Myosin subfragment 1 activates ATP hydrolysis on Mg(2+)-G-actin

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Myosin-Specific Adaptations of In vitro Fluorescence Microscopy-Based Motility Assays
08:57

Myosin-Specific Adaptations of In vitro Fluorescence Microscopy-Based Motility Assays

Published on: February 4, 2021

A A Kasprzak1

  • 1Centre de Recherches de Biochimie Macromoléculaire, CNRS-INSERM U. 249, Université de Montpellier I, France.

Biochemistry
|October 18, 1994
PubMed

Insights

Myosin subfragment 1 isoenzyme A2 (S1A2) forms a tight complex with Mg(2+)-G-actin, accelerating ATP hydrolysis. This interaction is specific for Mg(2+)-G-actin, not Ca(2+)-G-actin.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Muscle Contraction

Background:

  • Actin and myosin are key proteins in muscle contraction.
  • Understanding their interaction is crucial for elucidating muscle function.
  • Myosin subfragment 1 (S1) is a functional unit of myosin that binds actin.

Purpose of the Study:

  • To investigate the interaction between myosin subfragment 1 isoenzyme A2 (S1A2) and Mg(2+)-G-actin.
  • To determine the effect of S1A2 on nucleotide and metal ion binding and hydrolysis kinetics.
  • To explore the specificity of this interaction regarding different actin-metal complexes.

Main Methods:

  • Polarization titrations using fluorescently labeled actin (1,5-IAEDANS-Mg(2+)-G-actin and epsilon ATP-Mg(2+)-G-actin) with S1A2.
  • Measurement of nucleotide and metal dissociation rates.
  • Quantification of ATP hydrolysis rates using radiolabeled ATP and alkaline phosphatase.

Main Results:

  • S1A2 forms a tight binary complex with Mg(2+)-G-actin, similar to Ca(2+)-G-actin.
  • Actin's ATP hydrolysis rate within the S1A2 complex is significantly faster than nucleotide dissociation.
  • S1A2 accelerates ATP dissociation but inhibits ADP dissociation, indicating hydrolysis precedes release.
  • The ATPase activation by S1A2 is specific to Mg(2+)-G-actin and absent in Ca(2+)-G-actin.

Conclusions:

  • Myosin subfragment 1 isoenzyme A2 (S1A2) forms a stable complex with Mg(2+)-G-actin, facilitating ATP hydrolysis.
  • The hydrolysis of ATP by actin is a key step in the actin-myosin interaction cycle.
  • The observed specificity for Mg(2+)-G-actin highlights the distinct roles of divalent cations in actin-myosin dynamics.

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