Cross-helix separation of tropomyosin molecules in acto-tropomyosin as determined by neutron scattering

Bivin, Donald B.; Stone, Deborah B.; Schneider, Dieter K.; Mendelson, Robert A.

doi:10.1016/s0006-3495(91)82300-1

Cited by 13 publications

(6 citation statements)

References 28 publications

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“…There is reasonable agreement in the literature that the radius of the binding of Tm to actin does not significantly change in response to Ca 2+ binding. 27 For the model herein, the radii changed slightly (by 1-2 Å).…”

Section: Discussionmentioning

confidence: 91%

A Three-Dimensional FRET Analysis to Construct an Atomic Model of the Actin–Tropomyosin Complex on a Reconstituted Thin Filament

Miki

Makimura

Saitoh

et al. 2011

Journal of Molecular Biology

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Fluorescence resonance energy transfer (FRET) was used to construct an atomic model of the actin-tropomyosin (Tm) complex on a reconstituted thin filament. We generated five single-cysteine mutants in the 146-174 region of rabbit skeletal muscle α-Tm. An energy donor probe was attached to a single-cysteine Tm residue, while an energy acceptor probe was located in actin Gln41, actin Cys374, or the actin nucleotide binding site. From these donor-acceptor pairs, FRET efficiencies were determined with and without Ca(2+). Using the atomic coordinates for F-actin and Tm, we searched all possible arrangements for Tm segment 146-174 on F-actin to calculate the FRET efficiency for each donor-acceptor pair in each arrangement. By minimizing the squared sum of deviations for the calculated FRET efficiencies from the observed FRET efficiencies, we determined the location of the Tm segment on the F-actin filament. Furthermore, we generated a set of five single-cysteine mutants in each of the four Tm regions 41-69, 83-111, 216-244, and 252-279. Using the same procedures, we determined each segment's location on the F-actin filament. In the best-fit model, Tm runs along actin residues 217-236, which were reported to compose the Tm binding site. Electrostatic, hydrogen-bonding, and hydrophobic interactions are involved in actin and Tm binding. The C-terminal region of Tm was observed to contact actin more closely than did the N-terminal region. Tm contacts more residues on actin without Ca(2+) than with it. Ca(2+)-induced changes on the actin-Tm contact surface strongly affect the F-actin structure, which is important for muscle regulation.

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Section: Discussionmentioning

confidence: 91%

A Three-Dimensional FRET Analysis to Construct an Atomic Model of the Actin–Tropomyosin Complex on a Reconstituted Thin Filament

Miki

Makimura

Saitoh

et al. 2011

Journal of Molecular Biology

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“…While F-actin may be a platform for tropomyosin binding, it was also soon appreciated that the binding interaction of the two is so weak (226) that actin and tropomyosin helices could be considered semiautonomous "cofilaments" where the tropomyosin cable "floats" over actin on a sea of charged amino acids [see Holmes and Lehman (89) for further discussion]. Indeed, fiber diffraction studies and EM reconstruction subsequently showed that on average tropomyosin lies about 10Å above the surface of actin subunits at a radius of 39 to 42Å from the central axis of the thin filament, thus precluding strong stereospecific binding of tropomyosin and actin (9,140,183). In contrast, the separation is consistent with weak electrostatic interactions dominating the actin-tropomyosin association without preventing azimuthal movement of tropomyosin on actin in response to troponin, Ca 2+ and myosin binding to thin filaments (16,138,140,183).…”

Section: Steric Hindrance By Tropomyosinmentioning

confidence: 99%

Thin Filament Structure and the Steric Blocking Model

Lehman

2016

Comprehensive Physiology

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By interacting with the troponin-tropomyosin complex on myofibrillar thin filaments, Ca2+ and myosin govern the regulatory switching processes influencing contractile activity of mammalian cardiac and skeletal muscles. A possible explanation of the roles played by Ca2+ and myosin emerged in the early 1970s when a compelling "steric model" began to gain traction as a likely mechanism accounting for muscle regulation. In its most simple form, the model holds that, under the control of Ca2+ binding to troponin and myosin binding to actin, tropomyosin strands running along thin filaments either block myosin-binding sites on actin when muscles are relaxed or move away from them when muscles are activated. Evidence for the steric model was initially based on interpretation of subtle changes observed in X-ray fiber diffraction patterns of intact skeletal muscle preparations. Over the past 25 years, electron microscopy coupled with three-dimensional reconstruction directly resolved thin filament organization under many experimental conditions and at increasingly higher resolution. At low-Ca2+, tropomyosin was shown to occupy a "blocked-state" position on the filament, and switched-on in a two-step process, involving first a movement of tropomyosin away from the majority of the myosin-binding site as Ca2+ binds to troponin and then a further movement to fully expose the site when small numbers of myosin heads bind to actin. In this contribution, basic information on Ca2+-regulation of muscle contraction is provided. A description is then given relating the voyage of discovery taken to arrive at the present understanding of the steric regulatory model.

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“…Neutron scattering observed at this "contrast matching" point thus arises primarily from the deuterated component. This technique and the related contrast variation method have been successfully applied to investigate in situ structures of various muscle proteins 22,23 including the TnC-TnI complex 24 and the whole Tn complex. [25][26][27] Here, as a first step towards obtaining the in situ structural information of each subunit of Tn complex within the thin filaments, the structure of TnC within the thin filaments was investigated with neutron scattering.…”

Section: Introductionmentioning

confidence: 99%

Conformational Changes of Troponin C Within the Thin Filaments Detected by Neutron Scattering

Matsumoto¹,

Makino

Maéda

et al. 2004

Journal of Molecular Biology

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Cross-helix separation of tropomyosin molecules in acto-tropomyosin as determined by neutron scattering

Cited by 13 publications

References 28 publications

A Three-Dimensional FRET Analysis to Construct an Atomic Model of the Actin–Tropomyosin Complex on a Reconstituted Thin Filament

A Three-Dimensional FRET Analysis to Construct an Atomic Model of the Actin–Tropomyosin Complex on a Reconstituted Thin Filament

Thin Filament Structure and the Steric Blocking Model

Conformational Changes of Troponin C Within the Thin Filaments Detected by Neutron Scattering

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