51
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Newman RA, Van Scyoc WS, Sorensen BR, Jaren OR, Shea MA. Interdomain cooperativity of calmodulin bound to melittin preferentially increases calcium affinity of sites I and II. Proteins 2008; 71:1792-812. [DOI: 10.1002/prot.21861] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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52
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Theoharis NT, Sorensen BR, Theisen-Toupal J, Shea MA. The neuronal voltage-dependent sodium channel type II IQ motif lowers the calcium affinity of the C-domain of calmodulin. Biochemistry 2007; 47:112-23. [PMID: 18067319 DOI: 10.1021/bi7013129] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Calmodulin (CaM) is the primary calcium sensor in eukaryotes. Calcium binds cooperatively to pairs of EF-hand motifs in each domain (N and C). This allows CaM to regulate cellular processes via calcium-dependent interactions with a variety of proteins, including ion channels. One neuronal target is NaV1.2, voltage-dependent sodium channel type II, to which CaM binds via an IQ motif within the NaV1.2 C-terminal tail (residues 1901-1938) [Mori, M., et al. (2000) Biochemistry 39, 1316-1323]. Here we report on the use of circular dichroism, fluorescein emission, and fluorescence anisotropy to study the interaction between CaM and NaV1.2 at varying calcium concentrations. At 1 mM MgCl2, both full-length CaM (CaM1-148) and a C-domain fragment (CaM76-148) exhibit tight (nanomolar) calcium-independent binding to the NaV1.2 IQ motif, whereas an N-domain fragment of CaM (CaM1-80) binds weakly, regardless of calcium concentration. Equilibrium calcium titrations of CaM at several concentrations of the NaV1.2 IQ peptide showed that the peptide reduced the calcium affinity of the CaM C-domain sites (III and IV) without affecting the N-domain sites (I and II) significantly. This leads us to propose that the CaM C-domain mediates constitutive binding to the NaV1.2 peptide, but that interaction then distorts calcium-binding sites III and IV, thereby reducing their affinity for calcium. This contrasts with the CaM-binding domains of voltage-dependent Ca2+ channels, kinases, and phosphatases, which increase the calcium binding affinity of the C-domain of CaM.
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Affiliation(s)
- Nathaniel T Theoharis
- Department of Biochemistry, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242-1109, USA
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53
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Zhang W, Wang D, Volk E, Bellen HJ, Hiesinger PR, Quiocho FA. V-ATPase V0 sector subunit a1 in neurons is a target of calmodulin. J Biol Chem 2007; 283:294-300. [PMID: 17933871 DOI: 10.1074/jbc.m708058200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The V(0) complex forms the proteolipid pore of a vesicular ATPase that acidifies vesicles. In addition, an independent function in membrane fusion has been suggested in vacuolar fusion in yeast and synaptic vesicle exocytosis in fly neurons. Evidence for a direct role in secretion has also recently been presented in mouse and worm. The molecular mechanisms of how the V(0) components might act or are regulated are largely unknown. Here we report the identification and characterization of a calmodulin-binding site in the large cytosolic N-terminal region of the Drosophila protein V100, the neuron-specific V(0) subunit a1. V100 forms a tight complex with calmodulin in a Ca(2+)-dependent manner. Mutations in the calmodulin-binding site in Drosophila lead to a loss of calmodulin recruitment to synapses. Neuronal expression of a calmodulin-binding deficient V100 uncovers an incomplete rescue at low levels and cellular toxicity at high levels. Our results suggest a vesicular ATPase V(0)-dependent function of calmodulin at synapses.
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Affiliation(s)
- Wei Zhang
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Houston, Texas 77030
| | - Dong Wang
- Department of Physiology and Green Center Division for Systems Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Elzi Volk
- Department of Physiology and Green Center Division for Systems Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Hugo J Bellen
- Departments of Molecular and Human Genetics and Neuroscience and Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030
| | - Peter Robin Hiesinger
- Department of Physiology and Green Center Division for Systems Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390.
| | - Florante A Quiocho
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Houston, Texas 77030.
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54
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Manceva S, Lin T, Pham H, Lewis JH, Goldman YE, Ostap EM. Calcium regulation of calmodulin binding to and dissociation from the myo1c regulatory domain. Biochemistry 2007; 46:11718-26. [PMID: 17910470 PMCID: PMC2566900 DOI: 10.1021/bi700894h] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Myo1c is an unconventional myosin involved in cell signaling and membrane dynamics. Calcium binding to the regulatory-domain-associated calmodulin affects myo1c motor properties, but the kinetic details of this regulation are not fully understood. We performed actin gliding assays, ATPase measurements, fluorescence spectroscopy, and stopped-flow kinetics to determine the biochemical parameters that define the calmodulin-regulatory-domain interaction. We found calcium moderately increases the actin-activated ATPase activity and completely inhibits actin gliding. Addition of exogenous calmodulin in the presence of calcium fully restores the actin gliding rate. A fluorescently labeled calmodulin mutant (N111C) binds to recombinant peptides containing the myo1c IQ motifs at a diffusion-limited rate in the presence and absence of calcium. Measurements of calmodulin dissociation from the IQ motifs in the absence of calcium show that the calmodulin bound to the IQ motif adjacent to the motor domain (IQ1) has the slowest dissociation rate (0.0007 s-1), and the IQ motif adjacent to the tail domain (IQ3) has the fastest dissociation rate (0.5 s-1). When the complex is equilibrated with calcium, calmodulin dissociates most rapidly from IQ1 (60 s-1). However, this increased rate of dissociation is limited by a slow calcium-induced conformational change (3 s-1). Fluorescence anisotropy decay of fluorescently labeled N111C bound to myo1c did not depend appreciably on Ca2+. Our data suggest that the calmodulin bound to the IQ motif adjacent to the motor domain is rapidly exchangeable in the presence of calcium and is responsible for regulation of myo1c ATPase and motile activity.
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Affiliation(s)
| | | | | | | | | | - E. Michael Ostap
- *Corresponding author: E. Michael Ostap, Department of Physiology, University of Pennsylvania School of Medicine, B400 Richards Building, Philadelphia, PA 19104-6085, Phone: 215-573-9758, Fax: 215-573-1171,
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55
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Williams RJ. The physics and chemistry of the calcium-binding proteins. CIBA FOUNDATION SYMPOSIUM 2007; 122:145-61. [PMID: 3792135 DOI: 10.1002/9780470513347.ch9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The structures of several calcium-binding proteins are known in considerable detail in both crystalline and solution states. The changes of structure with the binding of calcium, protons, magnesium and hydrophobic molecules are also known. It appears that some calcium-binding structures contain relays of cooperative interaction which run via helices between different parts of these proteins, for example in calmodulin. In others the effect of binding, of for instance calcium, is minimal, as in phospholipase A2. In another group the effect of binding of ions leads to cooperative further binding so that ternary or higher-order complexes are formed, as in the activation of prothrombin. The linking of cellular activities to calcium is thus dependent on several highly developed properties of particular proteins in special environments which have been selected to take advantage of the peculiarities of the calcium ion, namely its particular coordination chemistry and its speed of reaction. The link between calcium, its proteins and activity is not directly to catalysis but is primarily to mechanical properties.
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56
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Juranić N, Atanasova E, Streiff JH, Macura S, Prendergast FG. Solvent-induced differentiation of protein backbone hydrogen bonds in calmodulin. Protein Sci 2007; 16:1329-37. [PMID: 17567747 PMCID: PMC2206704 DOI: 10.1110/ps.062689807] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2006] [Revised: 02/18/2007] [Accepted: 02/23/2007] [Indexed: 10/23/2022]
Abstract
In apo and holoCaM, almost half of the hydrogen bonds (H-bonds) at the protein backbone expected from the corresponding NMR or X-ray structures were not detected by h3JNC' couplings. The paucity of the h3JNC' couplings was considered in terms of dynamic features of these structures. We examined a set of seven proteins and found that protein-backbone H-bonds form two groups according to the h3JNC' couplings measured in solution. H-bonds that have h3JNC' couplings above the threshold of 0.2 Hz show distance/angle correlation among the H-bond geometrical parameters, and appear to be supported by the backbone dynamics in solution. The other H-bonds have no such correlation; they populate the water-exposed and flexible regions of proteins, including many of the CaM helices. The observed differentiation in a dynamical behavior of backbone H-bonds in apo and holoCaM appears to be related to protein functions.
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Affiliation(s)
- Nenad Juranić
- Department of Biochemistry and Molecular Biology, Mayo College of Medicine, Mayo Clinic and Foundation, Rochester, MN 55905, USA.
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57
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Yang C, Song H, Wang Y, Peng F, Wei Q. A new approach for producing polyclonal antibodies using impure antigens. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 2007; 70:613-8. [PMID: 17391771 DOI: 10.1016/j.jbbm.2007.02.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2006] [Revised: 01/30/2007] [Accepted: 02/09/2007] [Indexed: 10/23/2022]
Abstract
A new convenient approach has been designed to produce polyclonal antibodies (PcAb). The approach is based on the principle of the immunoglobulin (Ig) class switch in the immune response. We produced six different antibodies (Ab) against calcineurin A subunit (CNA). CNA, His-tagged calcineurin A subunit (His-CNA), single chain calcineurin (CNB-CNA) and single chain calcineurin-calmodulin complex (CaM-CNB-CNA) were expressed in Escherichia coli (E. coli) BL21 strain, and they were used to immunize male BALB/c mice. These Ab were examined by enzyme-linked immunosorbent assay (ELISA) and western blot analysis. The results clearly demonstrated that the specificity of the Ab produced by different protein samples was much higher than that of the Ab produced by a single sample. We used CNA, CaM-CNB-CNA and His-CNA to immunize mice in turn and obtained monospecific PcAb against CNA fortunately by our new approach. Remarkably, our approach not only offered a simple and general alternative to other methods for producing PcAb described previously, but also disclosed a novel process of immunization that could be used to produce monoclonal antibodies (mAb).
