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Utilization of a calmodulin lysine methyltransferase co-expression system for the generation of a combinatorial library of post-translationally modified proteins. Protein Expr Purif 2012; 86:83-8. [PMID: 23036357 DOI: 10.1016/j.pep.2012.09.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2012] [Revised: 09/20/2012] [Accepted: 09/21/2012] [Indexed: 11/22/2022]
Abstract
By successfully incorporating sequence diversity into proteins, combinatorial libraries have been a staple technology used in protein engineering, directed evolution, and synthetic biology for generating proteins with novel specificities and activities. However, these approaches mostly overlook the incorporations of post-translational modifications, which nature extensively uses for modulating protein activities in vivo. As an initial step of incorporating post-translational modifications into combinatorial libraries, we present a bacterial co-expression system, utilizing a recently characterized calmodulin methyltransferase (CaM KMT), to trimethylate a combinatorial library of the calmodulin central linker region. We show that this system is robust, with the successful over-expression and post-translational modification performed in Escherichia coli. Furthermore we show that trimethylation differentially affected the conformational dynamics of the protein upon the binding of calcium, and the thermal stability of the apoprotein. Collectively, these data support that when applied to an appropriately designed protein library scaffold, CaM KMT is able to produce a post-translationally modified library of protein sequences, thus providing a powerful tool for future protein library designs and constructions.
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2
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Bradley LH, Bricken ML, Randle C. Expression, purification, and characterization of proteins from high-quality combinatorial libraries of the mammalian calmodulin central linker. Protein Expr Purif 2010; 75:186-91. [PMID: 20732425 DOI: 10.1016/j.pep.2010.08.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Revised: 08/11/2010] [Accepted: 08/14/2010] [Indexed: 11/28/2022]
Abstract
Combinatorial libraries offer an attractive approach towards exploring protein sequence, structure and function. Although several strategies introduce sequence diversity, the likelihood of identifying proteins with novel functions is increased when the library of genes encodes for folded and soluble structures. Here we present the first application of the binary patterning approach of combinatorial protein library design to the unique central linker region of the highly-conserved protein, calmodulin (CaM). We show that this high-quality approach translates very well to the CaM protein scaffold: all library members over-express and are functionally diverse, having a range of conformations in the presence and absence of calcium as determined by circular dichroism spectroscopy. Collectively, these data support that the binary patterning approach, when applied to the highly-conserved protein fold, can yield large collections of folded, soluble and highly-expressible proteins.
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Affiliation(s)
- Luke H Bradley
- Department of Anatomy & Neurobiology and the Morris K. Udall Center of Parkinson's Disease Research Excellence, University of Kentucky College of Medicine, Lexington, KY 40536, USA.
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Li S, Xie L, Ma Z, Zhang R. cDNA cloning and characterization of a novel calmodulin-like protein from pearl oyster Pinctada fucata. FEBS J 2005; 272:4899-910. [PMID: 16176264 DOI: 10.1111/j.1742-4658.2005.04899.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Calcium metabolism in oysters is a very complicated and highly controlled physiological and biochemical process. However, the regulation of calcium metabolism in oyster is poorly understood. Our previous study showed that calmodulin (CaM) seemed to play a regulatory role in the process of oyster calcium metabolism. In this study, a full-length cDNA encoding a novel calmodulin-like protein (CaLP) with a long C-terminal sequence was identified from pearl oyster Pinctada fucata, expressed in Escherichia coli and characterized in vitro. The oyster CaLP mRNA was expressed in all tissues tested, with the highest levels in the mantle that is a key organ involved in calcium secretion. In situ hybridization analysis reveals that CaLP mRNA is expressed strongly in the outer and inner epithelial cells of the inner fold, the outer epithelial cells of the middle fold, and the dorsal region of the mantle. The oyster CaLP protein, with four putative Ca(2+)-binding domains, is highly heat-stable and has a potentially high affinity for calcium. CaLP also displays typical Ca(2+)-dependent electrophoretic shift, Ca(2+)-binding activity and significant Ca(2+)-induced conformational changes. Ca(2+)-dependent affinity chromatography analysis demonstrated that oyster CaLP was able to interact with some different target proteins from those of oyster CaM in the mantle and the gill. In summary, our results have demonstrated that the oyster CaLP is a novel member of the CaM superfamily, and suggest that the oyster CaLP protein might play a different role from CaM in the regulation of oyster calcium metabolism.
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Affiliation(s)
- Shuo Li
- Institute of Marine Biotechnology, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, China
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4
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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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5
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Vetter SW, Leclerc E. Novel aspects of calmodulin target recognition and activation. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:404-14. [PMID: 12542690 DOI: 10.1046/j.1432-1033.2003.03414.x] [Citation(s) in RCA: 264] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Several crystal and NMR structures of calmodulin (CaM) in complex with fragments derived from CaM-regulated proteins have been reported recently and reveal novel ways for CaM to interact with its targets. This review will discuss and compare features of the interaction between CaM and its target domains derived from the plasma membrane Ca2+-pump, the Ca2+-activated K+-channel, the Ca2+/CaM-dependent kinase kinase and the anthrax exotoxin. Unexpected aspects of CaM/target interaction observed in these complexes include: (a) binding of the Ca2+-pump domain to only the C-terminal part of CaM (b) dimer formation with fragments of the K+-channel (c) insertion of CaM between two domains of the anthrax exotoxin (d) binding of Ca2+ ions to only one EF-hand pair and (e) binding of CaM in an extended conformation to some of its targets. The mode of interaction between CaM and these targets differs from binding conformations previously observed between CaM and peptides derived from myosin light chain kinase (MLCK) and CaM-dependent kinase IIalpha (CaMKIIalpha). In the latter complexes, CaM engulfs the CaM-binding domain peptide with its two Ca2+-binding lobes and forms a compact, ellipsoid-like complex. In the early 1990s, a model for the activation of CaM-regulated proteins was developed based on this observation and postulated activation through the displacement of an autoinhibitory or regulatory domain from the target protein upon binding of CaM. The novel structures of CaM-target complexes discussed here demonstrate that this mechanism of activation may be less general than previously believed and seems to be not valid for the anthrax exotoxin, the CaM-regulated K+-channel and possibly also not for the Ca2+-pump.
