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Katoh T, Morita F. The effect of cross-linking of the two heads of porcine aorta smooth muscle myosin on its conformation and enzymic activity. EUROPEAN JOURNAL OF BIOCHEMISTRY 1995; 233:123-31. [PMID: 7588735 DOI: 10.1111/j.1432-1033.1995.123_1.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The two heads of porcine aorta smooth muscle myosin can be cross-linked by a disulfide bridge between the two 17-kDa essential light chains with 5,5'-dithiobis(2-nitrobenzoic acid) [Katoh, T., Tanahashi, K., Hasegawa, Y. & Morita, F. (1995) Eur. J. Biochem. 227, 459-465]. When the cross-linked myosin sample was visualized by rotary shadowing, the two heads of myosin molecules appeared predominantly to adhere to each other. The cross-linking of dephosphorylated myosin in the presence of ATP was greatly inhibited by a decrease in the concentration of NaCl from 0.4 M to 0.15 M, suggesting that the cross-linking of the two heads was suppressed in 10S myosin. However, the fraction of dephosphorylated myosin in a filamentous state at 0.1 M NaCl in the presence of 1 mM ATP was increased from 33% to 83% by the cross-linking. The cross-linking of the two heads might inhibit the formation of the 10S conformation, leading to the increase in the fraction of filamentous myosin. The filaments of the cross-linked myosin sample were visualized by electron microscopy and appeared morphologically similar to those of uncross-linked myosin. The ATPase activity of the cross-linked dephosphorylated myosin sample was more than three times as high as that of an uncross-linked control. The increase in the activity may be related to the increase in the fraction of filamentous myosin caused by the cross-linking. The ATPase activity of dephosphorylated myosin in the presence of actin was increased more than twofold by the cross-linking, but the activity of phosphorylated myosin was affected only slightly. The degree of phosphorylation-dependent regulation of actin-activated ATPase activity decreased with an increase in the degree of cross-linking and was extrapolated to zero at 100% cross-linking. Superprecipitation of acto-cross-linked dephosphorylated myosin was activated, while that of acto-cross-linked phosphorylated myosin was inhibited only slightly. These results suggest that the freedom of each head in myosin molecules may be required to keep the ATPase activity and superprecipitation of acto-dephosphorylated myosin low but not for keeping these activity levels high in acto-phosphorylated myosin.
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Affiliation(s)
- T Katoh
- Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, Japan
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52
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Lowey S, Trybus KM. Role of skeletal and smooth muscle myosin light chains. Biophys J 1995; 68:120S-126S; discussion 126S-127S. [PMID: 7787054 PMCID: PMC1281891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
A persistent problem with the rotating cross-bridge model for muscle contraction has been the inability to detect any large conformational changes within the myosin molecule to account for a working stroke of 5-10 nm. The recent crystal structure of myosin subfragment-1 suggests a solution to this problem by showing the presence of two distinct domains: a catalytic or motor domain, from which extends a long, 8.5-nm alpha-helix that is stabilized by the regulatory and essential light chains. Rayment et al. (1993) proposed that closure of a cleft in the motor domain could rotate the light chain-binding domain by a sufficient distance to account for the power stroke. With the development of new in vitro motility assays, and the ability to prepare unusual myosins by biochemical and molecular biological methods, we can now examine this hypothesis and explore the role of the light chains in generating force and movement. Here we will review some of these recent data and outline a possible mechanism for how light chains regulate contractile properties.
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Affiliation(s)
- S Lowey
- Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254-9110, USA
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53
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Cremo CR, Sellers JR, Facemyer KC. Two heads are required for phosphorylation-dependent regulation of smooth muscle myosin. J Biol Chem 1995; 270:2171-5. [PMID: 7836446 DOI: 10.1074/jbc.270.5.2171] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Recent structural evidence (Rayment, I., Holden, H. M., Whittaker, M., Yohn, C. B., Lorenz, M., Holmes, K. C., and Milligan, R. A. (1993) Science 261, 58-65) suggests that the two heads of skeletal muscle myosin interact when the protein is bound to filamentous actin. Direct chemical cross-linking experiments show that the two heads of smooth muscle myosin interact in the presence of filamentous actin and the absence of ATP (Onishi, H., Maita, T., Matsuda, G., and Fujiwara, K. (1992) Biochemistry 31, 1201-1210). Head-head interactions may be important in the mechanism of phosphorylation-dependent regulation of smooth muscle myosin. To explore the structural elements essential for phosphorylation-dependent regulation, we purified a proteolytic fragment of chicken gizzard myosin containing only one head attached to an intact tail. This molecule contained a partially digested regulatory light chain, which was replaced with exogenously added intact light chain in either the thiophosphorylated or the unphosphorylated state. Control experiments showed that this replacement was nearly quantitative and did not alter the actin-activated ATPase of this myosin. Electron micrographs confirmed that the single-headed preparation contained an intact form of single-headed myosin. The unphosphorylated single-headed myosin hydrolyzed ATP rapidly and moved actin filaments in an in vitro motility assay. Phosphorylation had minimal effects upon these properties. Therefore, we conclude that phosphorylation-dependent regulation in this myosin requires two heads. These findings may have important implications in studies of other regulated motor proteins that contain two motor domains.
