta off) = 90-260 s(-1) (4 degrees C) . Both conformational events were slowed in cTnC-wt-IAANS2 relative to cTnC-C35S-IAANS, presumably due to the bulky IAANS probe coupled to Cys35. Together, the results provide a nearly complete kinetic description of the Ca2+ activation cycle of isolated cTnC, revealing rapid Ca2+ binding and release at site II accompanied by slow conformational steps that are likely to be retained by the full troponin complex during heart muscle contraction and relaxation.
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Affiliation(s)
- A L Hazard
- Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309-0215, USA
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23
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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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24
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Peersen OB, Madsen TS, Falke JJ. Intermolecular tuning of calmodulin by target peptides and proteins: differential effects on Ca2+ binding and implications for kinase activation. Protein Sci 1997; 6:794-807. [PMID: 9098889 PMCID: PMC2144748 DOI: 10.1002/pro.5560060406] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Ca(2+)-activated calmodulin (CaM) regulates many target enzymes by docking to an amphiphilic target helix of variable sequence. This study compares the equilibrium Ca2+ binding and Ca2+ dissociation kinetics of CaM complexed to target peptides derived from five different CaM-regulated proteins: phosphorylase kinase. CaM-dependent protein kinase II, skeletal and smooth myosin light chain kinases, and the plasma membrane Ca(2+)-ATPase. The results reveal that different target peptides can tune the Ca2+ binding affinities and kinetics of the two CaM domains over a wide range of Ca2+ concentrations and time scales. The five peptides increase the Ca2+ affinity of the N-terminal regulatory domain from 14- to 350-fold and slow its Ca2+ dissociation kinetics from 60- to 140-fold. Smaller effects are observed for the C-terminal domain, where peptides increase the apparent Ca2+ affinity 8- to 100-fold and slow dissociation kinetics 13- to 132-fold. In full-length skeletal myosin light chain kinase the inter-molecular tuning provided by the isolated target peptide is further modulated by other tuning interactions, resulting in a CaM-protein complex that has a 10-fold lower Ca2+ affinity than the analogous CaM-peptide complex. Unlike the CaM-peptide complexes, Ca2+ dissociation from the protein complex follows monoexponential kinetics in which all four Ca2+ ions dissociate at a rate comparable to the slow rate observed in the peptide complex. The two Ca2+ ions bound to the CaM N-terminal domain are substantially occluded in the CaM-protein complex. Overall, the results indicate that the cellular activation of myosin light chain kinase is likely to be triggered by the binding of free Ca2(2+)-CaM or Ca4(2+)-CaM after a Ca2+ signal has begun and that inactivation of the complex is initiated by a single rate-limiting event, which is proposed to be either the direct dissociation of Ca2+ ions from the bound C-terminal domain or the dissociation of Ca2+ loaded C-terminal domain from skMLCK. The observed target-induced variations in Ca2+ affinities and dissociation rates could serve to tune CaM activation and inactivation for different cellular pathways, and also must counterbalance the variable energetic costs of driving the activating conformational change in different target enzymes.
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Affiliation(s)
- O B Peersen
- Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309-0215, USA
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25
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Sorensen BR, Shea MA. Calcium binding decreases the stokes radius of calmodulin and mutants R74A, R90A, and R90G. Biophys J 1996; 71:3407-20. [PMID: 8968610 PMCID: PMC1233828 DOI: 10.1016/s0006-3495(96)79535-8] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Calmodulin (CaM) is an intracellular cooperative calcium-binding protein essential for activating many diverse target proteins. Biophysical studies of the calcium-induced conformational changes of CaM disagree on the structure of the linker between domains and possible orientations of the domains. Molecular dynamics studies have predicted that Ca4(2+)CaM is in equilibrium between an extended and compact conformation and that Arg74 and Arg90 are critical to the compaction process. In this study gel permeation chromatography was used to resolve calcium-induced changes in the hydrated shape of CaM at pH 7.4 and 5.6. Results showed that mutation of Arg 74 to Ala increases the R(s) as predicted; however, the average separation of domains in Ca4(2+)-CaM was larger than predicted by molecular dynamics. Mutation of Arg90 to Ala or Gly affected the dimensions of apo-CaM more than those of Ca4(2+)-CaM. Calcium binding to CaM and mutants (R74A-CaM, R90A-CaM, and R90G-CaM) lowered the Stokes radius (R(s)). Differences between R(s) values reported here and Rg values determined by small-angle x-ray scattering studies illustrate the importance of using multiple techniques to explore the solution properties of a flexible protein such as CaM.