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Affiliation(s)
- Stefan W Vetter
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA.
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6
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Joseph JD, Means AR. Calcium binding is required for calmodulin function in Aspergillus nidulans. EUKARYOTIC CELL 2002; 1:119-25. [PMID: 12455978 PMCID: PMC118048 DOI: 10.1128/ec.01.1.119-125.2002] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To explore the structural basis for the essential role of calmodulin (CaM) in Aspergillus nidulans, we have compared the biochemical and in vivo properties of A. nidulans CaM (AnCaM) with those of heterologous CaMs. Neither Saccharomyces cerevisiae CaM (ScCaM) nor a Ca2+ binding mutant of A. nidulans CaM (1234) interacts appreciably with A. nidulans CaM binding proteins by an overlay assay or activates two essential CaMKs, CMKA and CMKB. In contrast, although vertebrate CaM (VCaM) binds a spectrum of proteins similar to that for AnCaM, it is unable to fully activate CMKA and CMKB, displaying a higher K(CaM) and reduced Vmax for both enzymes. In correlation with the biochemical analysis, neither ScCaM nor 1234 can support A. nidulans growth in the absence of the endogenous protein, whereas VCaM only partially complements the absence of wild-type CaM. Analysis of VCaM and AnCaM chimeras demonstrates that amino acid variations in both N- and C-terminal domains contribute to the inability of VCaM to activate CMKB, but differences in the N terminus are largely responsible for the reduced activity towards CMKA. In vivo, the chimeric molecules support growth equivalently, but only to levels intermediate between those of VCaM and AnCaM, suggesting that the reduced ability to activate the CaMKs is not solely responsible for the inability of VCaM to complement the absence of the wild-type protein. Thus, not only is Ca2+ binding required for CaM function in A. nidulans, but the essential in vivo functions of A. nidulans CaM are uniquely sensitive to the subtle amino acid variations present in vertebrate CaM.
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Affiliation(s)
- James D Joseph
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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Atreya HS, Sahu SC, Bhattacharya A, Chary KV, Govil G. NMR derived solution structure of an EF-hand calcium-binding protein from Entamoeba Histolytica. Biochemistry 2001; 40:14392-403. [PMID: 11724551 DOI: 10.1021/bi0114978] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We present the three-dimensional (3D) solution structure of a calcium-binding protein from Entamoeba histolytica (EhCaBP), an etiologic agent of amoebiasis affecting millions worldwide. EhCaBP is a 14.7 kDa (134 residues) monomeric protein thought to play a role in the pathogenesis of amoebiasis. The 3D structure of Ca(2+)-bound EhCaBP has been derived using multidimensional nuclear magnetic resonance (NMR) spectroscopic techniques. The study reveals the presence of two globular domains connected by a flexible linker region spanning 8 amino acid residues. Each domain consists of a pair of helix-loop-helix motifs similar to the canonical EF-hand motif of calcium-binding proteins. EhCaBP binds to four Ca(2+) with high affinity (two in each domain), and it is structurally related to calmodulin (CaM) and troponin C (TnC) despite its low sequence homology ( approximately 29%) with these proteins. NMR-derived structures of EhCaBP converge within each domain with low RMSDs and angular order-parameters for backbone torsion angles close to 1.0. However, the presence of a highly flexible central linker region results in an ill-defined orientation of the two domains relative to one other. These findings are supported by backbone (15)N relaxation rate measurements and deuterium exchange studies, which reveal low structural order parameters for residues in the central linker region. Earlier, biochemical studies showed that EhCaBP is involved in a novel signal transduction mechanism, distinct from CaM. A possible reason for such a functional diversity is revealed by a detailed comparison of the 3D structure of EhCaBP with that of CaM and TnC. The studies indicate a more open C-terminal domain for EhCaBP with larger water exposed total hydrophobic surface area as compared to CaM and TnC. Further dissimilarities between the structures include the presence of two Gly residues (G63 and G67) in the central linker region of EhCaBP, which seem to impart it a greater flexibility compared to CaM and TnC and also play crucial role in its biological function. Thus, unlike in CaM and TnC, wherein the length and/or composition of the central linker have been found to be crucial for their function, in EhCaBP, both flexibility as well as amino acid composition is required for the function of the protein.
