AI Article Synopsis

  • Regulated thin filaments (RTFs) control muscle contraction by allowing calcium to bind to troponin, which exposes myosin-binding sites on actin.
  • Myosin binding helps maintain the open position of tropomyosin, promoting cooperative activation of the muscle.
  • Using single-molecule imaging with GFP-tagged myosin, researchers found that the deactivation of RTFs is a coordinated active process, involving stochastic binding and a high likelihood of simultaneous detachments.

Article 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.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8476120PMC
http://dx.doi.org/10.7554/eLife.69184DOI Listing

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