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Affiliation(s)
- C R Cremo
- Department of Biochemistry and Biophysics, Washington State University, Pullman 99164-4660
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54
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Abstract
In summary, phosphorylation of the regulatory light chain of myosin by Ca2+/CaM-dependent MLCK plays an important role in smooth muscle contraction. Although there have been major advances in our understanding of the regulation and physiological functions of contractile proteins in smooth muscle in recent years, very little information exists on the functional status of these proteins in human myometrium during pregnancy. The simple view that contractile force in smooth muscle is proportionate to cytoplasmic Ca2+ concentrations (Ca2+i) and myosin light chain phosphorylation is now more complex as more experiments provide insights into mechanisms of regulation of the contractile elements. MLCK can be phosphorylated, which desensitizes its activation by Ca2+/CaM, and protein phosphatase activity toward myosin may also be regulated. Examples in smooth muscle tissue are sparse, and the different mechanisms by which these processes may be adapted in uterine smooth muscle during pregnancy are not well-defined. Much research is needed to define further the cellular, biochemical, and molecular basis for these physiological processes involved in the regulation of uterine smooth muscle contraction and relaxation.
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Affiliation(s)
- R A Word
- Department of Obsterics and Gynecology, University of Texas Southwestern Medical Center at Dallas 75235-9032, USA
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55
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Ostrow BD, Chen P, Chisholm RL. Expression of a myosin regulatory light chain phosphorylation site mutant complements the cytokinesis and developmental defects of Dictyostelium RMLC null cells. J Biophys Biochem Cytol 1994; 127:1945-55. [PMID: 7806572 PMCID: PMC2120314 DOI: 10.1083/jcb.127.6.1945] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
In a number of systems phosphorylation of the regulatory light chain (RMLC) of myosin regulates the activity of myosin. In smooth muscle and vertebrate nonmuscle systems RMLC phosphorylation is required for contractile activity. In Dictyostelium discoideum phosphorylation of the RMLC regulates both ATPase activity and motor function. We have determined the site of phosphorylation on the Dictyostelium RMLC and used site-directed mutagenesis to replace the phosphorylated serine with an alanine. The mutant light chain was then expressed in RMLC null Dictyostelium cells (mLCR-) from an actin promoter on an integrating vector. The mutant RMLC was expressed at high levels and associated with the myosin heavy chain. RMLC bearing a ser13ala substitution was not phosphorylated in vitro by purified myosin light chain kinase, nor could phosphate be detected on the mutant RMLC in vivo. The mutant myosin had reduced actin-activated ATPase activity, comparable to fully dephosphorylated myosin. Unexpectedly, expression of the mutant RMLC rescued the primary phenotypic defects of the mlcR- cells to the same extent as did expression of wild-type RMLC. These results suggest that while phosphorylation of the Dictyostelium RMLC appears to be tightly regulated in vivo, it is not essential for myosin-dependent cellular functions.
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Affiliation(s)
- B D Ostrow
- Department of Cell, Molecular, and Structural Biology, Northwestern University Medical School, Chicago, Illinois 60611
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56
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Hammer JA. Regulation of Dictyostelium myosin II by phosphorylation: what is essential and what is important? J Cell Biol 1994; 127:1779-82. [PMID: 7806558 PMCID: PMC2120310 DOI: 10.1083/jcb.127.6.1779] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Affiliation(s)
- J A Hammer
- Laboratory of Cell Biology, National Institutes of Health, Bethesda, Maryland 20892-0301
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57
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Abstract
All conventional myosin IIs, whether isolated from skeletal, smooth, or invertebrate muscle sources, have two heads attached to an extended 16 nm alpha-helical coiled-coil tail. The head can be divided into a globular motor domain of approximately 770 amino acids that contains the catalytic and actin binding sites, and a neck region of approximately 70 amino acids which binds one essential and one regulatory light chain (ELC and RLC). The neck region with its associated LCs plays both structural and regulatory roles. While the mechanism and extent of regulation by the LCs varies for different myosins, the structural role may be a more fundamental feature of myosin II motors. Our understanding of the neck region has advanced rapidly in recent years primarily because of two types of information: (1) the high resolution structures of the LC binding domain from the thick-filament regulated scallop myosin (Xie et al., 1994) and of the head of unregulated skeletal myosin (Rayment et al., 1993), and (2) the ability to remove and/or mutate portions of both the heavy and light chains for analysis by in vitro motility assays.