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Affiliation(s)
- H S Atreya
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai-400005, India
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Medvedeva MV, Djemuchadze DR, Watterson DM, Marston SB, Gusev NB. Replacement of Lys-75 of calmodulin affects its interaction with smooth muscle caldesmon. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1544:143-50. [PMID: 11341924 DOI: 10.1016/s0167-4838(00)00213-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The interaction of smooth muscle caldesmon with synthetic calmodulin (SynCam) and its five mutants with replacement of Lys-75 was analyzed by means of intrinsic Trp fluorescence, zero-length crosslinking and by caldesmon-induced inhibition of actomyosin ATPase activity. SynCam and its double mutant with replacement K75P and simultaneous insertion of KGK between residues 80 and 81 have a comparably low affinity to caldesmon and the probability of crosslinking of this mutant to caldesmon was the lowest among all mutants analyzed. SynCam and its double mutant (K75P+KGK) induced nearly complete reversion of caldesmon inhibition of actomyosin ATPase activity with half-maximal reversion achieved at about 1 microM. Two mutants, K75A and K75V, with partially stabilized less positive central domain have higher affinity to caldesmon. These mutants induce 80-85% reversion of caldesmon inhibition of actomyosin ATPase and the half-maximal reversion was achieved at about 0.3-0.4 microM. Two last mutants, K75P and K75E, with distorted central domain have high affinity to caldesmon and the probability of crosslinking of K75P to caldesmon was the highest among calmodulin mutants tested. These mutants induced complete reversion of caldesmon inhibition with half-maximal effect observed at 0.3-0.4 microM. We suggest that the length, flexibility and charge of the central domain affect binding of calmodulin mutants and their ability to reverse caldesmon-induced inhibition of actomyosin ATPase activity.
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Affiliation(s)
- M V Medvedeva
- Department of Biochemistry, School of Biology, Mascow State University, Russia
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Corti C, Leclerc L'Hostis E, Quadroni M, Schmid H, Durussel I, Cox J, Dainese Hatt P, James P, Carafoli E. Tyrosine phosphorylation modulates the interaction of calmodulin with its target proteins. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 262:790-802. [PMID: 10411641 DOI: 10.1046/j.1432-1327.1999.00441.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The activation of six target enzymes by calmodulin phosphorylated on Tyr99 (PCaM) and the binding affinities of their respective calmodulin binding domains were tested. The six enzymes were: myosin light chain kinase (MLCK), 3'-5'-cyclic nucleotide phosphodiesterase (PDE), plasma membrane (PM) Ca2+-ATPase, Ca2+-CaM dependent protein phosphatase 2B (calcineurin), neuronal nitric oxide synthase (NOS) and type II Ca2+-calmodulin dependent protein kinase (CaM kinase II). In general, tyrosine phosphorylation led to an increase in the activatory properties of calmodulin (CaM). For plasma membrane (PM) Ca2+-ATPase, PDE and CaM kinase II, the primary effect was a decrease in the concentration at which half maximal velocity was attained (Kact). In contrast, for calcineurin and NOS phosphorylation of CaM significantly increased the Vmax. For MLCK, however, neither Vmax nor Kact were affected by tyrosine phosphorylation. Direct determination by fluorescence techniques of the dissociation constants with synthetic peptides corresponding to the CaM-binding domain of the six analysed enzymes revealed that phosphorylation of Tyr99 on CaM generally increased its affinity for the peptides.
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Affiliation(s)
- C Corti
- Protein Chemistry Laboratory, Department of Biology, Swiss Federal Institute of Technology, (ETH) Zürich
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10
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Okano H, Cyert MS, Ohya Y. Importance of phenylalanine residues of yeast calmodulin for target binding and activation. J Biol Chem 1998; 273:26375-82. [PMID: 9756868 DOI: 10.1074/jbc.273.41.26375] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recent genetic studies of yeast calmodulin (yCaM) have shown that alterations of different sets of Phe residues result in distinct functional defects (Ohya, Y., and Botstein, D. (1994) Science 263, 963-966). To examine the importance of Phe residues for target binding and activation, we purified mutant yCaMs containing single or double Phe to Ala substitutions and determined their ability to bind and activate two target proteins, calcineurin and CaM-dependent protein kinase (CaMK). Binding assays using the gel overlay technique and quantitative analyses using surface plasmon resonance measurements indicated that the binding of yCaM to calcineurin is impaired by either double mutations of F16A/F19A or a single mutation of F140A, while binding to CaMK is impaired by F89A, F92A, or F140A. These same mutant yCaMs fail to activate calcineurin and CaMK, respectively, in vitro. In addition, F19A exhibited a severe defect in activation of both enzymes. F12A activated calcineurin to only 50% of the level achieved by wild-type calmodulin but fully activated CaMK. These results suggest that each target protein requires a specific and distinct subset of Phe residues in yCaM for target binding and activation.
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Affiliation(s)
- H Okano
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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Tabernero L, Taylor DA, Chandross RJ, VanBerkum MF, Means AR, Quiocho FA, Sack JS. The structure of a calmodulin mutant with a deletion in the central helix: implications for molecular recognition and protein binding. Structure 1997; 5:613-22. [PMID: 9195880 DOI: 10.1016/s0969-2126(97)00217-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND Calmodulin (CaM) is the major calcium-dependent regulator of a large variety of important intracellular processes in eukaryotes. The structure of CaM consists of two globular calcium-binding domains joined by a central 28-residue alpha helix. This linker helix has been hypothesized to act as a flexible tether and is crucial for the binding and activation of numerous target proteins. Although the way in which alterations of the central helix modulate the molecular recognition mechanism is not known exactly, the relative orientation of the globular domains seems to be of great importance. The structural analysis of central helix mutants may contribute to a better understanding of how changes in the conformation of CaM effect its function. RESULTS We have determined the crystal structure of a calcium-saturated mutant of chicken CaM (mut-2) that lacks two residues in the central helix, Thr79 and Asp80, at 1.8 A resolution. The mutated shorter central helix is straight, relative to that of the wild-type structure. The loss of a partial turn of the central alpha helix causes the C-terminal domain to rotate 220 degrees around the helix axis, with respect to the N-terminal domain. This rotation places the two domains on the same side of the central helix, in a cis orientation, rather than in the trans orientation found in wild-type structures. CONCLUSIONS The deletion of two residues in the central helix of CaM does not distort or cause a bending of the linker alpha helix. The main consequence of the mutation is a change in the relative orientation of the two globular calcium-binding domains, causing the hydrophobic patches in these domains to be closer and much less accessible to interact with the target enzymes. This may explain why this mutant of CaM shows a marked decrease in its ability to activate some enzymes while the mutation has little or no effect on its ability to activate others.
