Single-molecule imaging reveals the concerted release of myosin from regulated thin filaments

eLife

Hongsheng Dai¹  Madalina-Daniela Mihailescu¹  Quentin M Smith²  Alessio V Inchingolo²  Neil M Kad² 

[1] Department of Mathematical Sciences, University of Essex, Colchester, United Kingdom;School of Biosciences, University of Kent, Canterbury, United Kingdom;

关键词: cooperativity;    muscle;    actin;    fluorescence imaging;    regulation;    calcium;    Chicken;    E. coli;    Human;   

DOI  :  10.7554/eLife.69184

来源: eLife Sciences Publications, Ltd

【 摘 要 】

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.

【 授权许可】

CC BY