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Affiliation(s)
- K M Trybus
- Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham MA 02254-9110
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58
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59
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Abstract
Unlike striated muscle cells, smooth muscle cells do not have an organized sarcomeric structure. However, all smooth muscle cells contain the contractile proteins, myosin, actin, and tropomyosin. Polymorphism of the myosin heavy chain exists in smooth muscle cells. Two myosin heavy chain (MHC) isoforms, SM1 (204 kDa) and SM2 (200 kDa), are present in smooth muscle cells; however, their ratios vary in smooth muscles from different sources. The hypertrophy of the urinary bladder induced by partial outlet obstruction in rabbits is associated with an alteration of the SM1-to-SM2 ratio from 1:3 to 1:1. Both heavy chains react with polyclonal antibody against smooth muscle myosin; however, antibody prepared against a peptide from the C-terminal region of the SM2 heavy chain cross-reacts only with the SM2 heavy chain. Removal of the obstruction reverses the bladder to normal mass with a concomitant change in the SM1-to-SM2 ratio back to 1:3. The expression of the SM1 mRNA is increased in response to obstruction-induced hypertrophy, and it also returns to normal upon removal of the obstruction. Urinary bladder smooth muscle contains predominantly gamma-actin. Obstruction-induced hypertrophy of the bladder smooth muscle is associated with an increase in the gamma-actin at both protein and mRNA levels. The beta-non-muscle actin is decreased and the alpha-smooth muscle actin is unchanged in response to obstruction-induced bladder hypertrophy. Contraction of all smooth muscles involves similar mechanisms. This review describes our current understanding of the mechanisms regulating contraction of the smooth muscle of the urinary bladder.
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Affiliation(s)
- S Chacko
- Department of Pathobiology, University of Pennsylvania, Philadelphia 19104
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60
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Fyrberg C, Parker H, Hutchison B, Fyrberg E. Drosophila melanogaster genes encoding three troponin-C isoforms and a calmodulin-related protein. Biochem Genet 1994; 32:119-35. [PMID: 7980384 DOI: 10.1007/bf00554420] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Using low-stringency hybridization and polymerase chain reaction (PCR)-based DNA amplification, we have isolated three Drosophila melanogaster genes that encode troponin-C isoforms and one specifying a protein that is closely related to calmodulin. Two of the troponin-C genes, located within the 47D and 73F subdivisions of chromosomes 2 and 3, respectively, encode very closely related isoforms. That specified by the 47D gene accumulates almost exclusively in larval muscles, while that encoded by the 73F gene is present in both larvae and adults. The third gene, located within the 41C subdivision of chromosome 2, encodes a more distantly related troponin-C isoform that accumulates only within adults. The gene that encodes the calmodulin-related protein is located within the 97A subdivision of chromosome three. The protein encoded by this gene has a different primary sequence from that of conventional calmodulin, which is specified by a gene located within the 49A subdivision of chromosome 2. Our report is the first to describe insect troponin-C isoforms and further avails genetic methods for investigating the in vivo functions of the troponin-C/myosin light-chain/calmodulin protein superfamily.
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Affiliation(s)
- C Fyrberg
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218
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61
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Cross-bridge cycling at rest and during activation. Turnover of myosin-bound ADP in permeabilized smooth muscle. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)37286-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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62
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Sweeney HL, Yang Z, Zhi G, Stull JT, Trybus KM. Charge replacement near the phosphorylatable serine of the myosin regulatory light chain mimics aspects of phosphorylation. Proc Natl Acad Sci U S A 1994; 91:1490-4. [PMID: 8108436 PMCID: PMC43185 DOI: 10.1073/pnas.91.4.1490] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Phosphorylation of the myosin regulatory light chains (RLCs) activates contraction in smooth muscle and modulates force production in striated muscle. RLC phosphorylation changes the net charge in a critical region of the N terminus and thereby may alter interactions between the RLC and myosin heavy chain. A series of N-terminal charge mutations in the human smooth muscle RLC has been engineered, and the mutants have been evaluated for their ability to mimic the phosphorylated form of the RLC when reconstituted into scallop striated muscle bundles or into isolated smooth muscle myosin. Changing the net charge in the region from Arg-13 to Ser-19 potentiates force in scallop striated muscle and maintains smooth muscle myosin in an unfolded filamentous state without affecting ATPase activity or motility of smooth muscle myosin. Thus, the effect of RLC phosphorylation in striated muscle and its ability to regulate the folded-to-extended conformational transition in smooth muscle may be due to a simple reduction of net charge at the N terminus of the light chain. The ability of phosphorylation to regulate smooth muscle myosin's ATPase activity and motility involves a more complex mechanism.
