8UWX

The structure of the native cardiac thin filament troponin core in Ca2+-free tilted state from the upper strand

Summary for 8UWX

• Entry DOI: 10.2210/pdb8uwx/pdb
• EMDB information: 42682
• Descriptor: Actin, alpha cardiac muscle 1, Troponin C, slow skeletal and cardiac muscles, Troponin I, cardiac muscle, ... (5 entities in total)
• Functional Keywords: thin filament, troponin, tropomyosin, cryo-em, muscle structure, motor protein
• Biological source: Sus scrofa (pig); More
• Total number of polymer chains: 7
• Total formula weight: 226123.02

Authors

Galkin, V.E.,Risi, C.M. (deposition date: 2023-11-08, release date: 2024-03-06, Last modification date: 2024-03-13)

Primary citation

Risi, C.M.,Belknap, B.,Atherton, J.,Coscarella, I.L.,White, H.D.,Bryant Chase, P.,Pinto, J.R.,Galkin, V.E.
Troponin Structural Dynamics in the Native Cardiac Thin Filament Revealed by Cryo Electron Microscopy.
J.Mol.Biol., 436:168498-168498, 2024

PubMed Abstract: Cardiac muscle contraction occurs due to repetitive interactions between myosin thick and actin thin filaments (TF) regulated by Ca 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 Ca levels to allow formation of force-producing actomyosin cross-bridges. The Tn complex is comprised of three distinct polypeptides - Ca-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 Ca 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 Ca levels and that the two strands are structurally distinct. At high Ca levels, cTF is not entirely activated by Ca 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 Ca. Our data provide a structural description for the requirement of myosin to fully activate cTFs and explain increased affinity of TnC to Ca in presence of active cross-bridges. We suggest that allosteric coupling between Tn subunits and Tm is required to control actomyosin interactions.

PubMed: 38387550
DOI: 10.1016/j.jmb.2024.168498

Experimental method

ELECTRON MICROSCOPY (6 Å)