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Mukherjea M, Ali MY, Kikuti C, Safer D, Yang Z, Sirkia H, Ropars V, Houdusse A, Warshaw DM, Sweeney HL. Myosin VI must dimerize and deploy its unusual lever arm in order to perform its cellular roles. Cell Rep 2014; 8:1522-32. [PMID: 25159143 DOI: 10.1016/j.celrep.2014.07.041] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Revised: 06/13/2014] [Accepted: 07/22/2014] [Indexed: 12/21/2022] Open
Abstract
It is unclear whether the reverse-direction myosin (myosin VI) functions as a monomer or dimer in cells and how it generates large movements on actin. We deleted a stable, single-α-helix (SAH) domain that has been proposed to function as part of a lever arm to amplify movements without impact on in vitro movement or in vivo functions. A myosin VI construct that used this SAH domain as part of its lever arm was able to take large steps in vitro but did not rescue in vivo functions. It was necessary for myosin VI to internally dimerize, triggering unfolding of a three-helix bundle and calmodulin binding in order to step normally in vitro and rescue endocytosis and Golgi morphology in myosin VI-null fibroblasts. A model for myosin VI emerges in which cargo binding triggers dimerization and unfolds the three-helix bundle to create a lever arm essential for in vivo functions.
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Affiliation(s)
- Monalisa Mukherjea
- Department of Physiology, University of Pennsylvania Perelman School of Medicine, 415 Curie Boulevard, 700 CRB, Philadelphia, PA 19104-6085, USA
| | - M Yusuf Ali
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA
| | - Carlos Kikuti
- Structural Motility, Centre de Recherche, Institut Curie, 75248 Paris, France; CNRS, UMR144, 26 rue d'Ulm, 75248 Paris Cedex 05, France
| | - Daniel Safer
- Department of Physiology, University of Pennsylvania Perelman School of Medicine, 415 Curie Boulevard, 700 CRB, Philadelphia, PA 19104-6085, USA
| | - Zhaohui Yang
- Department of Physiology, University of Pennsylvania Perelman School of Medicine, 415 Curie Boulevard, 700 CRB, Philadelphia, PA 19104-6085, USA
| | - Helena Sirkia
- Structural Motility, Centre de Recherche, Institut Curie, 75248 Paris, France; CNRS, UMR144, 26 rue d'Ulm, 75248 Paris Cedex 05, France
| | - Virginie Ropars
- Structural Motility, Centre de Recherche, Institut Curie, 75248 Paris, France; CNRS, UMR144, 26 rue d'Ulm, 75248 Paris Cedex 05, France
| | - Anne Houdusse
- Structural Motility, Centre de Recherche, Institut Curie, 75248 Paris, France; CNRS, UMR144, 26 rue d'Ulm, 75248 Paris Cedex 05, France
| | - David M Warshaw
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA
| | - H Lee Sweeney
- Department of Physiology, University of Pennsylvania Perelman School of Medicine, 415 Curie Boulevard, 700 CRB, Philadelphia, PA 19104-6085, USA.
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Guo H, Huang R, Semba S, Kordowska J, Huh YH, Khalina-Stackpole Y, Mabuchi K, Kitazawa T, Wang CLA. Ablation of smooth muscle caldesmon affects the relaxation kinetics of arterial muscle. Pflugers Arch 2012; 465:283-94. [PMID: 23149489 DOI: 10.1007/s00424-012-1178-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Revised: 10/26/2012] [Accepted: 10/30/2012] [Indexed: 01/04/2023]
Abstract
Smooth muscle caldesmon (h-CaD) is an actin- and myosin-binding protein that reversibly inhibits the actomyosin ATPase activity in vitro. To test the function of h-CaD in vivo, we eliminated its expression in mice. The h-CaD-null animals appeared normal and fertile, although the litter size was smaller. Tissues from the homozygotes lacked h-CaD and exhibited upregulation of the non-muscle isoform, l-CaD, in visceral, but not vascular tonic smooth muscles. While the Ca(2+) sensitivity of force generation of h-CaD-deficient smooth muscle remained largely unchanged, the kinetic behavior during relaxation in arteries was different. Both intact and permeabilized arterial smooth muscle tissues from the knockout animals relaxed more slowly than those of the wild type. Since this difference occurred after myosin dephosphorylation was complete, the kinetic effect most likely resulted from slower detachment of unphosphorylated crossbridges. Detailed analyses revealed that the apparently slower relaxation of h-CaD-null smooth muscle was due to an increase in the amplitude of a slower component of the biphasic tension decay. While the identity of this slower process has not been unequivocally determined, we propose it reflects a thin filament state that elicits fewer re-attached crossbridges. Our finding that h-CaD modulates the rate of smooth muscle relaxation clearly supports a role in the control of vascular tone.
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Affiliation(s)
- Hongqiu Guo
- Boston Biomedical Research Institute, Watertown, MA, 02472, USA
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3
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ABRAMS J, DAVULURI G, SEILER C, PACK M. Smooth muscle caldesmon modulates peristalsis in the wild type and non-innervated zebrafish intestine. Neurogastroenterol Motil 2012; 24:288-99. [PMID: 22316291 PMCID: PMC3919438 DOI: 10.1111/j.1365-2982.2011.01844.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
BACKGROUND The high molecular weight isoform of the actin-binding protein Caldesmon (h-CaD) regulates smooth muscle contractile function by modulating cross-bridge cycling of myosin heads. The normal inhibitory activity of h-CaD is regulated by the enteric nervous system; however, the role of h-CaD during intestinal peristalsis has never been studied. METHODS We identified a zebrafish paralog of the human CALD1 gene that encodes an h-CaD isoform expressed in intestinal smooth muscle. We examined the role of h-CaD during intestinal peristalsis in zebrafish larvae by knocking down the h-CaD protein using an antisense morpholino oligonucleotide. We also developed transgenic zebrafish that express inhibitory peptides derived from the h-CaD myosin and actin-binding domains, and examined their effect on peristalsis in wild-type zebrafish larvae and sox10 (colourless) mutant larvae that lack enteric nerves. KEY RESULTS Genomic analyses identified two zebrafish Caldesmon paralogs. The cald1a ortholog encoded a high molecular weight isoform generated by alternative splicing whose intestinal expression was restricted to smooth muscle. Propulsive intestinal peristalsis was increased in wild-type zebrafish larvae by h-CaD knockdown and by expression of transgenes encoding inhibitory myosin and actin-binding domain peptides. Peristalsis in the non-innervated intestine of sox10 (colourless) larvae was partially restored by h-CaD knockdown and expression of the myosin-binding peptide. CONCLUSIONS & INFERENCES Disruption of the normal inhibitory function of h-CaD enhances intestinal peristalsis in both wild-type zebrafish larvae and mutant larvae that lack enteric nerves, thus confirming a physiologic role for regulation of smooth muscle contraction at the actin filament.