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Affiliation(s)
- H L Sweeney
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia 19104-6085
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63
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Moussavi RS, Kelley CA, Adelstein RS. Phosphorylation of vertebrate nonmuscle and smooth muscle myosin heavy chains and light chains. Mol Cell Biochem 1993; 127-128:219-27. [PMID: 7935353 DOI: 10.1007/bf01076773] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
In this article we review the various amino acids present in vertebrate nonmuscle and smooth muscle myosin that can undergo phosphorylation. The sites for phosphorylation in the 20 kD myosin light chain include serine-19 and threonine-18 which are substrates for myosin light chain kinase and serine-1 and/or -2 and threonine-9 which are substrates for protein kinase C. The sites in vertebrate smooth muscle and nonmuscle myosin heavy chains that can be phosphorylated by protein kinase C and casein kinase II are also summarized. Original data indicating that treatment of human T-lymphocytes (Jurkat cell line) with phorbol 12-myristate 13-acetate results in phosphorylation of both the 20 kD myosin light chain as well as the 200 kD myosin heavy chain is presented. We identified the amino acids phosphorylated in the human T-lymphocytes myosin light chains as serine-1 or serine-2 and in the myosin heavy chains as serine-1917 by 1-dimensional isoelectric focusing of tryptic phosphopeptides. Untreated T-lymphocytes contain phosphate in the serine-19 residue of the myosin light chain, and in a residue tentatively identified as serine-1944 in the myosin heavy chain.
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Affiliation(s)
- R S Moussavi
- Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
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64
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Venema RC, Raynor RL, Noland TA, Kuo JF. Role of protein kinase C in the phosphorylation of cardiac myosin light chain 2. Biochem J 1993; 294 ( Pt 2):401-6. [PMID: 8396912 PMCID: PMC1134468 DOI: 10.1042/bj2940401] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The role of protein kinase C (PKC) in the phosphorylation of myosin light chain 2 (MLC2) in adult rat heart cells has been investigated. PKC-mediated phosphorylation of MLC2 in adult rat cardiac myofibrils in vitro occurs with a stoichiometry (0.7 mol of phosphate/mol of protein) similar to that mediated by myosin light chain kinase (MLCK). Two-dimensional tryptic phosphopeptide mapping of MLC2 following phosphorylation by PKC or MLCK in vitro yields the same major phosphopeptides for each protein kinase. These sites are also 32P-labelled in situ when isolated cardiomyocytes are incubated with [32P]P(i). 32P labelling of MLC2 in cardiomyocytes is increased by 5-fold in 10 min upon incubation with the phosphatase inhibitor calyculin A, demonstrating the existence of a rapidly turning over component of MLC2 phosphorylation in these cells. 32P label is completely removed from MLC2 when myocytes are exposed to 2,3-butanedione monoxime, an inhibitor of cardiac contraction known to desensitize the myofilaments to activation by Ca2+. 32P labelling of MLC2 is also decreased by 50-100% following exposure to the PKC-selective inhibitors calphostin C and chelerythrine, suggesting that PKC, and not MLCK, is primarily responsible for incorporation of rapidly turning over phosphate into MLC2 in situ. Taken together, these data implicate PKC in the phosphorylation of MLC2 in heart cells and support the hypothesis that phosphorylation of cardiac MLC2 has a role in determining myofibrillar Ca2+ sensitivity.
