Microtubule lattice defects facilitate spastin-mediated severing

Area of Science:

• Cell Biology
• Biochemistry
• Biophysics

Background:

• Microtubule length and organization are regulated by polymerases, depolymerases, and severing enzymes like spastin and katanin.
• Spastin hexamers bind microtubules, using ATP to depolymerize tubulin dimers and break microtubules.
• While posttranslational modifications regulate spastin, the effect of microtubule lattice defects on its severing activity is unknown.

Purpose of the Study:

• Investigate the impact of microtubule lattice defects on spastin severing activity.
• Determine if spastin preferentially binds to or is recruited by microtubule defects.

Main Methods:

• Prepared GMPCPP-stabilized microtubules with varying defect densities via polymerization conditions or annealing.
• Performed in vitro severing assays using spastin and microtubules with controlled defects.

Main Results:

• Microtubule defects accelerated the onset of spastin-mediated severing.
• Severing occurred twice as frequently at defect sites compared to normal lattice segments.
• No preferential binding of spastin to microtubule defect sites was observed.

Conclusions:

• Microtubule defects do not actively recruit spastin but passively destabilize the lattice.
• This lattice instability facilitates severing by spastin, requiring fewer tubulin subunits to be removed.
• A revised model suggests defects indirectly enhance microtubule severing efficiency.