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Affiliation(s)
- Chenggang Yang
- Department of Biochemistry and Molecular Biology, Beijing Normal University, Beijing Key Laboratory, Beijing 100875, China
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58
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VanScyoc WS, Newman RA, Sorensen BR, Shea MA. Calcium binding to calmodulin mutants having domain-specific effects on the regulation of ion channels. Biochemistry 2007; 45:14311-24. [PMID: 17128970 DOI: 10.1021/bi061134d] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Calmodulin (CaM) is an essential, eukaryotic protein comprised of two highly homologous domains (N and C). CaM binds four calcium ions cooperatively, regulating a wide array of target proteins. A genetic screen of Paramecia by Kung [Kung, C. et al. (1992) Cell Calcium 13, 413-425] demonstrated that the domains of CaM have separable physiological roles: "under-reactive" mutations affecting calcium-dependent sodium currents mapped to the N-domain, while "over-reactive" mutations affecting calcium-dependent potassium currents localized to the C-domain of CaM. To determine whether and how these mutations affected intrinsic calcium-binding properties of CaM domains, phenylalanine fluorescence was used to monitor calcium binding to sites I and II (N-domain) and tyrosine fluorescence was used to monitor sites III and IV (C-domain). To explore interdomain interactions, binding properties of each full-length mutant were compared to those of its corresponding domain fragments. The calcium-binding properties of six under-reactive mutants (V35I/D50N, G40E, G40E/D50N, D50G, E54K, and G59S) and one over-reactive mutant (M145V) were indistinguishable from those of wild-type CaM, despite their deleterious physiological effects on ion-channel regulation. Four over-reactive mutants (D95G, S101F, E104K, and H135R) significantly decreased the calcium affinity of the C-domain. Of these, one (E104K) also increased the calcium affinity of the N-domain, demonstrating that the magnitude and direction of wild-type interdomain coupling had been perturbed. This suggests that, while some of these mutations alter calcium-binding directly, others probably alter CaM-channel association or calcium-triggered conformational change in the context of a ternary complex with the affected ion channel.
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Affiliation(s)
- Wendy S VanScyoc
- Department of Biochemistry, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242-1109, USA
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59
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Lewis JH, Lin T, Hokanson DE, Ostap EM. Temperature dependence of nucleotide association and kinetic characterization of myo1b. Biochemistry 2006; 45:11589-97. [PMID: 16981718 PMCID: PMC2517419 DOI: 10.1021/bi0611917] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Myo1b is a widely expressed myosin-I isoform that concentrates on endosomal and ruffling membranes and is thought to play roles in membrane trafficking and dynamics. It is one of the best characterized myosin-I isoforms and appears to have unique biochemical properties tuned for tension sensing or tension maintenance. We determined the key biochemical rate constants that define the actomyo1b ATPase cycle at 37 degrees C and measured the temperature dependence of ATP binding, ADP release, and the transition from a nucleotide-inaccessible state to a nucleotide-accessible state (k(alpha)). The rate of ATP binding is highly temperature sensitive, with an Arrhenius activation energy 2-3-fold greater than other characterized myosins (e.g., myosin-II and myosin-V). ATP hydrolysis is fast, and phosphate release is slow and rate limiting with an actin dependence that is nearly identical to the steady-state ATPase parameters (Vmax and K(ATPase)). ADP release is not as temperature dependent as ATP binding. The rates and temperature dependence of ADP release are similar to k(alpha) suggesting that a similar structural change is responsible for both transitions. We calculate a duty ratio of 0.08 based on the biochemical kinetics. However, this duty ratio is likely to be highly sensitive to strain.
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Affiliation(s)
| | | | | | - E. Michael Ostap
- Corresponding author: E. Michael Ostap, Department of Physiology, University of Pennsylvania School of Medicine, B400 Richards Building, Philadelphia, PA 19104-6085, Phone: 215-573-9758, Fax: 215-573-1171,
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60
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Hokanson DE, Laakso JM, Lin T, Sept D, Ostap EM. Myo1c binds phosphoinositides through a putative pleckstrin homology domain. Mol Biol Cell 2006; 17:4856-65. [PMID: 16971510 PMCID: PMC1635404 DOI: 10.1091/mbc.e06-05-0449] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Myo1c is a member of the myosin superfamily that binds phosphatidylinositol-4,5-bisphosphate (PIP(2)), links the actin cytoskeleton to cellular membranes and plays roles in mechano-signal transduction and membrane trafficking. We located and characterized two distinct membrane binding sites within the regulatory and tail domains of this myosin. By sequence, secondary structure, and ab initio computational analyses, we identified a phosphoinositide binding site in the tail to be a putative pleckstrin homology (PH) domain. Point mutations of residues known to be essential for polyphosphoinositide binding in previously characterized PH domains inhibit myo1c binding to PIP(2) in vitro, disrupt in vivo membrane binding, and disrupt cellular localization. The extended sequence of this binding site is conserved within other myosin-I isoforms, suggesting they contain this putative PH domain. We also characterized a previously identified membrane binding site within the IQ motifs in the regulatory domain. This region is not phosphoinositide specific, but it binds anionic phospholipids in a calcium-dependent manner. However, this site is not essential for in vivo membrane binding.
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Affiliation(s)
- David E. Hokanson
- *The Pennsylvania Muscle Institute and Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085; and
| | - Joseph M. Laakso
- *The Pennsylvania Muscle Institute and Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085; and
| | - Tianming Lin
- *The Pennsylvania Muscle Institute and Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085; and
| | - David Sept
- Department of Biomedical Engineering and Center for Computational Biology, Washington University, St. Louis, MO 63130
| | - E. Michael Ostap
- *The Pennsylvania Muscle Institute and Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085; and
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61
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Streiff JH, Allen TW, Atanasova E, Juranic N, Macura S, Penheiter AR, Jones KA. Prediction of volatile anesthetic binding sites in proteins. Biophys J 2006; 91:3405-14. [PMID: 16877516 PMCID: PMC1614498 DOI: 10.1529/biophysj.106.082586] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
Computational methods designed to predict and visualize ligand protein binding interactions were used to characterize volatile anesthetic (VA) binding sites and unoccupied pockets within the known structures of VAs bound to serum albumin, luciferase, and apoferritin. We found that both the number of protein atoms and methyl hydrogen, which are within approximately 8 A of a potential ligand binding site, are significantly greater in protein pockets where VAs bind. This computational approach was applied to structures of calmodulin (CaM), which have not been determined in complex with a VA. It predicted that VAs bind to [Ca(2+)](4)-CaM, but not to apo-CaM, which we confirmed with isothermal titration calorimetry. The VA binding sites predicted for the structures of [Ca(2+)](4)-CaM are located in hydrophobic pockets that form when the Ca(2+) binding sites in CaM are saturated. The binding of VAs to these hydrophobic pockets is supported by evidence that halothane predominantly makes contact with aliphatic resonances in [Ca(2+)](4)-CaM (nuclear Overhauser effect) and increases the Ca(2+) affinity of CaM (fluorescence spectroscopy). Our computational analysis and experiments indicate that binding of VA to proteins is consistent with the hydrophobic effect and the Meyer-Overton rule.
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Affiliation(s)
- John H Streiff
- Departments of Anesthesiology and Molecular Pharmacology and Experimental Therapeutics and Biochemistry and Molecular Biology, Mayo College of Medicine, Rochester, Minnesota, USA.
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62
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Hokanson DE, Ostap EM. Myo1c binds tightly and specifically to phosphatidylinositol 4,5-bisphosphate and inositol 1,4,5-trisphosphate. Proc Natl Acad Sci U S A 2006; 103:3118-23. [PMID: 16492791 PMCID: PMC1413866 DOI: 10.1073/pnas.0505685103] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Myosin-I is the single-headed member of the myosin superfamily that associates with acidic phospholipids through its basic tail domain. Membrane association is essential for proper myosin-I localization and function. However, little is known about the physiological relevance of the direct association of myosin-I with phospholipids or about phospholipid headgroup-binding specificity. To better understand the mechanism of myosin-I-membrane association, we measured effective dissociation constants for the binding of a recombinant myo1c tail construct (which includes three IQ domains and bound calmodulins) to large unilamellar vesicles (LUVs) composed of phosphatidylcholine and various concentrations of phosphatidylserine (PS) or phosphatidylinositol 4,5-bisphosphate (PIP(2)). We found that the myo1c-tail binds tightly to LUVs containing >60% PS but very weakly to LUVs containing physiological PS concentrations (<40%). The myo1c tail and not the IQ motifs bind tightly to LUVs containing 2% PIP(2). Additionally, we found that the myo1c tail binds to soluble inositol-1,4,5-trisphosphate with nearly the same affinity as to PIP(2) in LUVs, suggesting that myo1c binds specifically to the headgroup of PIP(2). We also show that a GFP-myosin-I-tail chimera expressed in epithelial cells is transiently localized to regions known to be enriched in PIP(2). Our results suggest that myo1c does not bind to physiological concentrations of PS but rather binds tightly to PIP(2).
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Affiliation(s)
- David E. Hokanson
- Pennsylvania Muscle Institute and Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
| | - E. Michael Ostap
- Pennsylvania Muscle Institute and Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
- *To whom correspondence should be addressed. E-mail:
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63
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Abstract
Myo1b is a widely expressed myosin-I isoform that concentrates on endosomal and ruffling membranes and is thought to play roles in membrane trafficking and dynamics. Myo1b is alternatively spliced within the regulatory domain of the molecule, yielding isoforms with six (myo1b(a)), five (myo1b(b)), or four (myo1b(c)) non-identical IQ motifs. The calmodulin binding properties of the myo1b IQ motifs have not been investigated, and the mechanical and cell biological consequences of alternative splicing are not known. Therefore, we expressed the alternatively spliced myo1b isoforms truncated after the final IQ motif and included a sequence at their C termini that is a substrate for bacterial biotin ligase. Site-specific biotinylation allows us to specifically attach the myosin to motility surfaces via a biotin-streptavidin linkage. We measured the ATPase and motile properties of the recombinant myo1b splice isoforms, and we correlated these properties with calmodulin binding. We confirmed that calcium-dependent changes in the ATPase activity are due to calcium binding to the calmodulin closest to the motor. We found that calmodulin binds tightly to some of the IQ motifs (Kd < 0.2 microM) and very weakly to the others (Kd > 5 microM), suggesting that a subset of the IQ motifs are not calmodulin bound under physiological conditions. Finally, we found the in vitro motility rate to be dependent on the myo1b isoform and the calmodulin concentration and that the myo1b regulatory domain acts as a rigid lever arm upon calmodulin binding to the high affinity and low affinity IQ motifs.