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Affiliation(s)
- R C Venema
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322
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65
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Szymanski PT, Ferguson DG, Paul RJ. Polylysine activates smooth muscle myosin ATPase activity via induction of a 10S to 6S transition. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 265:C379-86. [PMID: 8368268 DOI: 10.1152/ajpcell.1993.265.2.c379] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Polylysine (10-13 kDa) stimulates contraction in smooth muscle skinned fibers and activates actomyosin adenosinetriphosphatase (ATPase) activity in the absence of myosin light chain phosphorylation [P. T. Szymanski and R. J. Paul. Adv. Exp. Med. 304: 363-368, 1991; P. T. Szymanski, J. D. Strauss, G. Doerman, J. DiSalvo, and R. J. Paul. Am J. Physiol. 262 (Cell Physiol. 31): C1445-C1455, 1992]. To provide further information on the mechanism of polylysine action on contractility in smooth muscle, we investigated its effect on ATPase activity and conformation of purified gizzard myosin. We report here that polylysine directly stimulates myosin ATPase activity in a concentration-dependent manner. This stimulation could be completely abolished with the addition of heparin, a negatively charged heteropolysaccharide. Polylysine (10 microM) increases myosin ATPase activity to a level similar to that of myosin phosphorylation. Addition of 10 microM polylysine to phosphorylated myosin [with myosin light chain kinase and adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), to approximately 1.9 mol P/mol myosin], however, did not further stimulate ATPase activity. At 0.2 M KCl (the salt concentration at which myosin exists primary in the 10S form), the addition of polylysine increases myosin ATPase activity to a level comparable to that of untreated myosin in 0.3 M KCl. These changes parallel the increase in solution viscosity elicited by polylysine. These results suggest that polylysine induces a transition in myosin conformation from the 10S to the 6S form, and this was confirmed by electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- P T Szymanski
- Department of Physiology and Biophysics, College of Medicine, University of Cincinnati, Ohio 45267-0576
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66
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Trybus K, Chatman T. Chimeric regulatory light chains as probes of smooth muscle myosin function. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53625-5] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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67
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Katoh T, Morita F. Actin-binding peptides obtained from the C-terminal 24-kDa fragment of porcine aorta smooth muscle myosin subfragment-1 heavy chain. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53787-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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68
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Drew JS, White MP, Stein LA. Smooth muscle myosin subfragment-1 is a kinetic analogue for heavy meromyosin in the extended conformation. CELL MOTILITY AND THE CYTOSKELETON 1993; 26:291-300. [PMID: 8299145 DOI: 10.1002/cm.970260404] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The 10S-->6S (Flexed-->Extended) transition in smooth muscle myosin is related to increased ATPase activity, but there is controversy over whether the analogous 9S-->7S transition in HMM is also associated with ATPase activity. We therefore studied the association of ionic strength, phosphorylation, and ATPase activity for HMM as compared to S1 which has no apparent flexed conformation. In addition, we performed both steady state and single turnover analyses, to control for artifacts due to multiple subfragment populations that might skew steady state results. At low ionic strength where myosin and HMM are in the flexed conformation, HMM had a near zero ATPase activity while S-1 had a high ATPase rate (0.07 s-1). At 400 mM ionic strength, where both myosin and HMM are in the extended conformation, S1 and HMM had the same ATPase rate (0.04 s-1). Phosphorylation did not affect S1 significantly, but shifted the HMM curve to higher rates at lower ionic strengths. Both steady state and single turnover experiments gave the same results, indicating that steady state results were not skewed by multiple subfragment populations. These data indicate that HMM has a conformation-ATPase relation similar to that observed with myosin. Furthermore, these findings suggest that the S1 ATPase rate corresponds to that of HMM in the extended conformation.
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Affiliation(s)
- J S Drew
- Department of Medicine, SUNY at Stony Brook 11794-8661
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69
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Sellers JR, Umemoto S, Cuda G. In vitro studies of determinants of smooth muscle mechanics. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1993; 332:267-76; discussion 276-7. [PMID: 8109341 DOI: 10.1007/978-1-4615-2872-2_26] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Smooth muscle contraction is dependent upon phosphorylation of the 20,000 Da light chain subunits of myosin. Whereas the kinetics of the hydrolysis of MgATP by smooth muscle myosin suggest a simple phosphorylation-dependent "on-off" mechanism, the contractile response in smooth muscle tissue is complex. Experiments to unravel this complexity have been performed in vitro using a combination of motility assays and kinetic techniques. Some insight into this complexity is obtained, but the mechanism and the regulation of smooth muscle contraction is still not completely known.
