Journal: J Struct Biol / Year: 2017 Title: Relaxed and active thin filament structures; a new structural basis for the regulatory mechanism. Authors: Danielle M Paul / John M Squire / Edward P Morris / Abstract: The structures of muscle thin filaments reconstituted using skeletal actin and cardiac troponin and tropomyosin have been determined with and without bound Ca using electron microscopy and reference- ...The structures of muscle thin filaments reconstituted using skeletal actin and cardiac troponin and tropomyosin have been determined with and without bound Ca using electron microscopy and reference-free single particle analysis. The resulting density maps have been fitted with atomic models of actin, tropomyosin and troponin showing that: (i) the polarity of the troponin complex is consistent with our 2009 findings, with large shape changes in troponin between the two states; (ii) without Ca the tropomyosin pseudo-repeats all lie at almost equivalent positions in the 'blocked' position on actin (over subdomains 1 and 2); (iii) in the active state the tropomyosin pseudo-repeats are all displaced towards subdomains 3 and 4 of actin, but the extent of displacement varies within the regulatory unit depending upon the axial location of the pseudo-repeats with respect to troponin. Individual pseudo-repeats with Ca bound to troponin can be assigned either to the 'closed' state, a partly activated conformation, or the 'M-state', a fully activated conformation which has previously been thought to occur only when myosin heads bind. These results lead to a modified view of the steric blocking model of thin filament regulation in which cooperative activation is governed by troponin-mediated local interactions of the pseudo-repeats of tropomyosin with actin.
History
Deposition
Jan 17, 2017
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Header (metadata) release
Jul 5, 2017
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Map release
Feb 14, 2018
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Update
Oct 24, 2018
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Current status
Oct 24, 2018
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
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