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Affiliation(s)
- B R Sorensen
- Department of Biochemistry, University of Iowa College of Medicine, Iowa City 52242-1109, USA
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26
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Bayley PM, Findlay WA, Martin SR. Target recognition by calmodulin: dissecting the kinetics and affinity of interaction using short peptide sequences. Protein Sci 1996; 5:1215-28. [PMID: 8819155 PMCID: PMC2143466 DOI: 10.1002/pro.5560050701] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The interaction between calmodulin (CaM) and peptide M13, its target binding sequence from skeletal muscle myosin light chain kinase, involves predominantly two sets of interactions, between the N-terminal target residues and the C-domain of calmodulin, and between the C-terminal target residues and the N-domain of calmodulin (Ikura M et al., 1992, Science 256:632-638). Using short synthetic peptides based on the two halves of the target sequence, the interactions with calmodulin and its separate C-domain have been studied by fluorescence and CD spectroscopy, calcium binding, and kinetic techniques. Peptide WF10 (residues 1-10 of M13) binds to CaM with Kd approximately 1 microM; peptide FW10 (residues 9-18 of M13, with Phe-17-->Trp substitution) binds to CaM with Kd approximately 100 microM. The effect of peptide WF10 on calcium binding to calmodulin produces a biphasic saturation curve, with marked enhancement of affinity for the binding of two calcium ions to the C-domain, forming a stable half-saturated complex, Ca2-CaM-peptide, and confirming the functional importance of the interaction of this sequence with the C-domain. Stopped-flow studies show that the EGTA-induced dissociation of WF10 from Ca4-CaM proceeds by a reversible relaxation mechanism from a kinetic intermediate state, also involving half-saturation of CaM, and the same mechanism is evident for the full target peptide. Interaction of the N-terminal target residues with the C-domain is energetically the most important component, but interaction of calmodulin with the whole target sequence is necessary to induce the full cooperative interaction of the two contiguous elements of the target sequence with both N- and C-domains of calmodulin. Thus, the interaction of calmodulin with the M13 sequence can be dissected on both a structural and kinetic basis into partial reactions involving intermediates comprising distinct regions of the target sequence. We propose a general mechanism for the calcium regulation of calmodulin-dependent enzyme activation, involving an intermediate complex formed by interaction of the calmodulin C-domain and the corresponding part of the target sequence. This intermediate species can function to regulate the overall calcium sensitivity of activation and to determine the affinity of the calmodulin target interaction.
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Affiliation(s)
- P M Bayley
- Division of Physical Biochemistry, National Institute for Medical Research, Mill Hill, London, United Kingdom.