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Affiliation(s)
- J. ABRAMS
- Department of Medicine, University of Pennsylvania School
of Medicine, Philadelphia, PA, USA
| | - G. DAVULURI
- Department of Medicine, University of Pennsylvania School
of Medicine, Philadelphia, PA, USA
| | - C. SEILER
- Department of Medicine, University of Pennsylvania School
of Medicine, Philadelphia, PA, USA
| | - M. PACK
- Department of Medicine, University of Pennsylvania School
of Medicine, Philadelphia, PA, USA,Department of Cell and Developmental Biology,
University of Pennsylvania School of Medicine, Philadelphia, PA, USA
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4
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Mayanagi T, Sobue K. Diversification of caldesmon-linked actin cytoskeleton in cell motility. Cell Adh Migr 2011; 5:150-9. [PMID: 21350330 DOI: 10.4161/cam.5.2.14398] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The actin cytoskeleton plays a key role in regulating cell motility. Caldesmon (CaD) is an actin-linked regulatory protein found in smooth muscle and non-muscle cells that is conserved among a variety of vertebrates. It binds and stabilizes actin filaments, as well as regulating actin-myosin interaction in a calcium (Ca2+)/calmodulin (CaM)- and/or phosphorylation-dependent manner. CaD function is regulated qualitatively by Ca2+/CaM and by its phosphorylation state and quantitatively at the mRNA level, by three different transcriptional regulation of the CALD1 gene. CaD has numerous functions in cell motility, such as migration, invasion, and proliferation, exerted via the reorganization of the actin cytoskeleton. Here we will outline recent findings regarding CaD's structural features and functions.
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Affiliation(s)
- Taira Mayanagi
- Department of Neuroscience, Osaka University Graduate School of Medicine, Osaka, Japan
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5
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Huang R, Grabarek Z, Wang CLA. Differential effects of caldesmon on the intermediate conformational states of polymerizing actin. J Biol Chem 2009; 285:71-9. [PMID: 19889635 DOI: 10.1074/jbc.m109.065078] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The actin-binding protein caldesmon (CaD) reversibly inhibits smooth muscle contraction. In non-muscle cells, a shorter CaD isoform co-exists with microfilaments in the stress fibers at the quiescent state, but the phosphorylated CaD is found at the leading edge of migrating cells where dynamic actin filament remodeling occurs. We have studied the effect of a C-terminal fragment of CaD (H32K) on the kinetics of the in vitro actin polymerization by monitoring the fluorescence of pyrene-labeled actin. Addition of H32K or its phosphorylated form either attenuated or accelerated the pyrene emission enhancement, depending on whether it was added at the early or the late phase of actin polymerization. However, the CaD fragment had no effect on the yield of sedimentable actin, nor did it affect the actin ATPase activity. Our findings can be explained by a model in which nascent actin filaments undergo a maturation process that involves at least two intermediate conformational states. If present at early stages of actin polymerization, CaD stabilizes one of the intermediate states and blocks the subsequent filament maturation. Addition of CaD at a later phase accelerates F-actin formation. The fact that CaD is capable of inhibiting actin filament maturation provides a novel function for CaD and suggests an active role in the dynamic reorganization of the actin cytoskeleton.
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Affiliation(s)
- Renjian Huang
- Boston Biomedical Research Institute, Watertown, Massachusetts 02472, USA
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6
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Chacko S, Chang S, Hypolite J, Disanto M, Wein A. Alteration of contractile and regulatory proteins following partial bladder outlet obstruction. ACTA ACUST UNITED AC 2009:26-36. [PMID: 15545194 DOI: 10.1080/03008880410015147] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
This paper reviews the contractility and the expression of contractile and regulatory proteins in the detrusor smooth muscle (DSM) following partial bladder outlet obstruction (PBOO) in rabbits. PBOO was surgically induced by partial ligation of the urethra in adult male New Zealand White rabbits. The force generated by DSM strips from normal and obstructed bladders which showed bladder dysfunction, despite detrusor hypertrophy (decompensated bladder, DB) was measured. The expression of contractile and regulatory proteins was analyzed by reverse transcriptase-polymerase chain reaction and Western blotting. The DSM from obstructed DB revealed an overexpression of SM-A myosin heavy chain isoform (associated with decreased maximum velocity of shortening). DSM from sham-operated rabbits showed phasic contractions, whereas the detrusor from DB was tonic, exhibiting slow development of force, a longer duration of force maintenance, and slow relaxation. Rho-kinase inhibitor Y-27632 enhanced the relaxation of precontracted (with 125 mM KCl) DSM strips from DB. The enhancement of relaxation of DB by Y-27632 was associated with dephosphorylation of myosin light chain. The detrusor from normal bladders expresses predominantly the smooth muscle caldesmon (h-CaD), a thin filament-associated protein. However, the DSM from DB shows an overexpression of l-CaD, the non-muscle isoform of CaD. The l-CaD colocalizes with myosin in the cytoplasmic filaments in myocytes. These results show that the alteration of contractility of the detrusor following PBOO is associated with changes in the expression of proteins that form the contractile apparatus and regulate the actomyosin ATPase activity and contraction.
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Affiliation(s)
- Samuel Chacko
- Department of Pathobiology, University of Pennsylvania, Philadelphia, 19104, USA.
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7
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Süveges D, Gáspári Z, Tóth G, Nyitray L. Charged single alpha-helix: a versatile protein structural motif. Proteins 2009; 74:905-16. [PMID: 18712826 DOI: 10.1002/prot.22183] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A few highly charged natural peptide sequences were recently suggested to form stable alpha-helical structures in water. In this article we show that these sequences represent a novel structural motif called "charged single alpha-helix" (CSAH). To obtain reliable candidate CSAH motifs, we developed two conceptually different computational methods capable of scanning large databases: SCAN4CSAH is based on sequence features characteristic for salt bridge stabilized single alpha-helices, whereas FT_CHARGE applies Fourier transformation to charges along sequences. Using the consensus of the two approaches, a remarkable number of proteins were found to contain putative CSAH domains. Recombinant fragments (50-60 residues) corresponding to selected hits obtained by both methods (myosin 6, Golgi resident protein GCP60, and M4K4 protein kinase) were produced and shown by circular dichroism spectroscopy to adopt largely alpha-helical structure in water. CSAH segments differ substantially both from coiled-coil and intrinsically disordered proteins, despite the fact that current prediction methods recognize them as either or both. Analysis of the proteins containing CSAH motif revealed possible functional roles of the corresponding segments. The suggested main functional features include the formation of relatively rigid spacer/connector segments between functional domains as in caldesmon, extension of the lever arm in myosin motors and mediation of transient interactions by promoting dimerization in a range of proteins.
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Affiliation(s)
- Dániel Süveges
- Department of Biochemistry, Eötvös Loránd University, Pázmány Péter s. 1/C, H1117 Budapest, Hungary
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8
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Wang CLA. Caldesmon and the regulation of cytoskeletal functions. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 644:250-72. [PMID: 19209827 DOI: 10.1007/978-0-387-85766-4_19] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Caldesmon (CaD) is an extraordinary actin-binding protein, because in addition to actin, it also bindsmyosin, calmodulin and tropomyosin. As a component of the smoothmuscle and nonmuscle contractile apparatus CaD inhibits the actomyosin ATPase activity and its inhibitory action is modulated by both Ca2+ and phosphorylation. The multiplicity of binding partners and diverse biochemical properties suggest CaD is a potent and versatile regulatory protein both in contractility and cell motility. However, after decades ofinvestigation in numerous laboratories, hard evidence is still lacking to unequivocally identify its in vivo functions, although indirect evidence is mounting to support an important role in connection with the actin cytoskeleton. This chapter reviews the highlights of the past findings and summarizes the current views on this protein, with emphasis of its interaction with tropomyosin.