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Affiliation(s)
- L Tabernero
- Department of Macromolecular Crystallography Bristol-Myers Squibb Pharmaceutical Research Institute Princeton, NJ 08543-4000, USA
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Chin D, Sloan DJ, Quiocho FA, Means AR. Functional consequences of truncating amino acid side chains located at a calmodulin-peptide interface. J Biol Chem 1997; 272:5510-3. [PMID: 9038155 DOI: 10.1074/jbc.272.9.5510] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
To test the relevance of the calmodulin-peptide crystal structures to their respective calmodulin-enzyme interactions, amino acid side chains in calmodulin were altered at positions that interact with the calmodulin-binding peptide of smooth muscle myosin light chain kinase but not with the calmodulin kinase IIalpha peptide. Since shortening the side chains of Trp-800, Arg-812, and Leu-813 in smooth muscle myosin light chain kinase abrogated calmodulin-dependent activation (Bagchi, I. C., Huang, Q., and Means, A. R. (1992) J. Biol. Chem. 267, 3024-3029), substitutions were introduced at positions in calmodulin which contact residues corresponding to Arg-812 and Leu-813 in the smooth muscle myosin light chain kinase peptide. Assays of smooth muscle myosin light chain kinase with the calmodulin mutants M51A,V55A, L32A,M51A,V55A, and L32A,M51A,V55A,F68L, M71A exhibited 60%, 25%, and less than 1% of maximal activity respectively, whereas the mutants fully activated calmodulin kinase IIalpha. Alanine substitutions at positions on the smooth muscle myosin light chain kinase peptide, corresponding to Trp-800 and Arg-812 in the enzyme, produced an 8-fold increase in the enzyme inhibition constant in contrast with the abolition of calmodulin binding by similar mutations in the parent enzyme.
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Affiliation(s)
- D Chin
- Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710, USA
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Persechini A, Stemmer PM, Ohashi I. Localization of unique functional determinants in the calmodulin lobes to individual EF hands. J Biol Chem 1996; 271:32217-25. [PMID: 8943279 DOI: 10.1074/jbc.271.50.32217] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have investigated the functional interchangeability of EF hands I and III or II and IV, which occupy structurally analogous positions in the native I-II and III-IV EF hand pairs of calmodulin. Our approach was to functionally characterize four engineered proteins, made by replacing in turn each EF hand in one pair by a duplicate of its structural analog in the other. In this way functional determinants we define as unique were localized to the component EF hands in each pair. Replacement of EF hand I by III reduces calmodulin-dependent activation of cerebellar nitric oxide synthase activity by 50%. Replacement of EF hand IV by II reduces by 60% activation of skeletal muscle myosin light chain kinase activity. There appear to be no major unique determinants for activation of these enzyme activities in the other EF hands. Replacement of EF hand III by I or IV by II reduces by 50-80% activation of smooth muscle myosin light chain kinase activity, and replacement of EF hand I by III or II by IV reduces by 90% activation of this enzyme activity. Thus, calmodulin-dependent activation of each of the enzyme activities examined, even the closely related kinases, is dependent upon a distinct pattern of unique determinants in the four EF hands of calmodulin. All the engineered proteins examined bind four Ca2+ ions with high affinity. Comparison of the Ca2+-binding properties of native and engineered CaMs indicates that the Ca2+-binding affinity of an engineered I-IV EF hand pair and a native I-II pair are similar, but an engineered III-II EF hand pair is intermediate in affinity to the native III-IV and I-II pairs, minimally suggesting that EF hands I and III contain unique determinants for the formation and function of EF hand pairs. The residues directly coordinating Ca2+ ion appear to play little or no role in establishing the different Ca2+-binding properties of the EF hand pairs in calmodulin.
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Affiliation(s)
- A Persechini
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA.