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27
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Mukherjea P, Maune JF, Beckingham K. Interlobe communication in multiple calcium-binding site mutants of Drosophila calmodulin. Protein Sci 1996; 5:468-77. [PMID: 8868483 PMCID: PMC2143358 DOI: 10.1002/pro.5560050308] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We have generated mutants of Drosophila calmodulin in which pairs of calcium-binding sites are mutated so as to prevent calcium binding. In all sites, the mutation involves replacement of the -Z position glutamate residue with glutamine. Mutants inactivated in both N-terminal sites (B12Q) or both C-terminal sites (B34Q), and two mutants with one N- and one C-terminal site inactivated (B13Q and B24Q) were generated. The quadruple mutant with all four sites mutated was also studied. UV-difference spectroscopy and near-UV CD were used to examine the influence of these mutations upon the single tyrosine (Tyr-138) of the protein. These studies uncovered four situations in which Tyr-138 in the C-terminal lobe responds to a change to the calcium-binding properties of the N-terminal lobe. Further, they suggest that N-terminal calcium-binding events contribute strongly to the aberrant behavior of Tyr-138 seen in mutants with a single functional C-terminal calcium-binding site. The data also indicate that loss of calcium binding at site 1 adjusts the aberrant conformation of Tyr-138 produced by mutation of site 3 toward the wild-type structure. However, activation studies for skeletal muscle myosin light chain kinase (SK-MLCK) established that all of the multiple binding site mutants are poor activators of SK-MLCK. Thus, globally, the calcium-induced conformation of B13Q is not closer to wild type than that of either the site 1 or the site 3 mutant. The positioning of Tyr-138 within the crystal structure of calmodulin suggests that effects of the N-terminal lobe on this residue may be mediated via changes to the central linker region of the protein.
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Affiliation(s)
- P Mukherjea
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA
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28
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Howarth JW, Krudy GA, Lin X, Putkey JA, Rosevear PR. An NMR and spin label study of the effects of binding calcium and troponin I inhibitory peptide to cardiac troponin C. Protein Sci 1995; 4:671-80. [PMID: 7613465 PMCID: PMC2143097 DOI: 10.1002/pro.5560040407] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The paramagnetic relaxation reagent, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy (HyTEMPO), was used to probe the surface exposure of methionine residues of recombinant cardiac troponin C (cTnC) in the absence and presence of Ca2+ at the regulatory site (site II), as well as in the presence of the troponin I inhibitory peptide (cTnIp). Methyl resonances of the 10 Met residues of cTnC were chosen as spectral probes because they are thought to play a role in both formation of the N-terminal hydrophobic pocket and in the binding of cTnIp. Proton longitudinal relaxation rates (R1's) of the [13C-methyl] groups in [13C-methyl]Met-labeled cTnC(C35S) were determined using a T1 two-dimensional heteronuclear single- and multiple-quantum coherence pulse sequence. Solvent-exposed Met residues exhibit increased relaxation rates from the paramagnetic effect of HyTEMPO. Relaxation rates in 2Ca(2+)-loaded and Ca(2+)-saturated cTnC, both in the presence and absence of HyTEMPO, permitted the topological mapping of the conformational changes induced by the binding of Ca2+ to site II, the site responsible for triggering muscle contraction. Calcium binding at site II resulted in an increased exposure of Met residues 45 and 81 to the soluble spin label HyTEMPO. This result is consistent with an opening of the hydrophobic pocket in the N-terminal domain of cTnC upon binding Ca2+ at site II. The binding of the inhibitory peptide cTnIp, corresponding to Asn 129 through Ile 149 of cTnI, to both 2Ca(2+)-loaded and Ca(2+)-saturated cTnC was shown to protect Met residues 120 and 157 from HyTEMPO as determined by a decrease in their measured R1 values. These results suggest that in both the 2Ca(2+)-loaded and Ca(2+)-saturated forms of cTnC, cTnIp binds primarily to the C-terminal domain of cTnC.