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Affiliation(s)
- C L Albert Wang
- Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA.
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9
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Borovikov YS, Kulikova N, Pronina OE, Khaimina SS, Wrzosek A, Dabrowska R. Caldesmon freezes the structure of actin filaments during the actomyosin ATPase cycle. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2006; 1764:1054-62. [PMID: 16713410 DOI: 10.1016/j.bbapap.2006.04.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2005] [Revised: 03/27/2006] [Accepted: 04/03/2006] [Indexed: 11/27/2022]
Abstract
Hybrid contractile apparatus was reconstituted in skeletal muscle ghost fibers by incorporation of skeletal muscle myosin subfragment 1 (S1), smooth muscle tropomyosin and caldesmon. The spatial orientation of FITC-phalloidin-labeled actin and IAEDANS-labeled S1 during sequential steps of the acto-S1 ATPase cycle was studied by measurement of polarized fluorescence in the absence or presence of nucleotides conditioning the binding affinity of both proteins. In the fibers devoid of caldesmon addition of nucleotides evoked unidirectional synchronous changes in the orientation of the fluorescent probes attached to F-actin or S1. The results support the suggestion on the multistep rotation of the cross-bridge (myosin head and actin monomers) during the ATPase cycle. The maximal cross-bridge rotation by 7 degrees relative to the fiber axis and the increase in its rigidity by 30% were observed at transition between A**.M**.ADP.Pi (weak binding) and A--.M--.ADP (strong binding) states. When caldesmon was present in the fibers (OFF-state of the thin filament) the unidirectional changes in the orientation of actin monomers and S1 were uncoupled. The tilting of the myosin head and of the actin monomer decreased by 29% and 90%, respectively. It is suggested that in the "closed" position caldesmon "freezes" the actin filament structure and induces the transition of the intermediate state of actomyosin towards the weak-binding states, thereby inhibiting the ATPase activity of the actomyosin.
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Affiliation(s)
- Yurii S Borovikov
- Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, St. Petersburg 194064, Russia
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10
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Shepherd CM, van der Spoel D, Vogel HJ. Molecular dynamics simulations of peptides from the central domain of smooth muscle caldesmon. J Biomol Struct Dyn 2004; 21:555-66. [PMID: 14692799 DOI: 10.1080/07391102.2004.10506948] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
The central domain of smooth muscle caldesmon contains a highly charged region consisting of ten 13-residue repeats. Experimental evidence obtained from the intact protein and fragments thereof suggests that this entire region forms a single stretch of stable alpha-helix. We have carried out molecular dynamics simulations on peptides consisting of one, two and three repeats to examine the mechanism of alpha-helical stability of the central domain at the atomic level. All three peptides show high helical stability on the timescale of the MD simulations. Deviations from alpha-helical structure in all the simulations arise mainly from the formation of long stretches of pi-helix. Interconversion between alpha-helical and pi-helical conformations occurs through insertion of water molecules into alpha-helical hydrogen bonds and subsequent formation of reverse turns. The alpha-helical structure is stabilized by electrostatic interactions (salt bridges) between oppositely charged sidechains with i,i+4 spacings, while the pi-helix is stabilized by i,i+5 salt bridge interactions. Possible i,i+3 salt bridges are of minor importance. There is a strong preference for salt bridges with a Glu residue N-terminal to a basic sidechain as compared to the opposite orientation. In the double and triple repeat peptides, strong i,i+4 salt bridges exist between the last Glu residue of one repeat and the first Lys residue of the next. This demonstrates a relationship between the repetitive nature of the central domain sequence and its ability to form very long stretches of alpha-helical structure.
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Affiliation(s)
- Craig M Shepherd
- Department of Biological Sciences, Structural Biology Research Group, University of Calgary, 2500 University Dr NW, Calgary, Canada, T2N 1N4
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11
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Zhang EY, Stein R, Chang S, Zheng Y, Zderic SA, Wein AJ, Chacko S. Smooth muscle hypertrophy following partial bladder outlet obstruction is associated with overexpression of non-muscle caldesmon. THE AMERICAN JOURNAL OF PATHOLOGY 2004; 164:601-12. [PMID: 14742265 PMCID: PMC1602268 DOI: 10.1016/s0002-9440(10)63149-5] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Partial bladder outlet obstruction (PBOO) induces remodeling of urinary bladder smooth muscle (detrusor). We demonstrate an increase in bladder wall mass, muscle bundle size, and a threefold increase in the cross-sectional area of detrusor myocytes following PBOO in male New Zealand White rabbits compared to that of controls. Some bladders with detrusor hypertrophy function close to normal (compensated), whereas others were dysfunctional (decompensated), showing high intravesical pressure, large residual urine volume, and voiding difficulty. We analyzed the expression of smooth muscle-specific caldesmon (h-CaD) and non-muscle (l-CaD) by Western blotting, RT-PCR, and real-time PCR. The expression of l-CaD is increased significantly at the mRNA and protein levels in the decompensated bladders compared to that of normal and compensated bladders. The CaD was also co-localized with myosin containing cytoplasmic fibrils in cells dissociated from obstructed bladders and cultured overnight. Our data show that the inability of decompensated bladders to empty, despite detrusor hypertrophy, is associated with an overexpression of l-CaD. The level of l-CaD overexpression might be a useful marker to estimate the degree of detrusor remodeling and contractile dysfunction in PBOO.
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Affiliation(s)
- Erik Y Zhang
- Department of Pathobiology and Division of Urology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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12
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Krueger JK, Gallagher SC, Wang CA, Trewhella J. Calmodulin remains extended upon binding to smooth muscle caldesmon: a combined small-angle scattering and fourier transform infrared spectroscopy study. Biochemistry 2000; 39:3979-87. [PMID: 10747786 DOI: 10.1021/bi992638x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We show that calmodulin (CaM) has an extended conformation in its complexes with sequences from the smooth muscle thin filament protein caldesmon (CaD) by using small-angle X-ray and neutron scattering with contrast variation. The CaD sequences used in these experiments were a C-terminal fragment, 22kCaD, and a smaller peptide sequence within this fragment, MG56C. Each of these sequences contains the CaM-binding sites A and B previously shown to interact with the C- and N-terminal lobes of CaM, respectively [Wang et al. (1997) Biochemistry 36, 15026]. By modeling the scattering data, we show that the majority of the MG56C sequence binds to the N-terminal domain of CaM. FTIR data on CaM complexed with 22kCaD or with MG56C peptide show the 22kCaD sequence contains unordered, helix, and extended structures, and that the extended structures reside primarily in the MG56C portion of the sequence. There are small changes in secondary structure, involving approximately 12 residues, induced by CaM binding to CaD. These changes involve a net decrease in extended structures accompanied by an increase in alpha-helix, and they occur within the CaM and/or in the MG56C sequence.