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14
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Persechini A, Gansz KJ, Paresi RJ. Activation of myosin light chain kinase and nitric oxide synthase activities by engineered calmodulins with duplicated or exchanged EF hand pairs. Biochemistry 1996; 35:224-8. [PMID: 8555178 DOI: 10.1021/bi952383x] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We have constructed three engineered calmodulins (CaMs) in which the two EF hand pairs have been substituted for one another or exchanged: CaMNN, the C-terminal EF hand pair (residues 82-148) has been replaced by a duplication of the N-terminal pair (residues 9-75); CaMCC, the N-terminal pair has been replaced by a duplication of the C-terminal pair; CaMCN, the two EF had pairs have been exchanged. Skeletal muscle myosin light chain kinase (skMLCK) activity is activated to 75% of the maximum level by CaMCC and to 45% of the maximum level by CaMCN and is not significantly activated by CaMNN; Kact or Ki values for the engineered CaMs are 2-3.5 nM. Smooth muscle myosin light chain kinase activity (gMLCK) is fully activated by CaMCN and is not significantly activated by either CaMNN or CaMCC; the Kact value for CaMCN is 2 nM and the Ki values for CaMNN and CaMCC are 10 and 40 nM, respectively. Cerebellar nitric oxide synthase activity (nNOS) is fully activated by CaMNN and CaMCN and is not significantly activated by CaMCC; the engineered CaMs have Kact or Ki values for this enzyme activity of 2-8 nM. These results indicate that the EF hand pairs contain distinct but overlapping sets of determinants for binding and activation of enzymes, with the greater degree of overlap in determinants for binding. Furthermore, while the structural changes associated with swapping the EF hand pairs do not affect activation of nNOS or gMLCK activities, they significantly reduce activation of skMLCK activity, indicating that this process requires specific determinants in CaM outside the EF hand pairs.
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Affiliation(s)
- A Persechini
- Department of Physiology, University of Rochester Medical Center, New York 14642, USA
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15
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Ho G, Chen TL, Chisholm RL. Both the amino and carboxyl termini of Dictyostelium myosin essential light chain are required for binding to myosin heavy chain. J Biol Chem 1995; 270:27977-81. [PMID: 7499275 DOI: 10.1074/jbc.270.46.27977] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Dictyostelium myosin deficient in the essential light chain (ELC) does not function normally either in vivo or in vitro (Pollenz, R. S., Chen, T. L., Trivinos-Lagos, L., and Chisholm, R. L. (1992) Cell 69, 951-962). Since normal myosin function requires association of ELC, we investigated the domains of ELC that are necessary for binding to the myosin heavy chain (MHC). Deleting the NH2-terminal 11 or 28 amino acid residues (delta N11 or delta N28) or the COOH-terminal 15 amino acid residues (delta C15) abolished binding of the ELC to the MHC when the mutants were expressed in wild-type (WT) cells. In contrast, the ELC carrying deletion or insertion of four amino acid residues (D4 or I4) in the central linker segment bound the MHC in WT cells, although less efficient competition with WT ELC suggested that the affinity for the MHC is reduced. When these mutants were expressed in ELC-minus (mlcE-) cells, where the binding to the heavy chain is not dependent on efficient competition with the endogenous ELC, delta N28 and delta N11 bound to the MHC at 15% of WT levels and delta C15 did not bind to a significant degree. I4 and D4, however, bound with normal stoichiometry. These data indicate that residues at both termini of the ELC are required for association with the MHC, while the central linker domain appears to be less critical for binding. When the mutants were analyzed for their ability to complement the cytokinesis defect displayed by mlcE- cells, a correlation to the level of ELC carried by the MHC was observed, indicating that a stoichiometric ELC-MHC association is necessary for normal myosin function in vivo.
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Affiliation(s)
- G Ho
- Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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16
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Meador WE, George SE, Means AR, Quiocho FA. X-ray analysis reveals conformational adaptation of the linker in functional calmodulin mutants. NATURE STRUCTURAL BIOLOGY 1995; 2:943-5. [PMID: 7583665 DOI: 10.1038/nsb1195-943] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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17
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Edman CF, George SE, Means AR, Schulman H, Yaswen P. Selective activation and inhibition of calmodulin-dependent enzymes by a calmodulin-like protein found in human epithelial cells. EUROPEAN JOURNAL OF BIOCHEMISTRY 1994; 226:725-30. [PMID: 7528142 DOI: 10.1111/j.1432-1033.1994.tb20101.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A calmodulin-like protein, which is identical in size and 85% identical to vertebrate calmodulin, was recently identified by 'subtractive hybridization' comparison of transcripts expressed in normal versus transformed human mammary epithelial cells. Unlike the ubiquitous distribution of calmodulin, calmodulin-like protein expression is restricted to certain epithelial cells, and appears to be modulated during differentiation. In addition, calmodulin-like protein levels are often significantly reduced in malignant tumor cells as compared to corresponding normal epithelial cells. The current studies compare calmodulin-like protein functions with those of calmodulin. We find that calmodulin-like protein activation of multifunctional Ca2+/calmodulin-dependent protein kinase II (calmodulin kinase II) is equivalent to activation by calmodulin, but that four other calmodulin-dependent enzymes, cGMP phosphodiesterase, calcineurin, nitric-oxide synthase, and myosin-light-chain kinase, display much weaker activation by calmodulin-like protein than by calmodulin. In the case of myosin-light-chain kinase, calmodulin-like protein competitively inhibits calmodulin activation of the enzyme with a Ki value of 170 nM. Thus, calmodulin-like protein may have evolved to function as a specific agonist of certain calmodulin-dependent enzymes, and/or as a specific competitive antagonist of other calmodulin-dependent enzymes.