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Affiliation(s)
- J R Sellers
- Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, Bethesda, MD 20892
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70
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Inhibition of smooth muscle myosin's activity and assembly by an anti-rod monoclonal antibody. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)35721-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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71
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72
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Satterwhite LL, Lohka MJ, Wilson KL, Scherson TY, Cisek LJ, Corden JL, Pollard TD. Phosphorylation of myosin-II regulatory light chain by cyclin-p34cdc2: a mechanism for the timing of cytokinesis. J Cell Biol 1992; 118:595-605. [PMID: 1386367 PMCID: PMC2289554 DOI: 10.1083/jcb.118.3.595] [Citation(s) in RCA: 164] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
To understand how cytokinesis is regulated during mitosis, we tested cyclin-p34cdc2 for myosin-II kinase activity, and investigated the mitotic-specific phosphorylation of myosin-II in lysates of Xenopus eggs. Purified cyclin-p34cdc2 phosphorylated the regulatory light chain of cytoplasmic and smooth muscle myosin-II in vitro on serine-1 or serine-2 and threonine-9, sites known to inhibit the actin-activated myosin ATPase activity of smooth muscle and nonmuscle myosin (Nishikawa, M., J. R. Sellers, R. S. Adelstein, and H. Hidaka. 1984. J. Biol. Chem. 259:8808-8814; Bengur, A. R., A. E. Robinson, E. Appella, and J. R. Sellers. 1987. J. Biol. Chem. 262:7613-7617; Ikebe, M., and S. Reardon. 1990. Biochemistry. 29:2713-2720). Serine-1 or -2 of the regulatory light chain of Xenopus cytoplasmic myosin-II was also phosphorylated in Xenopus egg lysates stabilized in metaphase, but not in interphase. Inhibition of myosin-II by cyclin-p34cdc2 during prophase and metaphase could delay cytokinesis until chromosome segregation is initiated and thus determine the timing of cytokinesis relative to earlier events in mitosis.
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Affiliation(s)
- L L Satterwhite
- Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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73
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Vyas TB, Mooers SU, Narayan SR, Witherell JC, Siegman MJ, Butler TM. Cooperative activation of myosin by light chain phosphorylation in permeabilized smooth muscle. THE AMERICAN JOURNAL OF PHYSIOLOGY 1992; 263:C210-9. [PMID: 1386187 DOI: 10.1152/ajpcell.1992.263.1.c210] [Citation(s) in RCA: 107] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The purpose of this study was to determine the quantitative relationship between the number of myosin molecules that increase their ATPase activity and the degree of myosin light chain phosphorylation in smooth muscle. Single turnover experiments on the nucleotide bound to myosin were performed in the permeabilized rabbit portal vein. In the resting muscle, the rate of exchange of bound nucleoside diphosphate was biphasic and complete in approximately 30 min. When approximately 80% of the myosin light chain was thiophosphorylated, the nucleoside diphosphate exchange occurred at a much faster rate and was almost complete in 2 min. Thiophosphorylation of 10% of the myosin light chains caused an increase in the rate of ADP exchange from much more than 10% of the myosin subfragment-1. Less than 20% thiophosphorylation of the total myosin light chains resulted in the maximum increase in ADP exchanged in 2 min. It appears that a small degree of myosin light chain phosphorylation cooperatively turns on the maximum number of myosin molecules. Interestingly, even though less than 20% thiophosphorylation of the myosin light chain caused the maximum exchange of ADP within 2 min, higher degrees of thiophosphorylation were associated with further increases in the ATPase rates. We conclude that a small degree of myosin light chain thiophosphorylation cooperatively activates the maximum number of myosin molecules, and a higher degree of thiophosphorylation makes the myosin cycle faster. A kinetic model is proposed in which the rate constant for attachment of unphosphorylated cross bridges varies as a function of myosin light chain phosphorylation.
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Affiliation(s)
- T B Vyas
- Department of Physiology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
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74
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Warshaw D, Desrosiers J, Work S, Trybus K. Effects of MgATP, MgADP, and Pi on actin movement by smooth muscle myosin. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54234-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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75
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Stull JT, Gallagher PJ, Herring BP, Kamm KE. Vascular smooth muscle contractile elements. Cellular regulation. Hypertension 1991; 17:723-32. [PMID: 2045132 PMCID: PMC2836766 DOI: 10.1161/01.hyp.17.6.723] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
For many years the simple view was held that contractile force in smooth muscle was proportional to cytosolic Ca2+ concentrations ([Ca2+]i). With the discovery that phosphorylation of myosin light chain by Ca2+/calmodulin-dependent myosin light chain kinase initiated contraction, regulation of the contractile elements developed more complex properties. Molecular and biochemical investigations have identified important domains of myosin light chain kinase: light chain binding sites, catalytic core, pseudosubstrate prototope, and calmodulin-binding domain. New protein phosphatase inhibitors such as okadaic acid and calyculin A should help in the identification of the physiologically important phosphatase and potential modes of regulation. The proposal of an attached, dephosphorylated myosin cross bridge (latch bridge) that can maintain force has evoked considerable controversy about the detailed functions of the myosin phosphorylation system. The latch bridge has been defined by a model based on physiological properties but has not been identified biochemically. Thin-filament proteins have been proposed as secondary sites of regulation of contractile elements, but additional studies are needed to establish physiological roles. Changes in the Ca2+ sensitivity of smooth muscle contractile elements with different modes of cellular stimulation may be related to inactivation of myosin light chain kinase or activation of protein phosphatase activities. Thus, contractile elements in smooth muscle cells are not dependent solely on [Ca2+]i but use additional regulatory mechanisms. The immediate challenge is to define their relative importance and to describe molecular-biochemical properties that provide insights into proposed physiological functions.