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Affiliation(s)
- J K Krueger
- Bioscience Division, Mail Stop M888, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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13
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Hodgkinson JL. Actin and the smooth muscle regulatory proteins: a structural perspective. J Muscle Res Cell Motil 2000; 21:115-30. [PMID: 10961836 DOI: 10.1023/a:1005697301043] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The structural details of the smooth muscle acto-myosin interaction and its functional implications have been much discussed in recent years, however other, smooth muscle specific, actin-binding proteins have received much less attention. With increasing technical advances in structural biology a great deal of structural information is now coming to light, information that can provide useful insight into the mechanism of action for many important nonmotor actin-binding proteins. The purpose of the review is to instill the current knowledge on the structure, and interaction sites on F-actin, of the major, non-motor actin-binding proteins from smooth muscle, proposed to have a role in regulation. In the light of the recent structural studies the probable roles of the various actin-binding proteins will be discussed with particular reference to structure function relationships.
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Affiliation(s)
- J L Hodgkinson
- Imperial College of Science Technology and Medicine at The National Heart and Lung Institute, London, UK
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14
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Golitsina NL, Lehrer SS. Smooth muscle alpha-tropomyosin crosslinks to caldesmon, to actin and to myosin subfragment 1 on the muscle thin filament. FEBS Lett 1999; 463:146-50. [PMID: 10601656 DOI: 10.1016/s0014-5793(99)01589-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To obtain proximity information between tropomyosin (Tm) and caldesmon (CaD) on the muscle thin filament, we cloned gizzard alphaTm and created two single Cys mutants S56C/C190S (56Tm) and D100C/C190S (100Tm). They were labeled with benzophenone maleimide (BPM) and UV-irradiated on thin filaments. One chain of BPM-56Tm and two chains of BPM-100Tm crosslinked to CaD. Only BPM-100Tm crosslinked to actin in the absence and presence of CaD and binding of low ratios of myosin subfragment 1 (S1) prevented the crosslinking. Tm-S1 crosslinks were produced when actin.Tm was saturated with S1. Thus, CaD on the actin.Tm filament is located <10 A away from Tm amino acids 56 and 100; in the closed state of the actin.Tm filament, Tm residue 100 is located close to the actin surface and is moved further away in the S1-induced open state; in the open state, S1 binds close to Tm.
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Affiliation(s)
- N L Golitsina
- Muscle Research Group, Boston Biomedical Research Institute, Boston, MA 02115, USA
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15
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Abstract
The actin cytoskeleton is a dynamic filamentous network whose formation and remodeling underlies the fundamental processes of cell motility and shape determination. To serve these roles, different compartments of the actin cytoskeleton engage in forming specific coupling sites between neighbouring cells and with the underlying matrix, which themselves serve signal transducing functions. In this review, we focus on methods used to visualise the actin cytoskeleton and its dynamics, embracing the use of proteins tagged with conventional fluorophores and green fluorescent protein. Included also is a comparison of cooled CCD technology, confocal and 2-photon fluorescence microscopy of living and fixed cells, as well as a critique of current procedures for electron microscopy.
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Affiliation(s)
- J Small
- Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg, Austria.
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16
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Frisbie SM, Reedy MC, Yu LC, Brenner B, Chalovich JM, Kraft T. Sarcomeric binding pattern of exogenously added intact caldesmon and its C-terminal 20-kDa fragment in skinned fibers of skeletal muscle. J Muscle Res Cell Motil 1999; 20:291-303. [PMID: 10471992 DOI: 10.1023/a:1005490405222] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Intact caldesmon and particularly the actin-binding C-terminal fragment (20-kDa) of caldesmon have been shown in skeletal muscle fibers to selectively displace low affinity, weakly bound cross-bridges from actin without significantly altering the actin attachment of force producing, strong binding cross-bridges (Brenner et al., 1991; Kraft et al., 1995a). However, the sarcomeric distribution and the specific binding of externally added caldesmon to the myofilaments of skeletal muscle fibers was not known. It was e.g., unclear whether caldesmon binds along actin in a manner similar to tropomyosin or whether it also binds to myosin. In this study, we determined the binding pattern of exogenously added intact caldesmon and its C-terminal 20-kDa fragment, respectively, in MgATP-relaxed rabbit skeletal muscle fibers using electron (EM) and confocal fluorescence microscopy (CFM). EM showed that similar to what has been demonstrated earlier for smooth muscle thin filaments (Lehman et al., 1989), intact caldesmon binds periodically every 38 nm along the thin filaments. CFM revealed that rhodamine-labeled intact caldesmon and the 20-kDa caldesmon fragment bind along nearly the entire length of the thin filaments. A portion of the I-band near the Z-line appears unlabeled, both when equilibrated at normal and long sarcomere lengths. The width of the unlabeled region seems to depend on ionic strength. The 20-kDa C-terminal caldesmon fragment binds in essentially the same pattern as intact caldesmon. This indicates that the high fluorescence intensity in the overlap region seen with intact caldesmon does not depend on caldesmon binding to myosin. X-ray diffraction was used to monitor the effects of filament lattice. Intact caldesmon at > 0.3 mg/ml induced disorder in the myofilament lattice. No such disordering was observed, however, when fibers were equilibrated with up to 0.8 mg/ml of the 20-kDa caldesmon fragment.
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Affiliation(s)
- S M Frisbie
- National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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17
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Gunst SJ. Applicability of the sliding filament/crossbridge paradigm to smooth muscle. Rev Physiol Biochem Pharmacol 1999; 134:7-61. [PMID: 10087907 DOI: 10.1007/3-540-64753-8_2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Affiliation(s)
- S J Gunst
- Indiana University School of Medicine, USA
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18
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Marston S, Burton D, Copeland O, Fraser I, Gao Y, Hodgkinson J, Huber P, Levine B, el-Mezgueldi M, Notarianni G. Structural interactions between actin, tropomyosin, caldesmon and calcium binding protein and the regulation of smooth muscle thin filaments. ACTA PHYSIOLOGICA SCANDINAVICA 1998; 164:401-14. [PMID: 9887964 DOI: 10.1111/j.1365-201x.1998.tb10696.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The basic structure and functional properties of smooth muscle thin filaments were established about 10 years ago. Since then we and others have been working on the details of how tropomyosin, caldesmon and the Ca(2+)-binding protein regulate actin interaction with myosin. Our work has tended to emphasize the similarities between caldesmon and troponin function whilst others have been more concerned with the differences. The need to resolve the resulting differences has stimulated us to find new and more direct ways of investigating the mechanism of thin filament regulation. In recent years an apparent divergence has opened up between functional measurements, which indicate an allosteric-cooperative regulatory mechanism in which caldesmon and Ca(2+)-binding protein control actin-tropomyosin state in the same way as troponin, and structural measurements which show thin filament structures unlike striated muscle thin filaments. The challenge is to interpret function in terms of structure. We have combined functional studies with expression and mutagenesis of caldesmon and with structural methods including X-ray crystalography of tropomyosin-caldesmon crystals, electron microscopy and helical reconstruction of actin-tropomyosin-caldesmon complexes and high resolution nuclear magnetic resonance spectroscopy of the C-terminus of caldesmon in interaction with actin and calmodulin. We have used this information to propose a structural mechanism for caldesmon regulation of the smooth muscle thin filament.