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Affiliation(s)
- C F Edman
- Life Sciences Division, Lawrence Berkeley Laboratory, CA 94720
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18
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Role of domain 3 of calmodulin in activation of calmodulin-stimulated phosphodiesterase and smooth muscle myosin light chain kinase. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(19)89456-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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19
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Persechini A, McMillan K, Leakey P. Activation of myosin light chain kinase and nitric oxide synthase activities by calmodulin fragments. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)33985-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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20
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Zhang M, Huque E, Vogel H. Characterization of trimethyllysine 115 in calmodulin by 14N and 13C NMR spectroscopy. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)37660-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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21
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da Silva EF, Sorenson MM, Smillie LB, Barrabin H, Scofano HM. Comparison of calmodulin and troponin C with and without its amino-terminal helix (residues 1-11) in the activation of erythrocyte Ca(2+)-ATPase. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)74303-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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22
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Calmodulin-cardiac troponin C chimeras. Effects of domain exchange on calcium binding and enzyme activation. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)74590-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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23
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Paul S, Ebadi M. Vasoactive intestinal peptide: its interactions with calmodulin and catalytic antibodies. Neurochem Int 1993; 23:197-214. [PMID: 8220166 DOI: 10.1016/0197-0186(93)90111-h] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- S Paul
- Department of Anesthesiology, University of Nebraska Medical Center, Omaha 68198-6830
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24
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Bayley PM, Martin SR. The alpha-helical content of calmodulin is increased by solution conditions favouring protein crystallisation. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1160:16-21. [PMID: 1420330 DOI: 10.1016/0167-4838(92)90034-b] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The conformation of porcine-brain calmodulin in solution has been examined by far-UV circular dichroism in the presence of 2-methyl 2,4-pentanediol, and polyethylene glycol which are used to promote the crystallisation of calmodulin. These organic compounds increase the alpha-helical content of Ca4-calmodulin to a significant degree and to a level similar to the alpha-helical content deduced from the crystal structure. These results support the view that in aqueous solution at pH 5-7, the conformation of Ca4-calmodulin is significantly different from the crystal structure and probably lacks at least a portion of the central helix. In the process of crystallisation, Ca4-calmodulin apparently adopts additional alpha-helical structure, probably due to the composition of the solution from which crystals are grown.
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Affiliation(s)
- P M Bayley
- Division of Physical Biochemistry, National Institute for Medical Research, Mill Hill, London, UK
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25
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Meador WE, Means AR, Quiocho FA. Target enzyme recognition by calmodulin: 2.4 A structure of a calmodulin-peptide complex. Science 1992; 257:1251-5. [PMID: 1519061 DOI: 10.1126/science.1519061] [Citation(s) in RCA: 837] [Impact Index Per Article: 26.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The crystal structure of calcium-bound calmodulin (Ca(2+)-CaM) bound to a peptide analog of the CaM-binding region of chicken smooth muscle myosin light chain kinase has been determined and refined to a resolution of 2.4 angstroms (A). The structure is compact and has the shape of an ellipsoid (axial ratio approximately 2:1). The bound CaM forms a tunnel diagonal to its long axis that engulfs the helical peptide, with the hydrophobic regions of CaM melded into a single area that closely covers the hydrophobic side of the peptide. There is a remarkably high pseudo-twofold symmetry between the closely associated domains. The central helix of the native CaM is unwound and expanded into a bend between residues 73 and 77. About 185 contacts (less than 4 A) are formed between CaM and the peptide, with van der Waals contacts comprising approximately 80% of this total.
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Affiliation(s)
- W E Meador
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, TX 77030
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26
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Abstract
The linker regions of the central helices of calmodulin and of troponin C are observed to be alpha-helices in crystal and in solution. However, these linkers are predicted to be non-helical by standard algorithms. Further, there is strong evidence that when calmodulin interacts with some of its targets this linker helix bends. The linker appears to be delicately balanced between helical and non-helical conformations. A review of this subject suggests that one can anticipate more unpredicted conformations for the central helices of the score of other proteins that have four EF-hand domains.
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Affiliation(s)
- R H Kretsinger
- Department of Biology, University of Virginia, Charlottesville
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27
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Regulation of the erythrocyte Ca(2+)-ATPase by mutant calmodulins with Glu—-Ala substitutions in the Ca(2+)-binding domains. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42848-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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28
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Three amino acid substitutions in domain I of calmodulin prevent the activation of chicken smooth muscle myosin light chain kinase. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54665-2] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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29
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Takrama JF, Graves DJ. Solution conformations of the N-terminal CNBr fragment of glycogen phosphorylase and its interaction with calmodulin. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1077:371-8. [PMID: 2029536 DOI: 10.1016/0167-4838(91)90553-c] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The CNBr peptides, CBPa and CBPb, corresponding to the N-terminal 1-91 amino acid residues of glycogen-phosphorylase a and b, respectively, were purified and characterized. CD, 31P-NMR and fluorescence spectroscopy were used to assess the structural organization of the cyanogen bromide peptides in solution. The cyanogen bromide peptides yielded 21% of alpha-helical structures by CD compared to a calculated value of 36.3%. These peptides interact with calmodulin which induces measurable alpha-helices in the cyanogen bromide peptides. The helix stabilizing reagent, trifluoroethanol, induces high numbers of alpha-helices in CBP, thereby demonstrating the conformation fluidity of this peptide. The dissociation constants for calmodulin and CBP estimated by fluorescence titrations were 36.0 and 29.9 nM for CBPb in the presence of Ca2+ and EGTA, respectively. The phosphorylated residue in CBPa causes a decrease in binding interactions with calmodulin and corresponding values obtained for CBPa by fluorescence titration are 56.0 and 141.0 nM, respectively. The Ser-P-14 of CBPa is titratable, yielding a pKa = 5.45 and a Hill coefficient of 1.5. A helical wheel analysis using a computer program in PC/GENE of the CBP shows that peptide stretches in the alpha-1 and alpha-2 helices are most basic and fairly amphiphilic and therefore represent the most probable segment for CaM binding. It is this structural character of these segments which presumably confer the ability to bind CaM and facilitate some of the allosteric transitions of glycogen phosphorylase.
