Troponin Structural Dynamics in the Native Cardiac Thin Filament Revealed by Cryo Electron Microscopy
Copyright © 2024 Elsevier Ltd. All rights reserved..
Cardiac muscle contraction occurs due to repetitive interactions between myosin thick and actin thin filaments (TF) regulated by Ca2+ levels, active cross-bridges, and cardiac myosin-binding protein C (cMyBP-C). The cardiac TF (cTF) has two nonequivalent strands, each comprised of actin, tropomyosin (Tm), and troponin (Tn). Tn shifts Tm away from myosin-binding sites on actin at elevated Ca2+ levels to allow formation of force-producing actomyosin cross-bridges. The Tn complex is comprised of three distinct polypeptides - Ca2+-binding TnC, inhibitory TnI, and Tm-binding TnT. The molecular mechanism of their collective action is unresolved due to lack of comprehensive structural information on Tn region of cTF. C1 domain of cMyBP-C activates cTF in the absence of Ca2+ to the same extent as rigor myosin. Here we used cryo-EM of native cTFs to show that cTF Tn core adopts multiple structural conformations at high and low Ca2+ levels and that the two strands are structurally distinct. At high Ca2+ levels, cTF is not entirely activated by Ca2+ but exists in either partially or fully activated state. Complete dissociation of TnI C-terminus is required for full activation. In presence of cMyBP-C C1 domain, Tn core adopts a fully activated conformation, even in absence of Ca2+. Our data provide a structural description for the requirement of myosin to fully activate cTFs and explain increased affinity of TnC to Ca2+ in presence of active cross-bridges. We suggest that allosteric coupling between Tn subunits and Tm is required to control actomyosin interactions.
| Medienart: |
E-Artikel |
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| Erscheinungsjahr: |
2024 |
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| Erschienen: |
2024 |
| Enthalten in: |
Zur Gesamtaufnahme - volume:436 |
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| Enthalten in: |
Journal of molecular biology - 436(2024), 6 vom: 15. März, Seite 168498 |
| Sprache: |
Englisch |
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| Beteiligte Personen: |
Risi, Cristina M [VerfasserIn] |
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| Links: |
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| Themen: |
9013-26-7 |
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| Anmerkungen: |
Date Completed 18.03.2024 Date Revised 25.04.2024 published: Print-Electronic Citation Status MEDLINE |
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| doi: |
10.1016/j.jmb.2024.168498 |
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| funding: |
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| Förderinstitution / Projekttitel: |
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| 520 | |a Cardiac muscle contraction occurs due to repetitive interactions between myosin thick and actin thin filaments (TF) regulated by Ca2+ levels, active cross-bridges, and cardiac myosin-binding protein C (cMyBP-C). The cardiac TF (cTF) has two nonequivalent strands, each comprised of actin, tropomyosin (Tm), and troponin (Tn). Tn shifts Tm away from myosin-binding sites on actin at elevated Ca2+ levels to allow formation of force-producing actomyosin cross-bridges. The Tn complex is comprised of three distinct polypeptides - Ca2+-binding TnC, inhibitory TnI, and Tm-binding TnT. The molecular mechanism of their collective action is unresolved due to lack of comprehensive structural information on Tn region of cTF. C1 domain of cMyBP-C activates cTF in the absence of Ca2+ to the same extent as rigor myosin. Here we used cryo-EM of native cTFs to show that cTF Tn core adopts multiple structural conformations at high and low Ca2+ levels and that the two strands are structurally distinct. At high Ca2+ levels, cTF is not entirely activated by Ca2+ but exists in either partially or fully activated state. Complete dissociation of TnI C-terminus is required for full activation. In presence of cMyBP-C C1 domain, Tn core adopts a fully activated conformation, even in absence of Ca2+. Our data provide a structural description for the requirement of myosin to fully activate cTFs and explain increased affinity of TnC to Ca2+ in presence of active cross-bridges. We suggest that allosteric coupling between Tn subunits and Tm is required to control actomyosin interactions | ||
| 650 | 4 | |a Journal Article | |
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| 650 | 4 | |a muscle regulation | |
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| 650 | 4 | |a thin filament | |
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| 700 | 1 | |a Belknap, Betty |e verfasserin |4 aut | |
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| 700 | 1 | |a Pinto, Jose R |e verfasserin |4 aut | |
| 700 | 1 | |a Galkin, Vitold E |e verfasserin |4 aut | |
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