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Affiliation(s)
- S Marston
- Imperial College School of Medicine, National Heart and Lung Institute, London, UK
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19
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Wang E, Zhuang S, Kordowska J, Grabarek Z, Wang CL. Calmodulin binds to caldesmon in an antiparallel manner. Biochemistry 1997; 36:15026-34. [PMID: 9398229 DOI: 10.1021/bi963075h] [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
Two of the five tryptophan residues (W659 and W692) in chicken gizzard smooth muscle caldesmon (CaD) are located within the calmodulin (CaM) binding sites in the C-terminal region of the molecule. When these Trp residues are replaced with Gly in either recombinant fragments or synthetic peptides of CaD, the affinity for CaM is decreased by at least 10-fold, suggesting that both of these residues are important for the interaction of CaD with CaM. To gain information about the topography of the CaM-CaD complex, we have carried out fluorescence titrations of CaM with Tb3+ as a substitute for Ca2+ in the presence of wild-type or mutated CaD variants. By exciting Trp residues of CaD fragments or peptides while monitoring the enhanced luminescence of CaM-bound Tb3+ ions via resonance energy transfer, we were able to estimate the relative proximity between the bound metal ions in the two domains of CaM and the Trp residues of CaD. Our results suggest that in the CaM-CaD complex the metal-binding sites III and IV in the C-terminal domain of CaM are very close to W659 of CaD; the N-terminal domain of CaM appears associated with the region of CaD in the vicinity of W692, although sites I and II are relatively far away from this Trp residue. These findings are consistent with a model in which CaM binds to CaD in an antiparallel manner. Such a binding mode, however, may be flexible enough to accommodate alternative spatial arrangements when the preferred binding sites are either altered or rendered unavailable.
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Affiliation(s)
- E Wang
- Muscle Research Group, Boston Biomedical Research Institute, Massachusetts 02114, USA
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20
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Makuch R, Zasada A, Mabuchi K, Krauze K, Wang CL, Dabrowska R. Phosphatidylserine liposomes can be tethered by caldesmon to actin filaments. Biophys J 1997; 73:1607-16. [PMID: 9284327 PMCID: PMC1181059 DOI: 10.1016/s0006-3495(97)78192-x] [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: 02/05/2023] Open
Abstract
Rotary shadowing electron microscopy revealed that attachment of caldesmon to phosphatidylserine (PS) liposomes was mainly through its C-terminal end. To determine the PS-binding sites of caldesmon, we have made use of synthetic peptides covering the two C-terminal calmodulin binding sites and a recombinant fragment corresponding to the N-terminal end of the C-terminal domain that contains an amphipathic helix. Interactions of these peptides with the PS liposomes were studied by nondenaturing gel electrophoresis and fluorescence spectroscopy. The results showed that both calmodulin-binding sites of caldesmon were able to interact with PS. The affinity (Kd) of PS for these sites was in the range of 1.8-14.3 x 10(-5) M, compared to 0.69 x 10(-5) M for the whole caldesmon molecule. Fragments located outside of calmodulin-binding sites bound PS weakly (3.85 x 10(-4) M) and thus may contain a second class of lipid-binding sites. Binding of PS induced conformational changes in regions other than the C-terminal PS-binding sites, as evidenced by the changes in the susceptibility to proteolytic cleavages. Most significantly, the presence of caldesmon greatly increased binding of PS to F-actin, suggesting that caldesmon may tether PS liposomes to actin filaments. These results raise the possibility that caldesmon-lipid interactions could play a functionally important role in the assembly of contractile filaments near the membranes.
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Affiliation(s)
- R Makuch
- Department of Muscle Biochemistry, Nencki Institute of Experimental Biology, Warsaw, Poland
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21
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Graceffa P. Arrangement of the COOH-terminal and NH2-terminal domains of caldesmon bound to actin. Biochemistry 1997; 36:3792-801. [PMID: 9092808 DOI: 10.1021/bi961652w] [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: 02/04/2023]
Abstract
Smooth muscle caldesmon is a single polypeptide chain with its NH2- and COOH-terminal domains separated by a long alpha-helix. Caldesmon was labeled at either Cys-153 in the NH2 domain or Cys-580 in the COOH domain with a variety of fluorescence probes. Fluorescence intensity, peak position, and polarization of probes on Cys-580 were very sensitive to the binding to actin (with or without tropomyosin), whereas for probes on Cys-153, there was a lack of response, in reconstituted or native actin thin filaments. From fluorescence resonance energy transfer from donor labels on either caldesmon cysteine to acceptor labels on Cys-374 of actin, the distance between the donor and acceptor was estimated to be 27 A for the donor at Cys-580 and 65-80 A for the donor at Cys-153. These findings were the same for caldesmon prepared with or without heat treatment and with striated or smooth muscle actin. These results, together with previous knowledge that COOH-terminal fragments of caldesmon bind to actin whereas NH2-terminal fragments do not, indicate that, while the COOH domain of caldesmon is bound to actin, the NH2 domain is largely dissociated. Fluorescence quenching studies showed that actin binding to caldesmon greatly decreased the accessibility of probes at caldesmon Cys-580 to the quencher, whereas for probes at Cys-153, actin afforded much less, but significant, protection from quenching. Consequently, it appears that, although the NH2 domain is mostly dissociated, it spends some time in the vicinity of actin, through either a weak interaction with actin or collisions with actin and/or because of restricted flexibility which constrains the NH2 domain to be close to the actin filament. Since the NH2 domain of caldesmon binds to the neck region of myosin, a dissociated NH2 domain may account for caldesmon's ability to link myosin and actin filaments.
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Affiliation(s)
- P Graceffa
- Muscle Research Group, Boston Biomedical Research Institute, Massachusetts 02114, USA.
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22
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Czuryło EA, Hellweg T, Eimer W, Dabrowska R. The size and shape of caldesmon and its fragments in solution studied by dynamic light scattering and hydrodynamic model calculations. Biophys J 1997; 72:835-42. [PMID: 9017208 PMCID: PMC1185606 DOI: 10.1016/s0006-3495(97)78717-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The size and the shape of caldesmon as well as its 50-kDa central and 19-kDa C-terminal fragments were investigated by photon correlation spectroscopy. The hydrodynamic radii, which have been calculated from the experimentally obtained translational diffusion coefficients, are 9.8 nm, 6.0 nm, and 2.9 nm, respectively. Moreover, the experimental values for the translational diffusion coefficients are compared with results obtained from hydrodynamic model calculations. Detailed models for the structure of caldesmon in solution are derived. The contour length is about 64 nm for all of the models used for caldesmon.
