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Macromolecular Crowding Modulates Actomyosin Kinetics.

Jinghua Ge1, Sherry D Bouriyaphone2, Tamara A Serebrennikova3

  • 1Department of Physics and Optical Science, University of North Carolina, Charlotte, North Carolina; Center for Biomedical Engineering and Science, University of North Carolina, Charlotte, North Carolina.

Biophysical Journal
|July 14, 2016
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Summary

Cellular crowding affects actomyosin kinetics. Macromolecular crowding, using Ficoll70, increased actomyosin ATPase cycle velocity and altered individual reaction steps, suggesting conformational changes in myosin.

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Area of Science:

  • Biochemistry
  • Cell Biology
  • Biophysics

Background:

  • Actomyosin kinetics are typically studied in dilute solutions, not reflecting cellular environments.
  • Cellular cytoplasm is a crowded macromolecular space influencing protein behavior.
  • Macromolecular crowding affects solute chemical potential and protein stabilization.

Purpose of the Study:

  • To investigate the impact of macromolecular crowding on actomyosin ATPase cycle kinetics.
  • To determine how crowding modulates individual steps within the actomyosin cycle.
  • To elucidate the mechanisms behind crowding-induced changes in actomyosin function.

Main Methods:

  • Studied actomyosin cycle reactions in the presence of Ficoll70 to emulate cellular crowding.
  • Utilized transient-kinetics experiments to analyze individual reaction steps.
  • Employed time-resolved Förster resonance energy transfer (FRET) to assess myosin head conformation.

Main Results:

  • Observed an increase in the maximum velocity of the actomyosin ATPase cycle with Ficoll70.
  • Transient-kinetics revealed alterations in virtually all individual steps of the actomyosin cycle.
  • FRET experiments confirmed a more compact myosin head conformation in crowded conditions.

Conclusions:

  • Macromolecular crowding significantly modulates actomyosin ATPase kinetics.
  • Crowding-induced conformational changes in the myosin head are a key factor in altered kinetics.
  • The effects observed cannot be solely explained by increased solute chemical potential.