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Affiliation(s)
- J T Stull
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235-9040
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76
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Ikebe M, Hewett TE, Martin AF, Chen M, Hartshorne DJ. Cleavage of a smooth muscle myosin heavy chain near its C terminus by alpha-chymotrypsin. Effect on the properties of myosin. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(20)89605-7] [Citation(s) in RCA: 14] [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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77
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Affiliation(s)
- J R Sellers
- Laboratory of Molecular Cardiology, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892
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78
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Abstract
It is well established that light chain phosphorylation is required before a smooth muscle can generate force. The apparent modulation of shortening velocity by phosphorylation during sustained contractions may be accounted for by a mechanical interaction between rapidly cycling phosphorylated crossbridges and slowly or non-cycling dephosphorylated crossbridges. Latchbridges, force-producing dephosphorylated crossbridges, have been proposed to explain why force levels remain high at low levels of phosphorylation. The role of the thin-filament-associated proteins caldesmon and calponin in regulation remains enigmatic, but their inhibitory properties in solution would be consistent with a possible involvement in maintenance of a relaxed state.
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Affiliation(s)
- K M Trybus
- Rosenstiel Research Center, Brandeis University, Waltham, MA 02254
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79
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Pollenz RS, Chisholm RL. Dictyostelium discoideum essential myosin light chain: gene structure and characterization. CELL MOTILITY AND THE CYTOSKELETON 1991; 20:83-94. [PMID: 1751970 DOI: 10.1002/cm.970200202] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have used a Dictyostelium essential myosin light chain (EMLC) cDNA clone to isolate additional cDNA clones which supply a different 3' sequence from that previously described. The revised cDNA sequence encodes a polypeptide of 150 amino acids. Amino acid residues 147-167 of the previously reported sequence are replaced by new residues 147 to 150. The new cDNA encodes a polypeptide with 66% amino acid sequence identity with the Physarum polycephalum EMLC, and approximately 30% identity with mammalian EMLC sequences. These new cDNA clones were used to isolate two genomic DNA fragments which contain the entire EMLC gene. The Dictyostelium EMLC gene contains a single intron located immediately 3' of the translation initiation codon and encodes a product most similar to MLC3 isoform of vertebrates. Primer extension analysis places the transcription initiation site approximately 90 nucleotides upstream of the translation initiation site. A DNA fragment containing 350 bases of sequence upstream of the putative transcription initiation site is sufficient to drive expression of a reporter gene upon reintroduction into growing Dictyostelium cells. In addition, the CAT reporter mRNA produced by this construct showed a pattern of developmental regulation similar to that previously reported for the endogenous EMLC mRNA. Based on comparison with published EMLC sequences from a variety of sources, the Dictyostelium EMLC shows slightly higher similarity to vertebrate EMLCs from striated muscle sources than nonmuscle sources. While Dictyostelium and human nonmuscle sequences display only 28% identity over their entire sequence, the region from residue 88 to 108 shows much higher identity (67%). The high evolutionary conservation of this region of the EMLC suggests it may play an important role in EMLC function, and as such, represents a good target for future mutagenesis studies.