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Affiliation(s)
- E A Czuryło
- Department of Muscle Biochemistry, Nencki Institute of Experimental Biology, Warsaw, Poland
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23
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Hnath EJ, Wang CL, Huber PA, Marston SB, Phillips GN. Affinity and structure of complexes of tropomyosin and caldesmon domains. Biophys J 1996; 71:1920-33. [PMID: 8889167 PMCID: PMC1233659 DOI: 10.1016/s0006-3495(96)79391-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The interaction of caldesmon domains with tropomyosin has been studied using x-ray crystallography and an optical biosensor. Only whole caldesmon and the carboxyl-terminal domain of caldesmon (CaD-4, chicken gizzard residues 597-756) bound to tropomyosin with greater than millimolar affinity at 100 and 150 microM salt. Under these conditions the affinities of whole caldesmon and CaD-4 were both in the micromolar range. Data from the x-ray studies showed that whole caldesmon bound to tropomyosin in several places, with the region of tightest interaction being at tropomyosin residues 70-100 and/or 230-260. Studies with CaD-4 revealed that this region corresponded to the strong binding site seen with whole caldesmon. Weaker association of other regions of caldesmon to tropomyosin residues 180-210 and 5-50 was also observed. The results suggest that the carboxyl-terminus of caldesmon binds tightly to tropomyosin and that other regions of caldesmon may interact with tropomyosin tightly only when they are held close to tropomyosin by the carboxyl-terminal domain. Four models are presented to show the possible interactions of caldesmon with tropomyosin.
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Affiliation(s)
- E J Hnath
- Department of Biochemistry and Cell Biology, W.M. Keck Center for Computational Biology, Rice University, Houston, Texas 77005, USA
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24
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Mabuchi K, Li Y, Tao T, Wang CL. Immunocytochemical localization of caldesmon and calponin in chicken gizzard smooth muscle. J Muscle Res Cell Motil 1996; 17:243-60. [PMID: 8793726 DOI: 10.1007/bf00124246] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The distribution of caldesmon and calponin in chicken gizzard smooth muscle was investigated with immunofluorescence and immunogold electron microscopy. Immunofluorescence microscopy showed that in verapamil treated (relaxed) muscles the distributions of caldesmon and myosin appeared to be uniform throughout the cytoplasm, but clearly more textured than that of actin filaments as revealed by the distribution of tropomyosin. In shortened muscles both caldesmon and myosin became segregated, in contrast to the distribution of actin, which remained uniform. The distribution of calponin was even more textured, with no similarity to those of caldesmon or myosin. Instead, considerable overlap was observed between calponin and the cytoskeletal protein desmin and, to a lesser extent, beta-actin. By immunogold electron microscopy caldesmon appeared mostly near and around myosin filaments in both relaxed and shortened muscle. Calponin, on the other hand, was found primarily at the periphery of cytoskeletal structures in the same general region as desmin, and very often adjacent to beta-actin, which is mainly in the core. These observations indicated that caldesmon and calponin are associated with different subsets of actin filaments, caldesmon with contractile actin, while calponin with cytoskeletal actin. Thus the in situ localization of caldesmon is consistent with its proposed regulatory function. Calponin, on the other hand, is unlikely to directly regulate actomyosin interactions in these cells; instead, it may function as a bridging protein between the actin and the intermediate filament networks.
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Affiliation(s)
- K Mabuchi
- Muscle Research Group, Boston Biomedical Research Institute, MA 02114, USA
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25
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Crosbie RH, Chalovich JM, Reisler E. Flexation of caldesmon: effect of conformation on the properties of caldesmon. J Muscle Res Cell Motil 1995; 16:509-18. [PMID: 8567938 DOI: 10.1007/bf00126435] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The contribution of the extended and bent forms of caldesmon to its function was investigated by examining chemically modified forms of this protein. The bent 'hairpin' form of caldesmon was enhanced between pH 6.0 and 8.0 and at low ionic strengths, as reported by an increase in excimer fluorescence of pyrene-labelled caldesmon under these conditions. The presence of nucleotides also produced significant conformational changes in caldesmon, as detected by fluorescence measurements and protease digestions. Titrations of pyrene caldesmon with actin, heavy meromyosin, and calmodulin resulted in a decrease in excimer fluorescence. The function of the bent form of caldesmon was investigated by using intramolecular 1-ethyl-3-(3-dimethylamino propyl) carbodiimide-crosslinked caldesmon. The inhibition of acto-S-1 ATPase activity by crosslinked caldesmon was less efficient compared with that by pyrene modified and control caldesmons. Caldesmon's ability to switch from an activator to an inhibitor of actin-activated ATPase of myosin was also affected by the folding. Cosedimentation experiments revealed normal binding of crosslinked caldesmon to smooth muscle myosin. These results indicate the importance of caldesmon's transition from extended to folded forms and suggest possible functional roles for these different forms of caldesmon.
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Affiliation(s)
- R H Crosbie
- Department of Chemistry and Biochemistry, University of California, Los Angeles 90024, USA
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26
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Abstract
Smooth muscle cells have developed a contractile machinery that allows them to exert tension on the surrounding extracellular matrix over their entire length. This has been achieved by coupling obliquely organized contractile filaments to a more-or-less longitudinal framework of cytoskeletal elements. Earlier structural data suggested that the cytoskeleton was composed primarily of intermediate filaments and played only a passive role. More recent findings highlight the segregation of actin isotypes and of actin-associated proteins between the contractile and cytoskeletal domains and raise the possibility that the cytoskeleton performs a more active function. Current efforts focus on defining the relative contributions of myosin cross-bridge cycling and actin-associated protein interactions to the maintenance of tension in smooth muscle tissue.
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Affiliation(s)
- J V Small
- Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg, Austria
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27
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Zhuang S, Wang E, Wang CL. Identification of the functionally relevant calmodulin binding site in smooth muscle caldesmon. J Biol Chem 1995; 270:19964-8. [PMID: 7650012 DOI: 10.1074/jbc.270.34.19964] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The C-terminal region of smooth muscle caldesmon (CaD) interacts with calmodulin (CaM) and reverses CaD's inhibitory effect on the actomyosin ATPase activity. We have previously shown that the major CaM-binding site (site A) in this region is within the segment from Met-658 to Ser-666 (Zhan, Q., Wong, S. S., and Wang, C.-L. A. (1991) J. Biol. Chem. 266, 21810-21814). Recently, another segment (site B), Asn-675 to Lys-695, was reported to bind CaM (Mezgueldi, M., Derancourt, J., Calas, B., Kassab, R., and Fattoum, A. (1994) J. Biol. Chem. 269, 12824-12832). To assess the functional relevance of these two putative CaM-binding sites, we have examined three synthetic peptides regarding their effects on CaM's ability to reverse CaD-induced inhibition of actomyosin ATPase activity: GS17C (Gly-651 to Ser-667), VG29C (Val-685 to Gly-713), each containing one CaM-binding site, and MG56C (Met-658 to Gly-713), which contains both sites. We found that although VG29C did bind CaM, its affinity was weakened by GS17C, and it failed to compete with CaD for CaM under the conditions where GS17C effectively displaced CaD from CaM. MG56C had an effect similar to that of GS17C. These experiments demonstrated that site A for CaM binding is involved in regulating the inhibitory property of CaD.
