Solution NMR Structure of the Junction between Tropomyosin Molecules: Implications for Actin Binding and Regulation

Greenfield, Norma J.; Huang, Yuanpeng Janet; Swapna, G.V.T.; Bhattacharya, Aneerban; Rapp, Brian; Singh, Abhishek; Montelione, Gaetano T.; Hitchcock‐DeGregori, Sarah E.

doi:10.1016/j.jmb.2006.08.033

Cited by 132 publications

(226 citation statements)

References 65 publications

(121 reference statements)

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“…Mutations in the first-half of periods 2-6 are in red, and mutations in the second-half are in blue. The periodic repeats do not correspond to the half-turns of the coiled-coil in the 7 Å structure because there are five and three-quarter half-turns of the supercoil per molecule, not seven (43,44). That is, the half-turns do not correspond to the seven actins along the length of one Tm molecule.…”

Section: Resultsmentioning

confidence: 99%

Regulation of actin-myosin interaction by conserved periodic sites of tropomyosin

Barua

Winkelmann

White

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Cooperative activation of actin-myosin interaction by tropomyosin (Tm) is central to regulation of contraction in muscle cells and cellular and intracellular movements in nonmuscle cells. The steric blocking model of muscle regulation proposed 40 y ago has been substantiated at both the kinetic and structural levels. Even with atomic resolution structures of the major players, how Tm binds and is designed for regulatory function has remained a mystery. Here we show that a set of periodically distributed evolutionarily conserved surface residues of Tm is required for cooperative regulation of actomyosin. Based on our results, we propose a model of Tm on a structure of actin-Tm-myosin in the "open" (on) state showing potential electrostatic interactions of the residues with both actin and myosin. The sites alternate with a second set of conserved surface residues that are important for actin binding in the inhibitory state in the absence of myosin. The transition from the closed to open states requires the sites identified here, even when troponin + Ca 2+ is present. The evolutionarily conserved residues are important for actomyosin regulation, a universal function of Tm that has a common structural basis and mechanism.actin filament structure | cell motility | cytoskeleton | muscle contraction | motility assay A ctin and myosin are found in almost all eukaryotic cells and are required for diverse cellular functions, including muscle contraction, cell motility, cell adhesion, cytokinesis, and organelle transport (1). The actin-myosin interaction produces two types of movements: force generation between actin filaments leading to contractions, such as in muscle contraction, cell motility, and cytokinesis; and transport of subcellular organelles and macromolecular complexes by myosin motors along actin filaments. The actomyosin contractile apparatus is best characterized in striated muscle contraction, which is regulated in a Ca 2+ -dependent manner by the proteins, tropomyosin (Tm) and troponin (Tn).Tm is a universal regulator of the actin cytoskeleton. It is a twochained, α-helical coiled-coil actin binding protein that associates end-to-end to form a continuous strand along both sides of actin filaments and regulates the functions and stability of actin filaments (2, 3). Tm regulates the interaction of actin filaments with actin binding proteins, including myosin, Tn, ADF-cofilin, Arp2/3, formin, and tropomodulin. Tm can activate or inhibit actomyosin, depending on the myosin and Tm isoforms (4-7). The Tm-dependent regulation is widespread, having been reported in fission yeast and mammalian muscle and nonmuscle systems. The regulation of actomyosin by Tm may be viewed as universal, although there is little understanding of the mechanism or structural basis, the focus of the present work.In striated muscle, regulation of myosin binding to the thin filament (actin-Tm-Tn) is described by a three-state model, where the three kinetic states are thought to correspond to three positions of Tm on the actin filament (8-1...

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Section: Resultsmentioning

confidence: 99%

Regulation of actin-myosin interaction by conserved periodic sites of tropomyosin

Barua

Winkelmann

White

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…To achieve this, they proposed that the tropomyosin coiled-coil pitch was 137 Å and that successive molecules overlapped by 7-11 residues in a way that did not result in an abrupt change in coiled-coil rotation. Subsequent work indicated that, at least in some instances, the rotation angle of the coiled coil changes by Ϸ90°between successive molecules (24,26). Such a change would mean that the interaction geometry between alternate tropomyosins and actin would be different.…”

Section: Implications For Regulation Of Striated Muscle Contractionmentioning

confidence: 99%

Structural basis for tropomyosin overlap in thin (actin) filaments and the generation of a molecular swivel by troponin-T

Murakami

Stewart

Nozawa

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

103

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-C caused a marked decrease in the affinity of troponin for actin-tropomyosin filaments. The highly conserved region of TnT, in which most cardiomyopathy mutations reside, is crucial for interacting with tropomyosin. The structure of the ternary complex also explains why the skeletal-and cardiac-muscle specific C-terminal region is required to bind TnT and why tropomyosin homodimers bind only a single TnT. On actin filaments, the head-to-tail junction can function as a molecular swivel to accommodate irregularities in the coiled-coil path between successive tropomyosins enabling each to interact equivalently with the actin helix.calcium ͉ cardiomyopathy ͉ troponin

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“…The C-terminal and N-terminal sequences of tropomyosin are crucial to the normal head-to-tail polymerisation of tropomyosin. 33 Therefore, it might be surmised that the tropomyosin resulting from the mutation described here, with added uncoiled protein at the C-terminal end of the molecule, would not be able to form the coiled-coil polymer that normally runs the length of the thin filament. On the other hand, tropomyosins fused to non-coiled-coil fluorescent proteins can incorporate into sarcomeres suggesting that the mutant tropomyosin in these families might not be completely non-functional.…”

Section: Discussionmentioning

confidence: 93%

Identification of a founder mutation in TPM3 in nemaline myopathy patients of Turkish origin

et al. 2008

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To date, six genes are known to cause nemaline (rod) myopathy (NM), a rare congenital neuromuscular disorder. In an attempt to find a seventh gene, we performed linkage and subsequent sequence analyses in 12 Turkish families with recessive NM. We found homozygosity in two of the families at 1q12-21.2, a region encompassing the c-tropomyosin gene (TPM3) encoding slow skeletal muscle a-tropomyosin, a known NM gene. Sequencing revealed homozygous deletion of the first nucleotide of the last exon, c.913delA of TPM3 in both families. The mutation removes the last nucleotide before the stop codon, causing a frameshift and readthrough across the termination signal. The encoded aTm slow protein is predicted to be 73 amino acids longer than normal, and the extension to the protein is hypothesised to be unable to form a coiled coil. The resulting tropomyosin protein may therefore be non-functional. The affected children in both families were homozygous for the mutation, while the healthy parents were mutation carriers. Both of the patients in Family 1 had the severe form of NM, and also an unusual chest deformity. The affected children in Family 2 had the intermediate form of NM. Muscle biopsies showed type 1 (slow) fibres to be markedly smaller than type 2 (fast) fibres. Previously, there had been five reports, only, of NM caused by mutations in TPM3. The mutation reported here is the first deletion to be identified in TPM3, and it is likely to be a founder mutation in the Turkish population.

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Solution NMR Structure of the Junction between Tropomyosin Molecules: Implications for Actin Binding and Regulation

Cited by 132 publications

References 65 publications

Regulation of actin-myosin interaction by conserved periodic sites of tropomyosin

Regulation of actin-myosin interaction by conserved periodic sites of tropomyosin

Structural basis for tropomyosin overlap in thin (actin) filaments and the generation of a molecular swivel by troponin-T

Identification of a founder mutation in TPM3 in nemaline myopathy patients of Turkish origin

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