Smith, Quentin M and Inchingolo, Alessio V and Mihailescu, Madalina-Daniela and Dai, Hongsheng and Kad, Neil M (2021) 'Single molecule imaging reveals the concerted release of myosin from regulated thin filaments.' eLife, 2021 (10). e69184-. ISSN 2050-084X

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Abstract

Regulated thin filaments (RTFs) tightly control striated muscle contraction through calcium binding to troponin, which enables tropomyosin to expose myosin-binding sites on actin. Myosin binding holds tropomyosin in an open position, exposing more myosin-binding sites on actin, leading to cooperative activation. At lower calcium levels, troponin and tropomyosin turn off the thin filament; however, this is antagonised by the high local concentration of myosin, questioning how the thin filament relaxes. To provide molecular details of deactivation, we used single-molecule imaging of green fluorescent protein (GFP)-tagged myosin-S1 (S1-GFP) to follow the activation of RTF tightropes. In sub-maximal activation conditions, RTFs are not fully active, enabling direct observation of deactivation in real time. We observed that myosin binding occurs in a stochastic step-wise fashion; however, an unexpectedly large probability of multiple contemporaneous detachments is observed. This suggests that deactivation of the thin filament is a coordinated active process.

Item Type:	Article
Uncontrolled Keywords:	Humans; Myosins; Troponin; Green Fluorescent Proteins; Stochastic Processes; Protein Binding; Muscle, Striated; Actin Cytoskeleton; Single Molecule Imaging
Divisions:	Faculty of Science and Health Faculty of Science and Health > Mathematical Sciences, Department of
SWORD Depositor:	Elements
Depositing User:	Elements
Date Deposited:	28 Sep 2021 15:32
Last Modified:	16 May 2022 16:44
URI:	http://repository.essex.ac.uk/id/eprint/31186

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