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Affiliation(s)
- J F Takrama
- Department of Biochemistry and Biophysics, Iowa State University, Ames 50011
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30
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Sun GH, Ohya Y, Anraku Y. Half-calmodulin is sufficient for cell proliferation. Expressions of N- and C-terminal halves of calmodulin in the yeast Saccharomyces cerevisiae. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(20)89602-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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31
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Sheng ZL, Francois JM, Hitchcock-DeGregori SE, Potter JD. Effects of mutations in the central helix of troponin C on its biological activity. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(19)67653-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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32
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Fluorescent adducts of wheat calmodulin implicate the amino-terminal region in the activation of skeletal muscle myosin light chain kinase. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)77183-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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33
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Rasmussen C, Means R, Lu K, May G, Means A. Characterization and expression of the unique calmodulin gene of Aspergillus nidulans. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)77415-2] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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34
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Kink JA, Maley ME, Preston RR, Ling KY, Wallen-Friedman MA, Saimi Y, Kung C. Mutations in paramecium calmodulin indicate functional differences between the C-terminal and N-terminal lobes in vivo. Cell 1990; 62:165-74. [PMID: 2163766 DOI: 10.1016/0092-8674(90)90250-i] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We examined calmodulin and its gene from the wild-type and viable mutants of P. tetraurelia. The mutants, selected for their behavioral aberrations, have little or no defects in growth rates, secretion, excretion, or motility. They can be grouped according to whether they underreact or overreact behaviorally to certain stimuli, reflecting their respective loss of either a Ca2(+)-dependent Na+ current or a Ca2(+)-dependent K+ current. Sequence analyses showed that all three underreactors have amino acid substitutions in the N-terminal lobe of the calmodulin dumbbell, whereas all three overreactors have substitutions in the C-terminal lobe. No mutations fell in the central helix connecting the two lobes. These results may indicate that the sites defined by these mutations are important in membrane excitation but not in other biological functions. They also suggest that the two lobes of calmodulin may be used differentially for the activation of different Ca2(+)-dependent channels.
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Affiliation(s)
- J A Kink
- Laboratory of Molecular Biology, University of Wisconsin, Madison 53706
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35
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George SE, VanBerkum MF, Ono T, Cook R, Hanley RM, Putkey JA, Means AR. Chimeric calmodulin-cardiac troponin C proteins differentially activate calmodulin target enzymes. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38836-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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36
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Nagao S, Matsuki S, Kanoh H, Ozawa T, Yamada K, Nozawa Y. Site-directed mutagenesis of glutamine residue of calmodulin. Activation of guanylate cyclase of Tetrahymena plasma membrane. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39266-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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37
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VanBerkum MF, George SE, Means AR. Calmodulin activation of target enzymes. Consequences of deletions in the central helix. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39658-9] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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38
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Babu A, Gulati J. Trifluoperazine inhibition of contraction in permeabilized skeletal, cardiac and smooth muscles. Biochem Biophys Res Commun 1990; 166:1421-8. [PMID: 2306255 DOI: 10.1016/0006-291x(90)91025-n] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
To gain insights into the mechanism of the central helix of calmodulin and troponin-C in the Ca2(+)-regulation of force development in striated and smooth muscles, the present study was made of the TFP induced inhibition of contraction, and of the uptake of these proteins by skinned fibers. Calmodulin was four-fold more sensitive to TFP than TnC, but the inhibition was found to be identical for skeletal and cardiac muscles despite the differences in their troponin-C isoforms. Also, the results were comparable between fast-twitch fiber, when calmodulin was exchanged for troponin-C to act on TnI, and smooth muscle, where calmodulin acts on myosin light chain kinase. These findings indicate that the inhibition of force by TFP is entirely due to its binding to the hydrophobic sites in the central helix. The uptakes of troponin-C and calmodulin were also different, and this is explained by a TFP-independent domain in troponin-C that binds TnI.
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Affiliation(s)
- A Babu
- Albert Einstein College of Medicine, Department of Medicine and Physiology/Biophysics, Bronx, NY 10461
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39
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You GF, Buccigross JM, Nelson DJ. Comparison of Ca(II), Cd(II), and Mg(II) titrations of tyrosine-99 spin-labeled bovine calmodulin. J Inorg Biochem 1990; 38:117-25. [PMID: 2157810 DOI: 10.1016/0162-0134(90)84020-p] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Bovine calmodulin, spin-labeled at tyrosine-99, has been utilized in electron paramagnetic resonance (EPR) studies to investigate calmodulin interactions with Ca(II), Cd(II), and Mg(II). The addition of either Ca(II) or Cd(II) to apo-calmodulin results in a complex capable of activating target enzymes, such as 3', 5'-cyclic nucleotide phosphodiesterase (J. M. Buccigross, C. L. O'Donnell, and D. J. Nelson, Biochem. J. 235 677 [1986]), while Mg(II) is known to be incapable of activating calmodulin toward any of its target enzymes. Additions of Ca(II) and Cd(II) to spin-labeled apo-calmodulin gave rise to very similar changes in the EPR spectrum of the bound label, consistent with a dramatic decrease in the mobility of the nitroxide spin-label covalently attached to tyrosine-99. Addition of Mg(II) to spin-labeled apo-calmodulin caused no change in the EPR spectrum of the bound label. Thus, the conformational changes induced by Ca(II) and Cd(II) ion binding to calmodulin, which lead to decreased tyrosine-99 spin label mobility, are clearly not occurring when Mg(II) ion binds. These results are consistent with the results of other spectroscopic studies, which indicate that "activating" metal ions, such as Ca(II) and Cd(II), produce calmodulin conformers that are different from those produced by "inactivating" metal ions, such as Mg(II).