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Affiliation(s)
- R S Pollenz
- Department of Cell, Molecular and Structural Biology, Northwestern University Medical School, Chicago, IL 60611
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80
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Szymanski PT, Paul RJ. Polylysine: an activator of smooth muscle contractility. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1991; 304:363-8. [PMID: 1839486 DOI: 10.1007/978-1-4684-6003-2_28] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- P T Szymanski
- Department of Physiology and Biophysics, University of Cincinnati, College of Medicine, OH 45267
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81
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Rimm DL, Kaiser DA, Bhandari D, Maupin P, Kiehart DP, Pollard TD. Identification of functional regions on the tail of Acanthamoeba myosin-II using recombinant fusion proteins. I. High resolution epitope mapping and characterization of monoclonal antibody binding sites. J Biophys Biochem Cytol 1990; 111:2405-16. [PMID: 1703536 PMCID: PMC2116414 DOI: 10.1083/jcb.111.6.2405] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
We used a series of COOH-terminally deleted recombinant myosin molecules to map precisely the binding sites of 22 monoclonal antibodies along the tail of Acanthamoeba myosin-II. These antibodies bind to 14 distinguishable epitopes, some separated by less than 10 amino acids. The positions of the binding sites visualized by electron microscopy agree only approximately with the physical positions of these sites on the alpha-helical coiled-coil tail. On the other hand, the epitope map agrees precisely with competitive binding studies: all antibodies that share an epitope compete with each other for binding to myosin. Antibodies with adjacent epitopes can compete with each other at linear distances up to 5 or 6 nm, and many antibodies that bind 3-7-nm apart can enhance the binding of each other to myosin. Most of the antibodies that bind to the distal 37 nm of the tail disrupt assembly of octameric minifilaments and, depending upon the exact location of the binding site, stop assembly at specific steps yielding, for example, monomers, antiparallel dimers, parallel dimers or antiparallel tetramers. The effects of these antibodies on assembly identify sites on the tail that are required for individual steps in minifilament assembly. Experiments on the assembly of truncated myosin-II tails have revealed a complementary group of sites that participate in the assembly reactions (Sinard, J.H., D.L. Rimm, and T.D. Pollard. 1990. J. Cell Biol. 111:2417-2426). Antibodies that bind to the distal tail but do not affect assembly appear to have a low affinity for myosin-II. Antibodies that bind to the proximal 50 nm of the tail do not inhibit the assembly of minifilaments. Many antibodies that bind to the tail of myosin-II, even some that have no obvious effect on minifilament assembly, can inhibit the actomyosin ATPase activity and the contraction of an actin gel formed in crude extracts. An antibody that binds between amino acids 1447 and 1467 inhibits the phosphorylation of serine residues distal to residue 1483.
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Affiliation(s)
- D L Rimm
- Department of Cell Biology and Anatomy, Johns Hopkins Medical School, Baltimore, Maryland 21205
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82
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Warshaw DM, Desrosiers JM, Work SS, Trybus KM. Smooth muscle myosin cross-bridge interactions modulate actin filament sliding velocity in vitro. J Biophys Biochem Cytol 1990; 111:453-63. [PMID: 2143195 PMCID: PMC2116193 DOI: 10.1083/jcb.111.2.453] [Citation(s) in RCA: 213] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Although it is generally believed that phosphorylation of the regulatory light chain of myosin is required before smooth muscle can develop force, it is not known if the overall degree of phosphorylation can also modulate the rate at which cross-bridges cycle. To address this question, an in vitro motility assay was used to observe the motion of single actin filaments interacting with smooth muscle myosin copolymers composed of varying ratios of phosphorylated and unphosphorylated myosin. The results suggest that unphosphorylated myosin acts as a load to slow down the rate at which actin is moved by the faster cycling phosphorylated cross-bridges. Myosin that was chemically modified to generate a noncycling analogue of the "weakly" bound conformation was similarly able to slow down phosphorylated myosin. The observed modulation of actin velocity as a function of copolymer composition can be accounted for by a model based on mechanical interactions between cross-bridges.
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Affiliation(s)
- D M Warshaw
- Department of Physiology and Biophysics, University of Vermont, College of Medicine, Burlington 05405
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83
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Trybus KM, Henry L. Monoclonal antibodies detect and stabilize conformational states of smooth muscle myosin. J Biophys Biochem Cytol 1989; 109:2879-86. [PMID: 2480352 PMCID: PMC2115922 DOI: 10.1083/jcb.109.6.2879] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Antibodies with epitopes near the heavy meromyosin/light meromyosin junction distinguish the folded from the extended conformational states of smooth muscle myosin. Antibody 10S.1 has 100-fold higher avidity for folded than for extended myosin, while antibody S2.2 binds preferentially to the extended state. The properties of these antibodies provide direct evidence that the conformation of the rod is different in the folded than the extended monomeric state, and suggest that this perturbation may extend into the subfragment 2 region of the rod. Two antihead antibodies with epitopes on the heavy chain map at or near the head/rod junction. Magnesium greatly enhances the binding of these antibodies to myosin, showing that the conformation of the heavy chain in the neck region changes upon divalent cation binding to the regulatory light chain. Myosin assembly is also altered by antibody binding. Antibodies that bind to the central region of the rod block disassembly of filaments upon MgATP addition. Antibodies with epitopes near the COOH terminus of the rod, in contrast, promote filament depolymerization, suggesting that this region of the tail is important for assembly. The monoclonal antibodies described here are therefore useful both for detecting and altering conformational states of smooth muscle myosin.
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Affiliation(s)
- K M Trybus
- Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02254-9110
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