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Relaxed and active thin filament structures; a new structural basis for the regulatory mechanism
The structures of muscle thin filaments reconstituted using skeletal actin and cardiac troponin and tropomyosin have been determined with and without bound Ca(2+) using electron microscopy and reference-free single particle analysis. The resulting density maps have been fitted with atomic models of...
Autores principales: | , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
Academic Press
2017
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5367448/ https://www.ncbi.nlm.nih.gov/pubmed/28161413 http://dx.doi.org/10.1016/j.jsb.2017.01.004 |
Sumario: | The structures of muscle thin filaments reconstituted using skeletal actin and cardiac troponin and tropomyosin have been determined with and without bound Ca(2+) 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(2+) 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(2+) 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. |
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