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Affiliation(s)
- G F You
- Department of Chemistry, Clark University, Worcester, Massachusetts 01610
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40
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Haiech J, Kilhoffer MC, Craig TA, Lukas TJ, Wilson E, Guerra-Santos L, Watterson DM. Mutant analysis approaches to understanding calcium signal transduction through calmodulin and calmodulin regulated enzymes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1990; 269:43-56. [PMID: 2191562 DOI: 10.1007/978-1-4684-5754-4_7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
An example set of site-specific mutagenesis studies of calmodulin has been discussed in terms of strategy and how the results can provide insight into the functioning of calmodulin. A set of common examples for the study of calcium binding and enzyme activation were discussed. Essentially, site-specific mutagenesis in these initial studies is a perturbation approach. From these perturbation studies, structural features can be correlated in future studies with function and mechanisms of action proposed. More importantly, the approach allows efficient testing of proposed mechanisms and further probing of the molecular aspects of the signal transduction pathways. Clearly, the key functional feature that must be addressed in future studies is how the calcium binding steps in the mechanism are coupled to the enzyme activation step, which is the final step of the calmodulin-enzyme binding mechanism.
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41
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Abstract
Intramolecular distance measurements were made in cardiac troponin C (cTnC) by fluorescence energy transfer using Eu3+ or Tb3+ as energy donors and Nd3+ or an organic chromophore as acceptors. The laser-induced luminescence of bound Eu3+ is quenched in Eu1Nd1cTnC with a lifetime of 0.328 ms, compared with 0.43 ms for Eu2cTnC. The enhanced decay corresponds to an energy transfer efficiency of 0.25, or a distance of 1.1 nm between the two high affinity sites. We have also labeled cTnC with 4-dimethylaminophenylazophenyl-4'-maleimide (DAB-Mal) at the two cysteine residues (Cys-35 and Cys-84). Energy transfer measurements were carried out between Tb3+ bound to the high affinity sites and the labels attached to the domain containing the low affinity site. Upon uv irradiation at pH 6.7, Tb1cTnCDAB emits tyrosine-sensitized Tb3+ luminescence that decays bioexponentially with lifetimes of 1.29 and 0.76 ms. The shorter lifetime is ascribed to energy transfer from Tb3+ to the DAB labels, yielding an average distance of 3.4 nm between the donor and the acceptors. At pH 5.0, however, the luminescence decays exclusively with a single lifetime of 1.31 ms, suggesting that under these conditions all Tb3+ ions are more than 5.2 nm away from the label. Thus cTnC, like skeletal TnC, undergoes a pH-dependent conformational transition which converts an elongated structure at lower pH's to a rather compact conformation in a more physiological medium.
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Affiliation(s)
- C L Wang
- Department of Muscle Research, Boston Biomedical Research Institute, Massachusetts 02114
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42
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43
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Head JF. Amino acid sequence of a low molecular weight, high affinity calcium-binding protein from the optic lobe of the squid Loligo pealei. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)83221-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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44
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45
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Weber PC, Lukas TJ, Craig TA, Wilson E, King MM, Kwiatkowski AP, Watterson DM. Computational and site-specific mutagenesis analyses of the asymmetric charge distribution on calmodulin. Proteins 1989; 6:70-85. [PMID: 2558379 DOI: 10.1002/prot.340060107] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Calmodulin's calculated electrostatic potential surface is asymmetrically distributed about the molecule. Concentrations of uncompensated negative charge are localized near certain alpha-helices and calcium-binding loops. Further calculations suggest that these charge features of calmodulin can be selectively perturbed by changing clusters of phylogenetically conserved acidic amino acids in helices to lysines. When these cluster charge reversals are actually produced by using cassette-based site-specific mutagenesis of residues 82-84 or 118-120, the resulting proteins differ in their interaction with two distinct calmodulin-dependent protein kinases, myosin light chain kinase and calmodulin-dependent protein kinase II. Each calmodulin mutant can be purified to apparent chemical homogeneity by an identical purification protocol that is based on conservation of its overall properties, including calcium binding. Although cluster charge reversals result in localized perturbations of the computed negative surface, single amino acid changes would not be expected to alter significantly the distribution of the negative surface because of the relatively high density of uncompensated negative charge in the region around residues 82-84 and 118-120. However, this does not preclude the possibility of single amino acid charge perturbations having a functional effect on the more intimate, catalytically active complex. The electrostatic surface of calmodulin described in this report may be a feature that would be altered only by cluster charge reversal mutations. Overall, the results suggest that the charge properties of calmodulin are one of several properties that are important for the efficient assembly of calmodulin-protein kinase signal transduction complexes in eukaryotic cells.
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Affiliation(s)
- P C Weber
- Central Research and Development Department, E.I. du Pont de Nemours Co., Wilmington, Delaware 19880-0228
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46
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Hitchcock-DeGregori SE. Structure-function analysis of thin filament proteins expressed in Escherichia coli. CELL MOTILITY AND THE CYTOSKELETON 1989; 14:12-20. [PMID: 2684418 DOI: 10.1002/cm.970140105] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- S E Hitchcock-DeGregori
- Department of Anatomy, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854
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