Troponin Revealed: Uncovering the Structure of the Thin Filament On-Off Switch in Striated Muscle.

Biophysical Journal
L S Tobacman

Abstract

Recently, our understanding of the structural basis of troponin-tropomyosin's Ca2+-triggered regulation of striated muscle contraction has advanced greatly, particularly via cryo-electron microscopy data. Compelling atomic models of troponin-tropomyosin-actin were published for both apo- and Ca2+-saturated states of the cardiac thin filament. Subsequent electron microscopy and computational analyses have supported and further elaborated the findings. Per cryo-electron microscopy, each troponin is highly extended and contacts both tropomyosin strands, which lie on opposite sides of the actin filament. In the apo-state characteristic of relaxed muscle, troponin and tropomyosin hinder strong myosin-actin binding in several different ways, apparently barricading the actin more substantially than does tropomyosin alone. The troponin core domain, the C-terminal third of TnI, and tropomyosin under the influence of a 64-residue helix of TnT located at the overlap of adjacent tropomyosins are all in positions that would hinder strong myosin binding to actin. In the Ca2+-saturated state, the TnI C-terminus dissociates from actin and binds in part to TnC; the core domain pivots significantly; the N-lobe of TnC binds specifically to actin ...Continue Reading

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Citations

Jan 26, 2021·The Journal of General Physiology·Larry S Tobacman, Anthony Cammarato
Mar 15, 2021·Biochemical and Biophysical Research Communications·William LehmanMichael J Rynkiewicz
Mar 20, 2021·The Journal of General Physiology·Christopher Solís, R John Solaro

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