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Affiliation(s)
- Tianming Lin
- Department of Physiology and The Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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64
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Nalavadi V, Nyitrai M, Bertolini C, Adamek N, Geeves MA, Bähler M. Kinetic mechanism of myosin IXB and the contributions of two class IX-specific regions. J Biol Chem 2005; 280:38957-68. [PMID: 16179355 DOI: 10.1074/jbc.m507161200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Myosin IXb (Myo9b) was reported to be a single-headed, processive myosin. In its head domain it contains an N-terminal extension and a large loop 2 insertion that are specific for class IX myosins. We characterized the kinetic properties of purified, recombinant rat Myo9b, and we compared them with those of Myo9b mutants that had either the N-terminal extension or the loop 2 insertion deleted. Unlike other processive myosins, Myo9b exhibited a low affinity for ADP, and ADP release was not rate-limiting in the ATPase cycle. Myo9b is the first myosin for which ATP hydrolysis or an isomerization step after ATP binding is rate-limiting. Myo9b-ATP appeared to be in a conformation with a weak affinity for actin as determined by pyrene-actin fluorescence. However, in actin cosedimentation experiments, a subpopulation of Myo9b-ATP bound F-actin with a remarkably high affinity. Deletion of the N-terminal extension reduced actin affinity and increased the rate of nucleotide binding. Deletion of the loop 2 insertion reduced the actin affinity and altered the communication between actin and nucleotide-binding sites.
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Affiliation(s)
- Vijayalaxmi Nalavadi
- Institute for General Zoology and Genetics, Westfalian Wilhelms-University, 48149 Münster, Germany
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65
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Contessa GM, Orsale M, Melino S, Torre V, Paci M, Desideri A, Cicero DO. Structure of calmodulin complexed with an olfactory CNG channel fragment and role of the central linker: residual dipolar couplings to evaluate calmodulin binding modes outside the kinase family. JOURNAL OF BIOMOLECULAR NMR 2005; 31:185-199. [PMID: 15803393 DOI: 10.1007/s10858-005-0165-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Accepted: 12/22/2004] [Indexed: 05/24/2023]
Abstract
The NMR high-resolution structure of calmodulin complexed with a fragment of the olfactory cyclic-nucleotide gated channel is described. This structure shows features that are unique for this complex, including an active role of the linker connecting the N- and C-lobes of calmodulin upon binding of the peptide. Such linker is not only involved in the formation of an hydrophobic pocket to accommodate a bulky peptide residue, but it also provides a positively charged region complementary to a negative charge of the target. This complex of calmodulin with a target not belonging to the kinase family was used to test the residual dipolar coupling (RDC) approach for the determination of calmodulin binding modes to peptides. Although the complex here characterized belongs to the (1--14) family, high Q values were obtained with all the 1:1 complexes for which crystalline structures are available. Reduction of the RDC data set used for the correlation analysis to structured regions of the complex allowed a clear identification of the binding mode. Excluded regions comprise calcium binding loops and loops connecting the EF-hand motifs.
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Affiliation(s)
- Gian Marco Contessa
- Department of Chemical Sciences and Technologies, University of Rome Tor Vergata, via della Ricerca Scientifica, 00133, Rome, Italy
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66
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Kwon SY, Choi YJ, Kang TH, Lee KH, Cha SS, Kim GH, Lee HS, Kim KT, Kim KJ. Highly efficient protein expression and purification using bacterial hemoglobin fusion vector. Plasmid 2005; 53:274-82. [PMID: 15848232 DOI: 10.1016/j.plasmid.2004.11.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2004] [Revised: 10/29/2004] [Accepted: 11/30/2004] [Indexed: 10/25/2022]
Abstract
Recently developed bacterial hemoglobin (VHb) fusion expression vector has been widely used for the production of many target proteins due to its distinctive properties of expressing fusion protein with red color which facilitates visualization of the steps in purification, and increasing solubility of the target proteins. However, after intensive use of the vector, several defects have been found. In this report, we present a modified VHb fusion vector (pPosKJ) with higher efficiency, in which most of the defects were eliminated. First, it was found that thrombin protease often digests target protein as well as inserted thrombin cleavage site, so it was replaced by a TEV cleavage site for more specific cleavage of VHb from target protein. Second, a glycine-rich linker sequence was inserted between 6x his-tag and VHb to improve the affinity of 6x his-tag to Ni-NTA resin, resulting in higher purity of eluted fusion protein. Third, EcoRI and XhoI restriction sites located elsewhere in the vector were removed to make these restriction sites available for the cloning of target protein coding genes. A pPosKJ vector was fully examined with an anti-apoptotic BCL-2 family member of Caenorhabditis elegans, CED-9. A C-terminal VHb fusion expression vector (pPosKJC) was also constructed for stable expression of target proteins that may be difficult to express with an N-terminal fusion. Vaccinia-related kinase 1 (VRK1) was also successfully expressed and purified using the vector with high yield. Taken together, we suggest that the VHb fusion vector may be well suited for high-throughput protein expression and purification.
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Affiliation(s)
- Soo-Young Kwon
- X-ray Research Group, Pohang Accelerator Laboratory, Pohang, Kyungbuk 790-784, Republic of Korea
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67
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Brokx RD, Scheek RM, Weljie AM, Vogel HJ. Backbone dynamic properties of the central linker region of calcium-calmodulin in 35% trifluoroethanol. J Struct Biol 2005; 146:272-80. [PMID: 15099569 DOI: 10.1016/j.jsb.2003.12.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2003] [Revised: 12/16/2003] [Indexed: 10/26/2022]
Abstract
The backbone dynamic properties of uniformly (15)N-labeled calcium-saturated calmodulin (Ca(2+)-CaM) in 35% 2,2,2-trifluoroethanol (TFE) have been examined by (15)N NMR relaxation methods. This particular solvent was chosen in order to mimic the conditions in which CaM was crystallized, which included the presence of alcohols. Special attention was paid to the central linker region of Ca(2+)-CaM, which is a long, solvent-exposed alpha-helix in the crystal structure but is known to be partially unwound and flexible in solution. (15)N T(1), T(2), and (15)N-[(1)H] NOE values were determined for both Ca(2+)-CaM in H(2)O and Ca(2+)-CaM in 35% TFE, and the results indicated that the presence of 35% TFE did indeed induce a more ordered conformation in the central linker, with order parameters for Asp78-Glu80 of 0.29, 0.17, and 0.27 in H(2)O and 0.82, 0.66, and 0.64 in 35% TFE. However, (15)N-[(1)H] NOE values showed that these residues were still slightly more flexible than the rest of the molecule in 35% TFE (Asp78-Glu80 (15)N-[(1)H] NOE=0.46, 0.46, and 0.51). Furthermore, there is still independent motion of the two lobes of Ca(2+)-CaM in 35% TFE, with motional correlation times of approximately 10 and approximately 9 ns for the N- and C-lobes, respectively, indicating that 35% TFE was not sufficient to force Ca(2+)-CaM into a rigid dumbbell-shaped molecule as seen in the crystal structure. Additional factors that could further stabilize the structure of CaM in the crystal include pH, temperature, and crystal packing.
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Affiliation(s)
- Richard D Brokx
- Structural Biology Research Group, Department of Biological Sciences, University of Calgary, 2500 University Dr. N.W., Calgary, Alta., Canada T2N 1N4
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68
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Hobson KF, Housley NA, Pedigo S. Ligand-linked stability of mutants of the C-domain of calmodulin. Biophys Chem 2004; 114:43-52. [PMID: 15792860 DOI: 10.1016/j.bpc.2004.11.002] [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] [Received: 09/10/2004] [Revised: 11/05/2004] [Accepted: 11/05/2004] [Indexed: 10/26/2022]
Abstract
There is a necessary energetic linkage between ligand binding and stability in biological molecules. The critical glutamate in Site 4 was mutated to create two mutants of the C-domain of calmodulin yielding E140D and E140Q. These proteins were stably folded in the absence of calcium, but had dramatically impaired binding of calcium. We determined the stability of the mutant proteins in the absence and presence of calcium using urea-induced unfolding monitored by circular dichroism (CD) spectroscopy. These calcium-dependent unfolding curves were fit to models that allowed for linkage of stability to binding of a single calcium ion to the native and unfolded states. Simultaneous analysis of the unfolding profiles for each mutant yielded estimates for calcium-binding constants that were consistent with results from direct titrations monitored by fluorescence. Binding to the unfolded state was not an important energetic contributor to the ligand-linked stability of these mutants.