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Affiliation(s)
- S Zhuang
- Muscle Research Group, Boston Biomedical Research Institute, Massachusetts 02114, USA
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28
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Katayama E, Ikebe M. Mode of caldesmon binding to smooth muscle thin filament: possible projection of the amino-terminal of caldesmon from native thin filament. Biophys J 1995; 68:2419-28. [PMID: 7647246 PMCID: PMC1282152 DOI: 10.1016/s0006-3495(95)80424-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The structure of smooth muscle thin filament was examined by various electron microscopy techniques, with special attention to the mode of caldesmon binding. Chemical cross-linking was positively used to avoid the dissociation of accessory proteins upon dilution. Caldesmon in reconstituted thin filament was observed as fine filamentous projections from thin filament. Native thin filament isolated from smooth muscle showed similarly numerous fine whisker-like projections by all the techniques employed here. Antibody against the amino-terminus of caldesmon labeled the end of such projections indicating the possibility that the amino-terminal myosin binding moiety might stick out from the shaft of the thin filament. Such whiskers are often projected out as a cluster to the same side of native thin filament. Further, we could visualize the assembly of dephosphorylated heavy meromyosin (HMM) with native or reconstituted thin filament forming "nonproductive" complex in the presence of ATP. The association of HMM to the shaft of thin filament was through subfragment-2 moiety, in accordance with biochemical studies. Some HMM particles bound closer to the thin filament shaft, possibly suggesting the presence of the second myosin-binding site on caldesmon. Occasionally two kinds of HMM association as such coexisted at a single site on this filament in tandem. Thus, we constructed a structural model of thin filament. The proposed molecular arrangement is not only compatible with all the biochemical results but also provides additional support for our recent findings (E. Katayoma, G. C. Scott-Woo, and M. Ikebe (1995) J. Biol. Chem. 270, 3919-3925) regarding the capability of caldesmon to induce dephosphorylated myosin filament, which explains the existence of thick filaments in relaxed smooth muscle cells.
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Affiliation(s)
- E Katayama
- Department of Fine Morphology, University of Tokyo, Japan
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29
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Payne AM, Yue P, Pritchard K, Marston SB. Caldesmon mRNA splicing and isoform expression in mammalian smooth-muscle and non-muscle tissues. Biochem J 1995; 305 ( Pt 2):445-50. [PMID: 7832758 PMCID: PMC1136382 DOI: 10.1042/bj3050445] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The recent determination of the genomic sequence of human caldesmon indicates that eight caldesmon mRNA species could be generated by selection of exon 1 or 1', exon 3a or 3ab and/or exon 4. We used reverse transcriptase PCR to determine which transcripts were produced in human, rabbit and sheep artery, vein, lung, intestine, kidney and liver. In all tissues the same three transcripts were present: exons 1'-2-3a-5-6...13, exons 1'-2-3a3b-5-6-...13 and exons 1'-2-3a3b-4-5-6...13. Exon 1 was not present and exon 4 was only present when exon 3b was also present. Three protein isoforms of caldesmon can be distinguished by electrophoresis on high-porosity 6% polyacrylamide gel: 130 kDa, 120 kDa and 70 kDa. The 70 kDa isoform lacks the sequence encoded by exon 3b. We investigated whether the two high-molecular-mass isoforms correspond to the presence and absence of exon 4 using an antiserum specific to the sequence encoded by exon 4. Western-blotting and immunoprecipitation experiments showed that both the 130 kDa and the 120 kDa isoforms were expressed with and without the exon 4 sequence. We therefore propose that the molecular-mass heterogeneity arises from additional first exons, possibly with separate promoter regions, which have not yet been characterized in the genomic sequence.
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Affiliation(s)
- A M Payne
- Department of Cardiac Medicine, National Heart and Lung Institute, London, U.K
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30
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Bogatcheva NV, Panaiotov MP, Vorotnikov AV, Gusev NB. Effect of 67 kDa calcimedin on caldesmon functioning. FEBS Lett 1993; 335:193-7. [PMID: 8253195 DOI: 10.1016/0014-5793(93)80728-d] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Interaction of smooth muscle caldesmon with calmodulin, troponin C, S-100 protein and 67 kDa calcimedin was analyzed. Native gel electrophoresis and crosslinking revealed the complex formation between caldesmon and three EF-hand Ca-binding proteins, whereas calcimedin did not interact with caldesmon. In the presence of Ca2+, calcimedin binds to actin-tropomyosin without affecting the interaction of caldesmon with this complex. Although calcimedin reversed the inhibitory action of caldesmon on the actomyosin ATPase activity at a lower concentration than three other Ca-binding proteins, this effect only slightly depends on Ca2+ and was observed at the concentration of calcimedin comparable to that of actin. It is concluded that calcimedin itself cannot be responsible for Ca-dependent regulation of caldesmon functioning, but actin bundling induced by calcimedin (or by other actin binding proteins) decreases the inhibitory action of caldesmon on the actomyosin ATPase activity.
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Affiliation(s)
- N V Bogatcheva
- Department of Biochemistry, School of Biology, Moscow State University, Russian Federation
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31
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Vibert P, Craig R, Lehman W. Three-dimensional reconstruction of caldesmon-containing smooth muscle thin filaments. J Cell Biol 1993; 123:313-21. [PMID: 8408215 PMCID: PMC2119844 DOI: 10.1083/jcb.123.2.313] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Caldesmon is known to inhibit actomyosin ATPase and filament sliding in vitro, and may play a role in modulating smooth muscle contraction as well as in diverse cellular processes including cytokinesis and exocytosis. However, the structural basis of caldesmon action has not previously been apparent. We have recorded electron microscope images of negatively stained thin filaments containing caldesmon and tropomyosin which were isolated from chicken gizzard smooth muscle in EGTA. Three-dimensional helical reconstructions of these filaments show actin monomers whose bilobed shape and connectivity are very similar to those previously seen in reconstructions of frozen-hydrated skeletal muscle thin filaments. In addition, a continuous thin strand of density follows the long-pitch actin helices, in contact with the inner domain of each actin monomer. Gizzard thin filaments treated with Ca2+/calmodulin, which dissociated caldesmon but not tropomyosin, have also been reconstructed. Under these conditions, reconstructions also reveal a bilobed actin monomer, as well as a continuous surface strand that appears to have moved to a position closer to the outer domain of actin. The strands seen in both EGTA- and Ca2+/calmodulin-treated filaments thus presumably represent tropomyosin. It appears that caldesmon can fix tropomyosin in a particular position on actin in the absence of calcium. An influence of caldesmon on tropomyosin position might, in principle, account for caldesmon's ability to modulate actomyosin interaction in both smooth muscles and non-muscle cells.