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Affiliation(s)
- J W Howarth
- Department of Biochemistry and Molecular Biology, University of Texas Medical School-Houston 77225, USA
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Borders CL, Broadwater JA, Bekeny PA, Salmon JE, Lee AS, Eldridge AM, Pett VB. A structural role for arginine in proteins: multiple hydrogen bonds to backbone carbonyl oxygens. Protein Sci 1994; 3:541-8. [PMID: 8003972 PMCID: PMC2142871 DOI: 10.1002/pro.5560030402] [Citation(s) in RCA: 145] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We propose that arginine side chains often play a previously unappreciated general structural role in the maintenance of tertiary structure in proteins, wherein the positively charged guanidinium group forms multiple hydrogen bonds to backbone carbonyl oxygens. Using as a criterion for a "structural" arginine one that forms 4 or more hydrogen bonds to 3 or more backbone carbonyl oxygens, we have used molecular graphics to locate arginines of interest in 4 proteins: Arg 180 in Thermus thermophilus manganese superoxide dismutase, Arg 254 in human carbonic anhydrase II, Arg 31 in Streptomyces rubiginosus xylose isomerase, and Arg 313 in Rhodospirillum rubrum ribulose-1,5-bisphosphate carboxylase/oxygenase. Arg 180 helps to mold the active site channel of superoxide dismutase, whereas in each of the other enzymes the structural arginine is buried in the "mantle" (i.e., inside, but near the surface) of the protein interior well removed from the active site, where it makes 5 hydrogen bonds to 4 backbone carbonyl oxygens. Using a more relaxed criterion of 3 or more hydrogen bonds to 2 or more backbone carbonyl oxygens, arginines that play a potentially important structural role were found in yeast enolase, Bacillus stearothermophilus glyceraldehyde-3-phosphate dehydrogenase, bacteriophage T4 and human lysozymes, Enteromorpha prolifera plastocyanin, HIV-1 protease, Trypanosoma brucei brucei and yeast triosephosphate isomerases, and Escherichia coli trp aporepressor (but not trp repressor or the trp repressor/operator complex).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- C L Borders
- Department of Chemistry, College of Wooster, Ohio 44691
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Renner M, Danielson MA, Falke JJ. Kinetic control of Ca(II) signaling: tuning the ion dissociation rates of EF-hand Ca(II) binding sites. Proc Natl Acad Sci U S A 1993; 90:6493-7. [PMID: 8341660 PMCID: PMC46958 DOI: 10.1073/pnas.90.14.6493] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
EF-hand Ca(II) binding sites share a conserved architecture and are prevalent in Ca(II) signaling pathways. The ion binding kinetics of these sites are carefully tuned to provide the physiologically appropriate activation and inactivation time scales. Here we examine kinetic tuning by the side chain at the ninth position of the EF-loop. A model is proposed in which both the size and charge of the side chain contribute to kinetic tuning. To test this model, the ninth loop position of the EF-hand-like site in the Escherichia coli D-galactose binding protein has been engineered and the Tb(III) dissociation kinetics of the resulting sites have been analyzed. Substitutions at this position are observed to generate up to 10(4)-fold changes in Tb(III) dissociation rates, with little effect on Tb(III) affinity. Furthermore, the observed pattern of rate changes confirm the model's predictions; long side chains at the ninth loop position yield slow dissociation kinetics as predicted for a steric block, whereas acidic side chains yield slow dissociation kinetics as expected for an electrostatic barrier.
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Affiliation(s)
- M Renner
- Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309-0215
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31
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Raghunathan S, Chandross RJ, Cheng BP, Persechini A, Sobottka SE, Kretsinger RH. The linker of des-Glu84-calmodulin is bent. Proc Natl Acad Sci U S A 1993; 90:6869-73. [PMID: 8341712 PMCID: PMC47034 DOI: 10.1073/pnas.90.14.6869] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The crystal structure of a mutant calmodulin (CaM) lacking Glu-84 has been refined to R = 0.23 using data measured to 2.9-A resolution. In native CaM the central helix is fully extended, and the molecule is dumbbell shaped. In contrast, the deletion of Glu-84 causes a bend of 95 degrees in the linker region of the central helix at Ile-85. However, EF-hand domains 1 and 2 (lobe 1,2) do not touch lobe 3,4. The length, by alpha-carbon separation, of des-Glu84-CaM is 56 A; that of native CaM is 64 A. The shape of des-Glu84-CaM is similar to that of native CaM, as it is bound to the target peptide of myosin light-chain kinase. This result supports the proposal that the linker region of the central helix of CaM functions as a flexible tether.