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Affiliation(s)
- Kenosha F Hobson
- University of Mississippi, Dept. of Chemistry and Biochemistry, University, MS 38677, USA
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69
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Akyol Z, Bartos JA, Merrill MA, Faga LA, Jaren OR, Shea MA, Hell JW. Apo-Calmodulin Binds with its C-terminal Domain to the N-Methyl-d-aspartate Receptor NR1 C0 Region. J Biol Chem 2004; 279:2166-75. [PMID: 14530275 DOI: 10.1074/jbc.m302542200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calmodulin (CaM) is the major Ca2+ sensor in eukaryotic cells. It consists of four EF-hand Ca2+ binding motifs, two in its N-terminal domain and two in its C-terminal domain. Through a negative feedback loop, CaM inhibits Ca2+ influx through N-methyl-D-aspartate-type glutamate receptors in neurons by binding to the C0 region in the cytosolic tail of the NR1 subunit. Ca2+ -depleted (apo)CaM is pre-associated with a variety of ion channels for fast and effective regulation of channel activities upon Ca2+ influx. Using the NR1 C0 region for fluorescence and circular dichroism spectroscopy studies we found that not only Ca2+ -saturated CaM but also apoCaM bound to NR1 C0. In vitro interaction assays showed that apoCaM also binds specifically to full-length NR1 solubilized from rat brain and to the complete C terminus of the NR1 splice form that contains the C0 plus C2' domain. The Ca2+ -independent interaction of CaM was also observed with the isolated C-but not N-terminal fragment of calmodulin in the independent spectroscopic assays. Fluorescence polarization studies indicated that apoCaM associated via its C-terminal domain with NR1 C0 in an extended conformation and collapsed to adopt a more compact conformation of faster rotational mobility in its complex with NR1 C0 upon addition of Ca2+. Our results indicate that apoCaM is associated with NR1 and that the complex of CaM bound to NR1 C0 undergoes a dramatic conformational change when Ca2+ binds to CaM.
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Affiliation(s)
- Zeynep Akyol
- Department of Biochemistry, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242-1109, USA
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70
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Park KW, Webster DA, Stark BC, Howard AJ, Kim KJ. Fusion protein system designed to provide color to aid in the expression and purification of proteins in Escherichia coli. Plasmid 2003; 50:169-75. [PMID: 14597006 DOI: 10.1016/s0147-619x(03)00046-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We have designed and constructed a new fusion expression vector (pKW32), which contains the His-tagged Vitreoscilla hemoglobin (VHb) coding gene upstream of the multiple cloning site. The pKW32 vector was designed to express target proteins as VHb fusions, which can be purified in one step by affinity chromatography. Due to the color of the heme in VHb, the VHb-fused target proteins have a red color that provides a visual aid for estimating their expression level and solubility. The red color can also be used as a visual marker throughout purification, while the concentration of the fusion protein can be determined by measuring the amount of VHb using carbon monoxide difference spectra. In addition, because of inherently high solubility of VHb, the fusion can increase the solubility of sparingly soluble target proteins. Target proteins can be easily separated from His-tagged VHb due to the presence of a thrombin-cleavage site between them. A mutant VHb, the soluble domain of Vitreoscilla cytochrome bo subunit II, and HIV integrase expressed and purified using the pKW32 system have native function. In addition, the integrase, which is known to be difficult to purify because of low solubility, was purified simply and without solubilizing agents using our system.
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Affiliation(s)
- Kyung-Won Park
- Department of Biological, Chemical, and Physical Sciences, Illinois Institute of Technology, 3101 S Dearborn Chicago, Chicago, IL 60616, USA
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71
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Orsale M, Melino S, Contessa GM, Torre V, Andreotti G, Motta A, Paci M, Desideri A, Cicero DO. Two distinct calcium-calmodulin interactions with N-terminal regions of the olfactory and rod cyclic nucleotide-gated channels characterized by NMR spectroscopy. FEBS Lett 2003; 548:11-6. [PMID: 12885399 DOI: 10.1016/s0014-5793(03)00716-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The interactions of calcium-calmodulin with two fragments of the N-terminal domains of the olfactory alpha-subunit and rod beta-subunit cyclic nucleotide-gated channels have been investigated using nuclear magnetic resonance spectroscopy. The results indicate that in the two cases both the N-terminal and the C-terminal calmodulin lobes are involved in the interaction. The olfactory cyclic nucleotide-gated channel segment forms a 1:1 complex with calmodulin, whereas the rod fragment forms a 2:1 complex. The correlation times of the two complexes, as estimated by (15)N relaxation studies, are compatible with the observed stoichiometries. These results indicate differences in the mode of action by which calmodulin modulates the activity of both channels, and suggest either that the rod channel is modulated through a simultaneous interaction of two beta-subunits with calmodulin or that other regions of the N-terminus are necessarily implicated in the binding.
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Affiliation(s)
- Maria Orsale
- Department of Chemical Sciences and Technologies, University of Rome 'Tor Vergata', via della Ricerca Scientifica, 00133, Rome, Italy
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72
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Forkey JN, Quinlan ME, Shaw MA, Corrie JET, Goldman YE. Three-dimensional structural dynamics of myosin V by single-molecule fluorescence polarization. Nature 2003; 422:399-404. [PMID: 12660775 DOI: 10.1038/nature01529] [Citation(s) in RCA: 323] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2002] [Accepted: 03/03/2003] [Indexed: 11/08/2022]
Abstract
The structural change that generates force and motion in actomyosin motility has been proposed to be tilting of the myosin light chain domain, which serves as a lever arm. Several experimental approaches have provided support for the lever arm hypothesis; however, the extent and timing of tilting motions are not well defined in the motor protein complex of functioning actomyosin. Here we report three-dimensional measurements of the structural dynamics of the light chain domain of brain myosin V using a single-molecule fluorescence polarization technique that determines the orientation of individual protein domains with 20-40-ms time resolution. Single fluorescent calmodulin light chains tilted back and forth between two well-defined angles as the myosin molecule processively translocated along actin. The results provide evidence for lever arm rotation of the calmodulin-binding domain in myosin V, and support a 'hand-over-hand' mechanism for the translocation of double-headed myosin V molecules along actin filaments. The technique is applicable to the study of real-time structural changes in other biological systems.
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Affiliation(s)
- Joseph N Forkey
- Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6083, USA
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73
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Otsuki S, Ikeda A, Sunako T, Muto S, Yazaki J, Nakamura K, Fujii F, Shimbo K, Otsuka Y, Yamamoto K, Sakata K, Sasaki T, Kishimoto N, Kikuchi S, Yamaguchi J. Novel gene encoding a Ca2+-binding protein and under hexokinase-dependent sugar regulation. Biosci Biotechnol Biochem 2003; 67:347-53. [PMID: 12728997 DOI: 10.1271/bbb.67.347] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A cDNA encoding a predicted 15-kDa protein was earlier isolated from sugar-induced genes in rice embryos (Oryza sativa L.) by cDNA microarray analysis. Here we report that this cDNA encodes a novel Ca2+-binding protein, named OsSUR1 (for Oryza sativa sugar-up-regulated-1). The recombinant OsSUR1 protein expressed in Escherichia coli had 45Ca2+-binding activity. Northern analysis showed that the OsSUR1 gene was expressed mainly in the internodes of mature plants and in embryos at an early stage of germination. Expression of the OsSUR1 gene was induced by sugars that could serve as substrates of hexokinase, but expression was not repressed by Ca2+ signaling inhibitors, calmodulin antagonists and inhibitors of protein kinase or protein phosphatase. These results suggested that Os-SUR1 gene expression was stimulated by a hexokinase-dependent pathway not mediated by Ca2+.
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Affiliation(s)
- Shigeo Otsuki
- Division of Biological Sciences, Graduate School of Science, Hokkaido University, Kita-ku N10-W8, Sapporo 060-0810, Japan
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74
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Twine SM, Murphy L, Phillips RS, Callis P, Cash MT, Szabo AG. The Photophysical Properties of 6-Azaindole. J Phys Chem B 2002. [DOI: 10.1021/jp027102r] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Susan M. Twine
- Department of Chemistry, Wilfrid Laurier University, 75 University Ave., Waterloo, Ontario N2L 3C5, Canada, Departments of Chemistry and of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, and Department of Chemistry and Biochemistry, Montana State University, 108 Gaines Hall, Bozeman, Montana 59717
| | - Lise Murphy
- Department of Chemistry, Wilfrid Laurier University, 75 University Ave., Waterloo, Ontario N2L 3C5, Canada, Departments of Chemistry and of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, and Department of Chemistry and Biochemistry, Montana State University, 108 Gaines Hall, Bozeman, Montana 59717
| | - Robert S. Phillips
- Department of Chemistry, Wilfrid Laurier University, 75 University Ave., Waterloo, Ontario N2L 3C5, Canada, Departments of Chemistry and of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, and Department of Chemistry and Biochemistry, Montana State University, 108 Gaines Hall, Bozeman, Montana 59717
| | - Patrik Callis
- Department of Chemistry, Wilfrid Laurier University, 75 University Ave., Waterloo, Ontario N2L 3C5, Canada, Departments of Chemistry and of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, and Department of Chemistry and Biochemistry, Montana State University, 108 Gaines Hall, Bozeman, Montana 59717
| | - Michael T. Cash
- Department of Chemistry, Wilfrid Laurier University, 75 University Ave., Waterloo, Ontario N2L 3C5, Canada, Departments of Chemistry and of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, and Department of Chemistry and Biochemistry, Montana State University, 108 Gaines Hall, Bozeman, Montana 59717
| | - Arthur G. Szabo
- Department of Chemistry, Wilfrid Laurier University, 75 University Ave., Waterloo, Ontario N2L 3C5, Canada, Departments of Chemistry and of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, and Department of Chemistry and Biochemistry, Montana State University, 108 Gaines Hall, Bozeman, Montana 59717
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75
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VanScyoc WS, Sorensen BR, Rusinova E, Laws WR, Ross JBA, Shea MA. Calcium binding to calmodulin mutants monitored by domain-specific intrinsic phenylalanine and tyrosine fluorescence. Biophys J 2002; 83:2767-80. [PMID: 12414709 PMCID: PMC1302361 DOI: 10.1016/s0006-3495(02)75286-7] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Cooperative calcium binding to the two homologous domains of calmodulin (CaM) induces conformational changes that regulate its association with and activation of numerous cellular target proteins. Calcium binding to the pair of high-affinity sites (III and IV in the C-domain) can be monitored by observing calcium-dependent changes in intrinsic tyrosine fluorescence intensity (lambda(ex)/lambda(em) of 277/320 nm). However, calcium binding to the low-affinity sites (I and II in the N-domain) is more difficult to measure with optical spectroscopy because that domain of CaM does not contain tryptophan or tyrosine. We recently demonstrated that calcium-dependent changes in intrinsic phenylalanine fluorescence (lambda(ex)/lambda(em) of 250/280 nm) of an N-domain fragment of CaM reflect occupancy of sites I and II (VanScyoc, W. S., and M. A. Shea, 2001, Protein Sci. 10:1758-1768). Using steady-state and time-resolved fluorescence methods, we now show that these excitation and emission wavelength pairs for phenylalanine and tyrosine fluorescence can be used to monitor equilibrium calcium titrations of the individual domains in full-length CaM. Calcium-dependent changes in phenylalanine fluorescence specifically indicate ion occupancy of sites I and II in the N-domain because phenylalanine residues in the C-domain are nonemissive. Tyrosine emission from the C-domain does not interfere with phenylalanine fluorescence signals from the N-domain. This is the first demonstration that intrinsic fluorescence may be used to monitor calcium binding to each domain of CaM. In this way, we also evaluated how mutations of two residues (Arg74 and Arg90) located between sites II and III can alter the calcium-binding properties of each of the domains. The mutation R74A caused an increase in the calcium affinity of sites I and II in the N-domain. The mutation R90A caused an increase in calcium affinity of sites III and IV in the C-domain whereas R90G caused an increase in calcium affinity of sites in both domains. This approach holds promise for exploring the linked energetics of calcium binding and target recognition.