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Affiliation(s)
- P Vibert
- Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254
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32
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Czuryło EA, Dabrowska R. Studies on secondary structure of caldesmon and its C-terminal fragments. Biochem J 1993; 293 ( Pt 2):363-8. [PMID: 8343116 PMCID: PMC1134368 DOI: 10.1042/bj2930363] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Evaluation of the secondary structure of caldesmon from c.d. spectra revealed that it contains 51% helix, 9% beta-strand and 40% of remainder structures. These values agree well with the predicted ones from amino acid sequence, assuming an extended chain structure for caldesmon. The estimates of the secondary-structure elements in C-terminal 34 kDa and 19 kDa fragments are: 11 and 12% helix, 22 and 20% beta-strand, 13 and 17% beta-turns and loops, and 54 and 50% of remainder structure respectively. The best fit of experimental data was obtained assuming the globular state of the fragments. On the basis of structural analysis and fragmentation by proteolytic and chemical cleavages the six-domain model of caldesmon is proposed.
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Affiliation(s)
- E A Czuryło
- Nencki Institute of Experimental Biology, Department of Muscle Biochemistry, Warszawa, Poland
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33
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Mabuchi K, Lin JJ, Wang CL. Electron microscopic images suggest both ends of caldesmon interact with actin filaments. J Muscle Res Cell Motil 1993; 14:54-64. [PMID: 8478429 DOI: 10.1007/bf00132180] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
An improved rotary shadowing technique enabled us to visualize chicken gizzard caldesmon (CaD) and its complexes with one or two covalently linked calmodulin (CaM) molecules by electron microscopy. Using a monoclonal antibody against an epitope in the N-terminal region of CaD (anti-N), we can now identify the end of the molecule that is involved in binding to another protein molecule. Thus in the 1:1 complex of CaD and CaM, the CaM molecule was almost always associated with the C-terminus of CaD, indicating preferential CaM-binding to the C-terminal region. We have also studied binding of CaD to filamentous actin (F-actin), using an EM technique that avoids spraying or freeze drying and thereby preserves the structure of F-actin. Only one end of CaD appeared to bind to F-actin, leaving the rest of the molecule projecting away from the filament. While the majority of anti-N bound at the free end of CaD, some antibody molecules were found on F-actin. These findings suggest that either end of CaD can bind to F-actin. Experiments using a monoclonal antibody against the C-terminus of CaD (anti-C) supported this idea. When the native thin filaments that contain endogenous CaD were incubated with anti-N, almost all the bound antibodies were found on the filaments, indicating that the N-terminal regions of CaD interact with actin, and that the binding affinity of the N-terminal region of CaD for actin is higher in vivo than that in vitro, either because the properties of CaD have been altered during purification, or because of the presence of some other component(s) associated with the native filaments.
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Affiliation(s)
- K Mabuchi
- Department of Muscle Research, Boston Biomedical Research Institute, MA 02114
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34
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35
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Graceffa P, Jancsó A, Mabuchi K. Modification of acidic residues normalizes sodium dodecyl sulfate-polyacrylamide gel electrophoresis of caldesmon and other proteins that migrate anomalously. Arch Biochem Biophys 1992; 297:46-51. [PMID: 1637182 DOI: 10.1016/0003-9861(92)90639-e] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Caldesmon migrates as a 140-kDa protein during polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS), although its true molecular mass is close to 90 kDa. Since caldesmon's high acidic residue content may be responsible for this anomaly, it was reasoned that modification of these residues, with a loss of negative charge, might restore normal electrophoretic migration. Therefore caldesmon was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide in the presence of excess ethanolamine, which results in negatively charged carboxylates being converted to neutral amides without protein cross-linking. The absence of cross-linking was shown by rotary shadow electron microscopy. In accord with expectations, modified caldesmon migrated as a 94-kDa protein when compared to standards, which were much less affected by modification. The anomalous migration of caldesmon might be due to the repulsion of negatively charged SDS by caldesmon's acidic residues. Low binding of SDS to caldesmon is consistent with the fact that SDS, up to 1%, had little or no effect on the secondary structure of caldesmon, as monitored by circular dichroism. However, other mechanisms can also explain these observations. The abnormal migration of tropomyosin and calsequestrin, both of which have a high percentage of acidic amino acids, was also "normalized" by this treatment. Thus this method might have general application for the electrophoresis of proteins which have a high acidic residue content and migrate anomalously.
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Affiliation(s)
- P Graceffa
- Department of Muscle Research, Boston Biomedical Research Institute, Massachusetts 02114
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Chalovich J, Bryan J, Benson C, Velaz L. Localization and characterization of a 7.3-kDa region of caldesmon which reversibly inhibits actomyosin ATPase activity. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42051-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Abstract
Caldesmon (CDM) is a potential actomyosin regulatory protein found in smooth muscle and nonmuscle cells. Domain mapping and physical studies suggest that CDM is an elongated molecule with an N-terminal myosin/calmodulin-binding domain and a C-terminal tropomyosin/actin/calmodulin-binding domain separated by a 40-nm-long central helix. An 1100-nucleotide (nt) cDNA probe encoding the C terminus of avian caldesmon (aCDM) was used to screen a human aorta library and clone smooth-muscle and non-muscle CDM-encoding cDNAs (CDM). The human (h) smooth-muscle hCDM is 3050-3630 nt long, having variation in length in the 3'-untranslated region. The predicted hCDM protein has a high degree of identity, greater than 90%, to aCDM in the N- and C-terminal-binding domains. The central helical domain is more variable, but retains characteristic repeated peptides and an 'i, i + 4' acidic/basic amino acid (aa) motif found in aCDM which can form intra-helical salt bridges to stabilize the central helix. The predicted smooth-muscle protein is 793 aa long (93,262 Da) with a calculated pI of 5.75. As is the case for the chicken, nonmuscle hCDM is missing the central helical domain, 256 aa overall. Our nonmuscle clone is not full length, but the C-terminal end is identical to the smooth-muscle form. If the N-terminal domain is identical, as it is in the chicken, the predicted protein is 537 aa (62,558 Da). Examination of the 'junctions' at either end of the deleted central domain gives a clear indication of the splice sites and suggests that the nonmuscle form is generated by exon skipping.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M B Humphrey
- Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030
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Affiliation(s)
- S B Marston
- Department of Cardiac Medicine, National Heart and Lung Institute, London, UK
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Abstract
We have sequenced a cloned cDNA from a chicken gizzard library which encodes a short version of caldesmon with the properties expected for the non-muscle protein. The predicted protein is 524 amino acids long with a molecular mass of 60,174 daltons. Expression in bacteria produces a protein with an apparent molecular weight on SDS gels of 75-77,000, that comigrates with human platelet caldesmon. The expressed protein binds to F-actin and is retained on calmodulin-Sepharose in the presence, but not absence of Ca2+. This non-muscle caldesmon isoform is identical to the smooth muscle protein at the N- and C-terminal ends, but is missing 232 amino acids from the centre. This central segment is thought to be helical, suggesting that non-muscle caldesmon is approximately 35 nm shorter, about 40 nm overall length, than smooth muscle caldesmon.
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Affiliation(s)
- J Bryan
- Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030
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