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Excitation-contraction coupling is a series of events that occur between generating an action potential and initiating a muscle contraction. It occurs at the triad, a structure found in skeletal muscle fibers that comprise a T-tubule and terminal cisternae of the sarcoplasmic reticulum on each side. These triads are visible in longitudinally sectioned muscle fibers. They are typically located at the A-I junction — the junction between the A and I bands of the sarcomere.
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Smooth muscle contraction is a complex process vital for various bodily functions, from maintaining blood vessel tension to facilitating the movement of food through the digestive tract. Unlike striated muscles, smooth muscle contraction begins more slowly and lasts longer.
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Actin and myosin are contractile proteins that form the sarcomere found in skeletal muscle tissues for regulating muscle contraction. Actin, a globular contractile protein, interacts with myosin for muscle contraction. The skeletal tissue appears striped or striated under a microscope due to the repeated arrangement of contractile proteins actin and myosin along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes...
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The Quantification of Injectability by Mechanical Testing
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Structural dynamics of contractile injection systems.

Noah Toyonaga1, L Mahadevan2

  • 1Department of Physics, Harvard University, Cambridge, Massachusetts.

Biophysical Journal
|November 24, 2024
PubMed
Summary
This summary is machine-generated.

We developed a coarse-grained model for contractile injection systems (CISs) to understand their contraction dynamics. Our model predicts the size, shape, and speed of the contraction front, offering insights into macromolecular machine function.

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Area of Science:

  • Biophysics
  • Structural Biology
  • Computational Biology

Background:

  • Macromolecular machines undergo chemically mediated structural changes for function.
  • Contractile injection systems (CISs) are a class of such machines.
  • High-resolution structural microscopy provides insights into CISs.

Purpose of the Study:

  • To construct a coarse-grained semianalytical model for CISs.
  • To recapitulate CIS geometry and bistability using physical parameters.
  • To predict the dynamics of the contraction actuation front.

Main Methods:

  • Developed a coarse-grained semianalytical model.
  • Incorporated measurable physical parameters.
  • Performed numerical simulations.

Main Results:

  • The model recapitulates CIS geometry and bistability.
  • Predicted size, shape, and speed of the contraction front.
  • Derived scaling laws for contraction front velocity and extension.

Conclusions:

  • The model provides a minimal parameter framework for CIS dynamics.
  • Scaling laws are consistent with simulations and may apply to related systems.
  • The study advances understanding of macromolecular machine actuation.