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Affiliation(s)
- Wendy S VanScyoc
- Department of Biochemistry, University of Iowa College of Medicine, 51 Newton Road, Iowa City, IA 52242, USA
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76
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El Mezgueldi M, Tang N, Rosenfeld SS, Ostap EM. The kinetic mechanism of Myo1e (human myosin-IC). J Biol Chem 2002; 277:21514-21. [PMID: 11940582 DOI: 10.1074/jbc.m200713200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Myo1e is the widely expressed subclass-1 member of the myosin-I family. We performed a kinetic analysis of a truncated myo1e that consists of the motor and the single IQ motif with a bound calmodulin. We determined the rates and equilibrium constants for the key steps in the ATPase cycle. The maximum actin activated ATPase rate (V(max)) and the actin concentration at half-maximum of V(max) (K(ATPase)) of myo1e are similar to those of the native protein. The K(ATPase) is low (approximately 1 microm), however the affinity of myo1e for actin in the presence of ATP is very weak. A weak actin affinity and a rapid rate of phosphate release result in a pathway under in vitro assay conditions in which phosphate is released while myo1e is dissociated from actin. Actin activation of the ATPase activity and the low K(ATPase) are the result of actin activation of ADP release. We propose that myo1e is tuned to function in regions of high concentrations of cross-linked actin filaments. Additionally, we found that ADP release from actomyo1e is > 10-fold faster than other vertebrate myosin-I isoforms. We propose that subclass-1 myosin-Is are tuned for rapid sliding, whereas subclass-2 isoforms are tuned for tension maintenance or stress sensing.
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Affiliation(s)
- Mohammed El Mezgueldi
- Department of Physiology and The Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6085, USA
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77
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Camas A, Cárdenas L, Quinto C, Lara M. Expression of different calmodulin genes in bean (Phaseolus vulgaris L.): role of nod factor on calmodulin gene regulation. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2002; 15:428-436. [PMID: 12036273 DOI: 10.1094/mpmi.2002.15.5.428] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Three calmodulin (PvCaM-1, PvCaM-2, and PvCaM-3) clones were isolated from a Phaseolus vulgaris nodule cDNA library. All clones contain the complete coding region and are 62 to 74% homologous within this region. Compared to plant CaM consensus sequences, PvCaM-2 has a novel tyrosine118 residue, representing a putative phosphorylation site. Southern analysis suggested that calmodulin is encoded by a gene family. These three CaM clones are expressed mainly in young tissues and meristems. The expression pattern of PvCaM-2 and PvCaM-3 is almost identical but different from that of PvCaM-1, suggesting that PvCaM-1 is a well-defined CaM gene, whereas PvCaM-2 and PvCaM-3 could be alleles. PvCaM clones are expressed early in nodules, and transcript levels increase from nodule primordia to nodule-like structures induced by the Nod factor. Conversely, in roots, Nod factor lowers mRNA levels of all three PvCaM clones, but especially of PvCaM-1. Inhibition of PvCaM-1 expression also is observed when 2,3,5-triiodobenzoic acid is added and is prevented when roots are treated with indole-3-acetic acid, suggesting that PvCaM-1 regulation is related to the Nod factor inhibition of polar auxin transport. These results could suggest that CaM clones do not participate in the early signaling generated by the Nod factor but do participate in early events of nodule formation.
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Affiliation(s)
- Alberto Camas
- Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos
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78
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Szymanski PT, Szymanska G, Goyal RK. Differences in calmodulin and calmodulin-binding proteins in phasic and tonic smooth muscles. Am J Physiol Cell Physiol 2002; 282:C94-C104. [PMID: 11742802 DOI: 10.1152/ajpcell.00257.2001] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To determine whether densities of calmodulin (CaM) and CaM-binding proteins are related to phasic and tonic behavior of smooth muscles, we quantified these proteins in the opossum esophageal body (EB) and lower esophageal sphincter (LES), which represent phasic and tonic smooth muscles, respectively. Gel electrophoresis, immunoprecipitation, Western blot, and hemagglutinin epitope-tagged CaM (HA-CaM) overlay assay with quantitative scanning densitometry and phosphorylation measurements were used. Total protein content in the two smooth muscles was similar (approximately 30 mg protein/g frozen tissue). Total tissue concentration of CaM was significantly (25%) higher in EB than in LES (P < 0.05). HA-CaM-binding proteins were qualitatively similar in LES and EB extracts. Myosin, myristoylated alanine-rich C kinase substrate protein, Ca(2+)/CaM kinase II, and calponin contents were also similar in the two muscles. However, content and total activity of myosin light chain kinase (MLCK) and content of caldesmon (CaD) were three- to fourfold higher in EB than in LES. Increased CaM and MLCK content may allow for a wide range of contractile force varying from complete relaxation in the basal state to a large-amplitude, high-velocity contraction in EB phasic muscle. Increased content of CaD, which provides a braking mechanism on contraction, may further contribute to the phasic contractile behavior. In contrast, low CaM, MLCK, and CaD content may be responsible for a small range of contractile force seen in tonic muscle of LES.
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Affiliation(s)
- Pawel T Szymanski
- Center for Swallowing and Motility Disorders, Harvard Medical School, West Roxbury, Massachusetts 02132, USA
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79
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Traxler KW, Norcum MT, Hainfeld JF, Carlson GM. Direct visualization of the calmodulin subunit of phosphorylase kinase via electron microscopy following subunit exchange. J Struct Biol 2001; 135:231-8. [PMID: 11722163 DOI: 10.1006/jsbi.2001.4411] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Calmodulin is a tightly bound, intrinsic subunit (delta) of the hexadecameric phosphorylase-b kinase holoenzyme, (alphabetagammadelta)4. To introduce specifically labeled calmodulin into the phosphorylase-b kinase complex for its eventual visualization by electron microscopy, we have developed a method for rapidly exchanging exogenous calmodulin for the intrinsic delta subunit. This method exploits previous findings that low concentrations of urea in the absence of Ca(2+) ions cause the specific dissociation of only the delta subunit from the holoenzyme [Paudel, H. K., and Carlson, G. M. (1990) Biochem. J. 268, 393-399]. In the current study, phosphorylase-b kinase was incubated with excess exogenous calmodulin and a threshold concentration of urea to promote exchange of its delta subunit with the exogenous calmodulin. Size exclusion HPLC was then used to remove the excess calmodulin from the holoenzyme containing exchanged delta subunits. Using metabolically labeled [35S]calmodulin to allow quantification and optimization of exchange conditions, we achieved exchange of approximately 10% of all delta subunits within 1 h, with the exchanged holoenzyme retaining full catalytic activity. Calmodulins derivatized with Nanogold for visualization by scanning transmission electron microscopy were then exchanged for delta, which for the first time allowed localization of the delta subunit within the bridged, bilobal phosphorylase b kinase holoenzyme complex. The delta subunits were determined to be near the edge of the lobes, just distal to the interlobal bridges and proximal to a previously identified region of the enzyme's catalytic gamma subunit.
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Affiliation(s)
- K W Traxler
- Department of Chemistry, Bemidji State University, Bemidji, Minnesota 56601, USA
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80
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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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81
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Schmalzigaug R, Ye Q, Berchtold MW. Calmodulin protects cells from death under normal growth conditions and mitogenic starvation but plays a mediating role in cell death upon B-cell receptor stimulation. Immunology 2001; 103:332-42. [PMID: 11454062 PMCID: PMC1783242 DOI: 10.1046/j.1365-2567.2001.01259.x] [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: 11/20/2022] Open
Abstract
Calmodulin (CaM) is the main intracellular Ca2+ sensor protein responsible for mediating Ca2+ triggered processes. Chicken DT40 lymphoma B cells express CaM from the two genes, CaMI and CaMII. Here we report the phenotypes of DT40 cells with the CaMII gene knocked out. The disruption of the CaMII gene causes the intracellular CaM level to decrease by 60%. CaMII-/- cells grow more slowly and die more frequently as compared to wild type (wt) cells but do not exhibit significant differences in their cell cycle profile. Both phenotypes are more pronounced at reduced serum concentrations. Upon stimulation of the B-cell receptor (BCR), the resting Ca2+ levels remain elevated after the initial transient in CaMII-/- cells. Despite higher Ca2+ resting levels, the CaMII-/- cells are partially protected from BCR induced apoptosis indicating that CaM plays a dual role in apoptotic processes.