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Affiliation(s)
- S Raghunathan
- Department of Biology, University of Virginia, Charlottesville 22901
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Sekharudu CY, Sundaralingam M. A model for the calmodulin-peptide complex based on the troponin C crystal packing and its similarity to the NMR structure of the calmodulin-myosin light chain kinase peptide complex. Protein Sci 1993; 2:620-5. [PMID: 8518733 PMCID: PMC2142370 DOI: 10.1002/pro.5560020412] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In the crystal structure of troponin C, the holo C-domain is bound in a head-to-tail fashion to the A-helix of the apo N-domain of a symmetry-related molecule. Using this interaction, we have proposed a model for the calmodulin-peptide complex. We find that the interaction of the C-domain with the A-helix is similar to that observed in the NMR structure of the calmodulin-myosin light chain kinase (MLCK) peptide complex. This similarity in binding has enabled us to make a precise sequence alignment of the target peptides in the calmodulin-binding cleft and to rationalize the amino acid sequence-dependent binding strengths of various peptides. Our model differs from that proposed by Strynadka and James (Proteins Struct. Funct. Genet. 7, 234-248, 1990) in that the peptides are rotated by 100 degrees in the calmodulin binding cleft.
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Affiliation(s)
- C Y Sekharudu
- Department of Chemistry, Ohio State University, Columbus 43210
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Rao ST, Wu S, Satyshur KA, Ling KY, Kung C, Sundaralingam M. Structure of Paramecium tetraurelia calmodulin at 1.8 A resolution. Protein Sci 1993; 2:436-47. [PMID: 8453381 PMCID: PMC2142389 DOI: 10.1002/pro.5560020316] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The crystal structure of calmodulin (CaM; M(r) 16,700, 148 residues) from the ciliated protozoan Paramecium tetraurelia (PCaM) has been determined and refined using 1.8 A resolution area detector data. The crystals are triclinic, space group P1, a = 29.66, b = 53.79, c = 25.49 A, alpha = 92.84, beta = 97.02, and gamma = 88.54 degrees with one molecule in the unit cell. Crystals of the mammalian CaM (MCaM; Babu et al., 1988) and Drosophila CaM (DCaM; Taylor et al., 1991) also belong to the same space group with very similar cell dimensions. All three CaMs have 148 residues, but there are 17 sequence changes between PCaM and MCaM and 16 changes between PCaM and DCaM. The initial difference in the molecular orientation between the PCaM and MCaM crystals was approximately 7 degrees as determined by the rotation function. The reoriented Paramecium model was extensively refitted using omit maps and refined using XPLOR. The R-value for 11,458 reflections with F > 3 sigma is 0.21, and the model consists of protein atoms for residues 4-147, 4 calcium ions, and 71 solvent molecules. The root mean square (rms) deviations in the bond lengths and bond angles in the model from ideal values are 0.016 A and 3 degrees, respectively. The molecular orientation of the final PCaM model differs from MCaM by only 1.7 degrees. The overall Paramecium CaM structure is very similar to the other calmodulin structures with a seven-turn long central helix connecting the two terminal domains, each containing two Ca-binding EF-hand motifs. The rms deviation in the backbone N, Ca, C, and O atoms between PCaM and MCaM is 0.52 A and between PCaM and DCaM is 0.85 A. The long central helix regions differ, where the B-factors are also high, particularly in PCaM and MCaM. Unlike the MCaM structure, with one kink at D80 in the middle of the linker region, and the DCaM structure, with two kinks at K75 and I85, in our PCaM structure there are no kinks in the helix; the distortion appears to be more gradually distributed over the entire helical region, which is bent with an apparent radius of curvature of 74.5(2) A. The different distortions in the central helical region probably arise from its inherent mobility.
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Affiliation(s)
- S T Rao
- Department of Chemistry & Biotechnology Center, Ohio State University, Columbus 43210
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