Molecular investigations into the unfoldase action of severing enzymes on microtubules

Area of Science:

• Biochemistry
• Cell Biology
• Biophysics

Background:

• Microtubule (MT)-associated proteins regulate MT dynamics.
• MT severing enzymes destabilize MTs by removing tubulin subunits.
• Severing enzymes are AAA+ unfoldases, suggesting a potential unfolding mechanism.

Purpose of the Study:

• To investigate the mechanism by which MT severing enzymes remove tubulin dimers.
• To test the hypothesis that severing enzymes unfold MT subunits by pulling on carboxy-terminal tails.

Main Methods:

• Coarse-grained molecular simulations applying pulling forces on MT subunit carboxy-terminal regions.
• Simulations used varying MT lattices and severing enzyme concentrations.
• Comparison of simulation results with in vitro severing assay data.

Main Results:

• The experimental data is best explained by a model of cooperative protofilament fragment removal.
• This cooperative removal is dependent on severing enzyme concentration.
• Severing enzyme placement on the MT lattice also influences the removal process.

Conclusions:

• The findings support a model of cooperative fragment removal rather than simple unfolding of individual subunits.
• Severing enzyme concentration and lattice placement are critical factors in MT destabilization.
• This study provides insights into the mechanical mechanisms of microtubule regulation.