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Affiliation(s)
- R Schmalzigaug
- Department of Molecular Cell Biology, Institute of Molecular Biology, University of Copenhagen, Denmark
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82
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Simão RC, Gomes SL. Structure, expression, and functional analysis of the gene coding for calmodulin in the chytridiomycete Blastocladiella emersonii. J Bacteriol 2001; 183:2280-8. [PMID: 11244068 PMCID: PMC95135 DOI: 10.1128/jb.183.7.2280-2288.2001] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The single calmodulin (CaM) gene and the corresponding cDNA of the chytridiomycete Blastocladiella emersonii were isolated and characterized. The CaM gene is interrupted by three introns and transcribed in a single 0.7-kb mRNA species encoding a predicted protein 91% identical to human CaM. B. emersonii CaM has been expressed in Escherichia coli as a fusion protein with gluthatione S-transferase (GST) and purified by affinity chromatography and cleavage from the GST portion using a site-specific protease. In the presence of Ca(2+), B. emersonii CaM exhibited a shift in apparent molecular mass similar to that observed with bovine CaM and was able to activate the autophosphorylation of CaM-dependent protein kinase II (CaMKII) from rat brain. CaM expression is developmentally regulated in B. emersonii, with CaM mRNA and protein concentrations increasing during sporulation to maximum levels observed just prior to the release of the zoospores into the medium. Both CaM protein and mRNA levels decrease drastically at the zoospore stage, increasing again during germination. The CaM antagonists compound 48/80, calmidazolium, and W7 were shown to completely inhibit B. emersonii sporulation when added to the cultures at least 120, 150, and 180 min after induction, respectively. All these drugs also inhibited growth and zoospore production in this fungus. The Ca(2+) channel blocker TMB-8 and the CaMKII inhibitor KN93 completely inhibited sporulation if added up to 60 min after induction of this stage, but only KN93 affected fungal growth. The data presented suggest that the Ca(2+)-CaM complex and CaMKII play an important role during growth and sporulation in B. emersonii.
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Affiliation(s)
- R C Simão
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP 05508-900, Brazil
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83
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Tarcsa E, Szymanska G, Lecker S, O'Connor CM, Goldberg AL. Ca2+-free calmodulin and calmodulin damaged by in vitro aging are selectively degraded by 26 S proteasomes without ubiquitination. J Biol Chem 2000; 275:20295-301. [PMID: 10791958 DOI: 10.1074/jbc.m001555200] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ubiquitin-proteasome pathway is believed to selectively degrade post-synthetically damaged proteins in eukaryotic cells. To study this process we used calmodulin (CaM) as a substrate because of its importance in cell regulation and because it acquires isoaspartyl residues in its Ca(2+)-binding regions both in vivo and after in vitro "aging" (incubation for 2 weeks without Ca(2+)). When microinjected into Xenopus oocytes, in vitro aged CaM was degraded much faster than native CaM by a proteasome-dependent process. Similarly, in HeLa cell extracts aged CaM was degraded at a higher rate, even though it was not conjugated to ubiquitin more rapidly than the native species. Ca(2+) stimulated the ubiquitination of both species, but inhibited their degradation. Thus, for CaM, ubiquitination and proteolysis appear to be dissociated. Accordingly, purified muscle 26 S proteasomes could degrade aged CaM and native Ca(2+)-free (apo) CaM without ubiquitination. Addition of Ca(2+) dramatically reduced degradation of the native molecules but only slightly reduced the breakdown of the aged species. Thus, upon Ca(2+) binding, native CaM assumes a non-degradable conformation, which most of the age-damaged species cannot assume. Thus, flexible conformations, as may arise from age-induced damage or the absence of ligands, can promote degradation directly by the proteasome without ubiquitination.
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Affiliation(s)
- E Tarcsa
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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84
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Takahashi S, Katagiri T, Yamaguchi-Shinozaki K, Shinozaki K. An Arabidopsis gene encoding a Ca2+-binding protein is induced by abscisic acid during dehydration. PLANT & CELL PHYSIOLOGY 2000; 41:898-903. [PMID: 10965948 DOI: 10.1093/pcp/pcd010] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
An Arabidopsis thaliana RD20 cDNA, which was isolated as one of drought-inducible genes, encodes a putative protein with a conserved EF-hand Ca2+-binding domain. The recombinant RD20 protein was shown to bind Ca2+. The transcription of RD20 gene was induced not only by drought but also by ABA and high salinity.
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Affiliation(s)
- S Takahashi
- Laboratory of Plant Molecular Biology, RIKEN, Tsukuba Life Science Center, Ibaraki, Japan
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85
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Jaren OR, Harmon S, Chen AF, Shea MA. Paramecium calmodulin mutants defective in ion channel regulation can bind calcium and undergo calcium-induced conformational switching. Biochemistry 2000; 39:6881-90. [PMID: 10841769 DOI: 10.1021/bi000037w] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Calmodulin (CaM) is an essential eukaryotic protein that binds calcium ions cooperatively at four EF-hand binding sites to regulate signal transduction pathways. Interactions between the apo domains of vertebrate CaM reduce the calcium affinities of sites I and II below their intrinsic values, allowing sequential opening of the two hydrophobic clefts in CaM. Viable domain-specific mutants of Parameciumcalmodulin (PCaM) differentially affect ion channels and provide a unique opportunity to dissect the roles of the two highly homologous half-molecule domains. Calcium binding induced an increase in the level of ordered secondary structure and a decrease in Stokes radius in these mutants; such changes were identical in direction to those of wild type CaM, but the magnitude depended on the mutation. Calcium titrations monitored by changes in the intrinsic fluorescence of Y138 in site IV showed that the affinities of sites III and IV of wild type PCaM were (i) higher than those of the same sites in rat CaM, (ii) equivalent to those of the same sites in PCaM mutants altered between sites I and II, and (iii) higher than those of PCaM mutants modified in sites III and IV. Thus, calcium saturation drove all mutants to undergo conformational switching in the same direction but not to the same extent as wild type PCaM. The disruption of the allosteric mechanism that is manifest as faulty channel regulation may be explained by altered properties of switching among the 14 possible partially saturated species of PCaM rather than by an inability to adopt two end-state conformations or target interactions similar to those of the wild type protein.
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Affiliation(s)
- O R Jaren
- Department of Biochemistry, University of Iowa College of Medicine, Iowa City, Iowa 52242-1109, USA
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86
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Hou J, Putkey JA, Hecht JT. Delta 469 mutation in the type 3 repeat calcium binding domain of cartilage oligomeric matrix protein (COMP) disrupts calcium binding. Cell Calcium 2000; 27:309-14. [PMID: 11013461 DOI: 10.1054/ceca.2000.0125] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Cartilage oligomeric matrix protein (COMP/TSP5), a large glycoprotein found in the territorial matrix surrounding chondrocytes, is the fifth member of the thrombospondin (TSP) gene family. While the function of COMP is unknown, its importance is underscored by the finding that mutations in the highly conserved type 3 repeat domain causes two skeletal dysplasias. Pseudoachondroplasia (PSACH) and Multiple Epiphyseal Dysplasia, Fairbanks type (EDM1). The type 3 repeats are highly conserved low-affinity Ca(2+)binding domains that are found in all TSP genes. This study was undertaken to determine the effects of mutations on calcium binding and structure of the type 3 repeat domains. Wild-type (WT) and Delta469 recombinant COMP (rCOMP) proteins containing the entire calcium-binding domain were expressed in E. coli and purified. Equilibrium dialysis demonstrated that WT bound 10-12 Ca(2+)ions/molecule while Delta469 bound approximately half the Ca(2+)ions. Circular dichroism (CD) spectrometry had striking spectral changes for the WT in response to increasing concentrations of Ca(2+). These CD spectral changes were cooperative and reversible. In contrast, a large CD spectral change was not observed at any Ca(2+)concentration for Delta469. Moreover, both WT and Delta469 proteins produced similar CD spectral changes when titrated with Zn(2+), Cu(2+)and Ni(2+)indicating that the Delta469 mutation specifically affects only calcium binding. These results suggest that the Delta469 mutation, in the type 3 repeat region, interferes with Ca(2+)binding and that filling of all Ca(2+)binding loops may be critical for correct COMP protein conformation.
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Affiliation(s)
- J Hou
- Department of Pediatrics, University of Texas Houston Medical School, Houston, USA
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87
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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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88
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Abstract
By using (35)S-labeled calmodulin (CaM), we have isolated a full-length cDNA clone expressing the Schizosaccharomyces pombe homologue of calmodulin kinase I (CaMK-I), a gene we have named cmk1. It has been previously been shown in mammals that CaMK-I is a member of a CaM-dependent protein kinase cascade that ultimately regulates transcription factors such as ATF and cAMP-response element-binding protein. The cmk1 cDNA encodes a 335-amino acid protein with significant homology to mammalian CaMK-I, including a conserved sequence for phosphorylation by CaM kinase kinase. We have expressed the cmk1 cDNA in bacteria and yeast, and we have shown that it is a CaM-dependent protein kinase. A truncation mutant of cmk1 (d320) failed to bind CaM, indicating that the CaM-binding domain is at the extreme C terminus of the protein. The mRNA for cmk1 is expressed in a cell cycle-dependent manner, peaking at or near the G(1)/S boundary. Overexpression of wild-type cmk1 in S. pombe caused no apparent effects on growth and division. However, mutation of a predicted regulatory site (Thr-192) to aspartic acid resulted in hyperactivation of CMK1 activity in the presence of CaM and causes cell cycle arrest in vivo. Arrest is also accompanied by morphological defects. These results suggest the presence of a CaM-dependent protein kinase cascade in yeast and indicate that cmk1 may be important in cell cycle progression, a process known to be dependent on CaM in eukaryotic cells.
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Affiliation(s)
- C D Rasmussen
- Department of Anatomy, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E5, Canada
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89
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Kong Au T, Chow Leung P. Identification of the binding and inhibition sites in the calmodulin molecule for ophiobolin A by site-directed mutagenesis. PLANT PHYSIOLOGY 1998; 118:965-73. [PMID: 9808741 PMCID: PMC34807 DOI: 10.1104/pp.118.3.965] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Ophiobolin A, a fungal toxin that affects maize and rice, has previously been shown to inhibit calmodulin by reacting with the lysine (Lys) residues in the calmodulin. In the present study we mutated Lys-75, Lys-77, and Lys-148 in the calmodulin molecule by site-directed mutagenesis, either by deleting them or by changing them to glutamine or arginine. We found that each of these three Lys residues could bind one molecule of ophiobolin A. Normally, only Lys-75 and Lys-148 bind ophiobolin A. Lys-77 seemed to be blocked by the binding of ophiobolin A to Lys-75. Lys-75 is the primary binding site and is responsible for all of the inhibition of ophiobolin A. When Lys-75 was removed, Lys-77 could then react with ophiobolin A to produce inhibition. Lys-148 was shown to be a binding site but not an inhibition site. The Lys-75 mutants were partially resistant to ophiobolin A. When both Lys 75 and Lys-77 or all three Lys residues were mutated, the resulting calmodulins were very resistant to ophiobolin A. Furthermore, Lys residues added in positions 86 and/or 143 (which are highly conserved in plant calmodulins) did not react with ophiobolin A. None of the mutations seemed to affect the properties of calmodulin. These results show that ophiobolin A reacts quite specifically with calmodulin.
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Affiliation(s)
- T Kong Au
- Department of Zoology, The University of Hong Kong, Pokfulam Road, Hong Kong
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90
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Szymanska G, Leszyk JD, O'Connor CM. Carboxyl methylation of deamidated calmodulin increases its stability in Xenopus oocyte cytoplasm. Implications for protein repair. J Biol Chem 1998; 273:28516-23. [PMID: 9774482 DOI: 10.1074/jbc.273.43.28516] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The widely distributed protein-L-isoaspartate(D-aspartate) O-methyltransferase (PIMT; EC 2.1.1.77) is postulated to play a role in the repair or metabolism of damaged cellular proteins containing L-isoaspartyl residues derived primarily from the spontaneous deamidation of protein asparaginyl residues. To evaluate the functional consequence of PIMT-catalyzed methylation on the stability of isoaspartyl-containing proteins in cells, Xenopus laevis oocytes were microinjected with both deamidated and nondeamidated forms of recombinant chicken calmodulin (CaM) containing a hemagglutinin (HA) epitope at its N terminus. Processing of HA-CaM was monitored by electrophoretic analysis and Western blotting of oocyte extracts. The experiments indicate that deamidated HA-CaM is degraded after microinjection, while nondeamidated HA-CaM is stable. Kinetic analysis is consistent with the entry of microinjected HA-CaM into two intracellular pools with distinct hydrolytic stabilities. The larger, more stable pool may consist of HA-CaM bound to the heterogeneous pool of oocyte CaM binding proteins detected by an overlay procedure. Enzymatic methylation of deamidated HA-CaM with purified PIMT prior to injection results in its stabilization. Conversely, inhibition of endogenous oocyte PIMT with sinefungin, a nonhydrolyzable analog of S-adenosylhomocysteine, increases the rate of deamidated HA-CaM degradation. These results are consistent with a role for PIMT-catalyzed methylation in the repair of damaged cellular proteins.
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Affiliation(s)
- G Szymanska
- Department of Biology, Boston College, Chestnut Hill, Massachusetts 02167-3811, USA
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91
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O'Connor MB, O'Connor CM. Complex interactions of the protein L-isoaspartyl methyltransferase and calmodulin revealed with the yeast two-hybrid system. J Biol Chem 1998; 273:12909-13. [PMID: 9582322 DOI: 10.1074/jbc.273.21.12909] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The widely distributed protein-L-isoaspartyl, D-aspartyl carboxylmethyltransferase (EC 2.1.1.77) is hypothesized to play a role in the repair or metabolism of deamidated and isomerized proteins that are spontaneously generated during the aging of proteins in cells. The yeast two-hybrid system was used to identify proteins that potentially interact with the methyltransferase in a cellular processing pathway. Two cDNAs, both encoding calmodulin, were isolated from a human fetal brain cDNA library using the human methyltransferase as the bait. Enzymatic assays with purified components revealed a complex set of interactions between the methyltransferase and calmodulin. Calmodulin weakly stimulated protein carboxylmethyltransferase activity in vitro at concentrations of the two proteins reflecting their representation in mammalian brain. Calmodulin stimulation of methyltransferase was observed in both the presence and absence of calcium, although the effect was greater in the presence of calcium. Native calmodulin was not a substrate for the carboxylmethyltransferase, but deamidated variants of calmodulin act as substrates for the methyltransferase, with calculated Km values of 3.6 and 8.6 microM for calcium-liganded and unliganded calmodulin, respectively. Both the effector and substrate interactions of calmodulin with the protein isoaspartyl methyltransferase likely contributed to the positive results obtained with the two-hybrid system.
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Affiliation(s)
- M B O'Connor
- Department of Biology, Boston College, Chestnut Hill, Massachusetts 02167-3811, USA
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92
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Hayashi N, Matsubara M, Takasaki A, Titani K, Taniguchi H. An expression system of rat calmodulin using T7 phage promoter in Escherichia coli. Protein Expr Purif 1998; 12:25-8. [PMID: 9473453 DOI: 10.1006/prep.1997.0807] [Citation(s) in RCA: 128] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
An efficient expression system of rat calmodulin in Escherichia coli is presented. To express rat calmodulin cDNA, we employed a pET expression vector which contains the T7 phage promoter and terminator. After transformation of E. coli BL21(DE3) strain which carries T7 phage RNA polymerase inducible with isopropyl-beta-D-thiogalactopyranoside, induction of the expression, and chromatography of soluble proteins on a phenyl-Sepharose column, about 250 mg of recombinant rat calmodulin was obtained from 1 liter of E. coli culture. The recombinant calmodulin lacked the N-terminal methionine, and posttranslational modifications such as Nalpha-acetylation and methylation. This system facilitates the large amount preparation of calmodulin and the mutant proteins required for the structural analysis by NMR spectrometry and/or X-ray crystallography.
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Affiliation(s)
- N Hayashi
- Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi, 470-11, Japan.
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93
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Szymanska G, O'Connor MB, O'Connor CM. Construction of an epitope-tagged calmodulin useful for the analysis of calmodulin-binding proteins: addition of a hemagglutinin epitope does not affect calmodulin-dependent activation of smooth muscle myosin light chain kinase. Anal Biochem 1997; 252:96-105. [PMID: 9324946 DOI: 10.1006/abio.1997.2319] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
An epitope-tagged calmodulin (CaM), capable of interacting with CaM-binding proteins in cellular extracts, would be a valuable tool for identifying proteins in signal transduction pathways involving calcium. A bacterial overexpression vector for epitope-tagged CaM has been constructed by inserting the coding sequence for a nine amino acid portion of the influenza virus hemagglutinin (HA) protein into the initiation site of an overexpression vector for chicken CaM. The HA-CaM fusion produced in bacteria was compared to native CaM for its ability to activate smooth muscle myosin light chain kinase (MLCK), one of the best understood CaM-dependent enzymes. MLCK activity was tested in both a purified system and a CaM-depleted "native actomyosin" preparation maintaining many of the regulatory properties of the intact smooth muscle. HA-CaM behaves identically to unmodified CaM in both systems, indicating that the HA epitope does not adversely affect CaM function. The recombinant HA-CaM was used to sensitively detect CaM interactions with smooth muscle proteins in a modified gel overlay assay, using a monoclonal antibody against the HA epitope as the secondary reagent. Enzymatically active complexes of HA-CaM and MLCK could be immunoprecipitated from actomyosin preparations using the same monoclonal antibody and protein G-Sepharose beads.
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Affiliation(s)
- G Szymanska
- Department of Biology, Boston College, Chestnut Hill, Massachusetts 02167-3811, USA
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94
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Browne JP, Strom M, Martin SR, Bayley PM. The role of beta-sheet interactions in domain stability, folding, and target recognition reactions of calmodulin. Biochemistry 1997; 36:9550-61. [PMID: 9236001 DOI: 10.1021/bi970460d] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Single-residue mutations have been made of the hydrophobic Ile or Val residue in position 8 of each of the four calcium-binding loop sequences (sites I-IV) of Drosophila calmodulin. These highly conserved residues are part of the hydrophobic core of either calmodulin domain and are involved in the structural link of two calcium-binding sites via a short antiparallel beta-sheet. In the apo-form, the replacement of Ile (or Val) by Gly causes a significant destabilization, shown by the unfolding of the secondary structure of the domain carrying the mutation. In the presence of calcium, the deficiency in alpha-helical structure at 20 degrees C is restored for the mutants at site I, II, or III but not at site IV, which requires the further binding of a high-affinity target peptide to re-establish the native conformation. The extent of the destabilization is seen in the depression of the melting temperature of individual domains, which can be as large as 80 degrees C in the case of Ca4-CaM(V136G). However, because of low values of the unfolding enthalpy for calmodulin domains, only relatively low values of <2 kcal/mol are implied for DeltaDeltaG, the free energy of destabilization due to mutation. Consistent with this, the secondary structure of any unfolded mutant domain is highly sensitive to solvent composition and is largely refolded in the presence of 12.5% (v/v) aqueous trifluoroethanol. Compared to wild-type calmodulin, the affinities of the mutants for calcium and target peptides from sk-MLCK at 20 degrees C are significantly reduced but the effects are relatively small. These results indicate that the conformation of calmodulin can be dramatically altered by mutation of a single highly conserved residue but that changes in solvent or the binding of a target sequence can readily compensate for this, restoring the wild-type properties. The results also suggest that the integrity of both the apo- and holo-forms of calmodulin is important for the maintenance of its biological function and confirm the importance of conserving the structural function of the residues involved in the beta-sheet interactions.
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Affiliation(s)
- J P Browne
- Division of Physical Biochemistry, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, U.K
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95
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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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96
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Nakashima K, Maekawa H, Yazawa M. Chimeras of yeast and chicken calmodulin demonstrate differences in activation mechanisms of target enzymes. Biochemistry 1996; 35:5602-10. [PMID: 8611552 DOI: 10.1021/bi952586l] [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: 01/31/2023]
Abstract
Various chimeric proteins were constructed from yeast (Saccharomyces cerevisiae) and chicken calmodulin (CaM), and regions essential for target activation and responsible for the specific features of the yeast CaM were identified. The chimeric CaMs were designed so that each Ca2+ binding site of the yeast CaM was replaced in series from the C-terminus. Resulting CaM proteins showed Ca2+ binding properties inherent to the original Ca2+ binding site. Cooperative Ca2+ binding and a suitable rearrangement of the two EF-hand sites in each half-molecular domain were shown to be important for high-affinity interaction with CaM-dependent cyclic nucleotide phosphodiesterase (PDE). Residues in chicken CaM sequences 129-148 and 88-128, respectively, were required for low values of Kact (the concentration of CaM required for the half-maximal activation) in the activation of PDE and myosin light chain kinase (skMLCK and smMLCK). The difference in the structural requirements indicated different manners of the interaction. While PDE was activated to similar levels by different chimeras, the maximum activity (Vmax) given by chicken CaMs was not achieved by any chimeric CaMs in MLCKs. Residues in chicken CaM sequences 1-50 and 88-129, in addition to Ca2+ binding to the fourth site, were important for high values of Vmax of skMLCK. On the other hand, Met51 and residues in chicken CaM sequence 88-129 were critical for the high Vmax of smMLCK. These residues may work to form the active structure of the catalytic site of each MLCK, while simple binding of CaM seems sufficient to expose the active site of PDE.
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Affiliation(s)
- K Nakashima
- Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, Japan
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97
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Shea MA, Verhoeven AS, Pedigo S. Calcium-induced interactions of calmodulin domains revealed by quantitative thrombin footprinting of Arg37 and Arg106. Biochemistry 1996; 35:2943-57. [PMID: 8608132 DOI: 10.1021/bi951934g] [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: 01/31/2023]
Abstract
Calcium-dependent conformational states of calmodulin (CaM) were probed by thrombin to determine quantitative differences in the susceptibility of two bonds: Arg37-Ser38 (R37-S38, near site I in the N-terminal domain) and Arg106-His107 (R106-H107, near site III in the C-terminal domain). Quantitative thrombin footprinting of a discontinuous equilibrium calcium titration of wild-type calmodulin showed that the R37-S38 bond of the apoprotein was cleaved at a barely detectable level while the R106-H107 bond was maximally susceptible. Calcium binding to sites III and IV monotonically protected R106-H107 from proteolysis; concomitantly, the susceptibility of R37-S38 increased. However, calcium binding to sites I and II protected R37-S38 from cleavage, yielding a peaked biphasic profile composed of equal and opposite transitions. Both bonds were fully protected when calmodulin was saturated with calcium. Susceptibility profiles resolved from the fractional abundance of primary cleavage products (peptides 1-37, 38-148, 1-106, 107-148) were interpreted as directly reflecting calcium-induced conformational changes in whole calmodulin; free energies of calcium binding and cooperativity were estimated. Secondary cleavage was never observed; both R37 and R106 were sites of thrombinolysis in whole calmodulin only. In studies of E140Q-CaM (having a mutation in site IV), the susceptibility of R37-S38 decreased monotonically. Thus, the biphasic character of cleavage of R37 in helix B was not intrinsic to that domain but depended on propagation of effects of calcium-induced changes in the C-terminal domain. The observed patterns of susceptibility indicated that partially saturated wild-type calmodulin adopts at least one intermediate conformation whose structure is determined by calcium-mediated interactions between the domains.
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Affiliation(s)
- M A Shea
- Department of Biochemistry, University of Iowa College of Medicine, Iowa City, 52242-1109, USA
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98
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Ehrhardt MR, Erijman L, Weber G, Wand AJ. Molecular recognition by calmodulin: pressure-induced reorganization of a novel calmodulin-peptide complex. Biochemistry 1996; 35:1599-605. [PMID: 8634291 DOI: 10.1021/bi951267r] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The interaction of apocalmodulin (apoCaM) with a peptide (Neurop) based on the primary sequence of the calmodulin-binding domain of neuromodulin has been studied by fluorescence spectroscopy. The 1:1 complex (12 microM) formed between apoCaM and the Neurop peptide is extremely sensitive to salt and is half dissociated in less than 0.1 M KCl, suggesting that electrostatic interactions contribute strongly to complex formation. Ion pair interactions are frequently sensitive to high hydrostatic pressure due to electrostriction effects in the solvated ion state. Application of high pressure to the apoCaM.Neurop complex causes a red shift of the Neurop tryptophan emission center of mass and a reduced residual anisotropy but with insignificant reduction in quantum yield. The transition is smooth, reversible, and apparently two-state with a midpoint pressure of approximately 0.8 kbar. The residual anisotropy, quantum yield, and center of mass of the emission spectrum are consistent with the movement of the tryptophan side chain to a more solvated, slightly less restricted environment upon the pressure-induced transition. The pressure effect is independent of the concentration of the complex. These and other data are consistent with the pressure-induced reorganization being a unimolecular event not requiring dissociation of the complex. A volume change of approximately 66 mL mol-1 and a free energy change of approximately 1.7 kcal mol-1 are associated with the reorganization. The residual interactions maintaining the complex under high pressure are characterized by low standard molar volume and/or high standard free energy changes upon disruption but are destroyed by 200 mM KCl. It is postulated that the main effect of salt on the complex at high pressure is to drive the collapse of the hydrophobic pocket to which the peptide is binding.
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Affiliation(s)
- M R Ehrhardt
- Department of Biochemistry, University of Illinois at Urbana-Champaign 61801, USA
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99
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Moser MJ, Lee SY, Klevit RE, Davis TN. Ca2+ binding to calmodulin and its role in Schizosaccharomyces pombe as revealed by mutagenesis and NMR spectroscopy. J Biol Chem 1995; 270:20643-52. [PMID: 7657644 DOI: 10.1074/jbc.270.35.20643] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
As a first step toward identifying the important structural elements of calmodulin from Schizosaccharomyces pombe, we examined the ability of heterologous calmodulins and Ca(2+)-binding site mutant S. pombe calmodulins to replace the essential cam1+ gene. A cDNA encoding vertebrate calmodulin allows growth of S. pombe. However, calmodulin from Saccharomyces cerevisiae does not support growth even though the protein is produced at high levels. With one exception, all mutant S. pombe calmodulins with one or more intact Ca(2+)-binding sites allow growth at 21 degrees C. A mutant containing only an intact Ca(2+)-binding site 3 fails to support growth, as does S. pombe calmodulin with all four Ca(2+)-binding sites mutated. Several of the mutant proteins confer a temperature-sensitive phenotype. Analysis of the degree of temperature sensitivity allows the Ca(2+)-binding sites to be ranked by their ability to support fission yeast proliferation. Site 2 is more important than site 1, which is more important than site 4, which is more important than site 3. A visual colony color screen based on the fission yeast ade1+ gene was developed to perform these genetic analyses. To compare the Ca(2+)-binding properties of individual sites to their functional importance for viability, Ca2+ binding to calmodulin from S. pombe was studied by 1H NMR spectroscopy. NMR analysis indicates a Ca(2+)-binding profile that differs from those previously determined for vertebrate and S. cerevisiae calmodulins. Ca(2+)-binding site 3 has the highest relative affinity for Ca2+, while the affinities of sites 1, 2, and 4 are indistinguishable. A combination of an in vivo functional assay and an in vitro physical assay reveals that the relative affinity of a site for Ca2+ does not predict its functional importance.
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Affiliation(s)
- M J Moser
- Department of Biochemistry SJ-70, University of Washington, Seattle 98195, USA
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100
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Pedigo S, Shea MA. Discontinuous equilibrium titrations of cooperative calcium binding to calmodulin monitored by 1-D 1H-nuclear magnetic resonance spectroscopy. Biochemistry 1995; 34:10676-89. [PMID: 7654722 DOI: 10.1021/bi00033a044] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Calmodulin binds up to four calcium ions cooperatively in response to cellular signaling events. To understand the functional energetics of calcium activation of calmodulin, it is important to monitor individual Ca(2+)-binding sites and other positions at partial degrees of saturation. This study is the first use of 1-D proton NMR to monitor the equilibrium Ca(2+)-binding properties of calmodulin. Protein concentrations required for NMR experiments (approximately 1 mM) are approximately 1000-fold greater than the Kd values for calcium binding to calmodulin, preventing a direct continuous equilibrium titration of calmodulin. Thus, dialysates of calmodulin in buffers of experimentally determined [Ca2+]free were prepared to conduct discontinuous equilibrium titrations at both 92 and 152 mM KCl. For the C-terminal domain, the normalized area of the delta-protons of Y138 defined calcium binding isotherms. For N-terminal domain resonances (F16C delta H, T26C alpha H, D64C alpha H, and F65C delta H), the calcium-dependent change in chemical shift defined isotherms. These are the first residue-specific studies to monitor the energetics of Ca2+ binding to the N-terminal domain in wild-type holo calmodulin. Calcium binding to both domains appeared cooperative and binding affinity decreased in higher KCl. Isotherms resolved from the side chain resonances of F16 and F65 had a lower median ligand activity and a slightly higher degree of cooperativity than isotherms resolved from the backbone resonances of D64 and T26. Salt-dependent changes in apparent intradomain cooperativity differed for the domains: at higher salt, delta Gc increased for the C-terminal domain while remaining constant or decreasing for the N-terminal domain.
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Affiliation(s)
- S Pedigo
- Department of Biochemistry, University of Iowa College of Medicine, Iowa City 52242-1109, USA
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