Question 1

What causes microtubules to destabilize?

Accepted Answer

Microtubules destabilize when the rate of catastrophe, or shortening, exceeds the rate of rescue, or elongation. This imbalance can be triggered by microtubule-associated proteins like stathmin and kinesin-13, which actively promote tubulin subunit detachment. Temperature and critical concentration of free tubulin heterodimers also influence destabilization rates.

Question 2

How does stathmin destabilize microtubules?

Accepted Answer

Stathmin destabilizes microtubules through two mechanisms. In the cytoplasmic pool, it sequesters tubulin heterodimers by binding to them and altering their conformation, preventing assembly onto microtubules. Additionally, stathmin binds to microtubule tips and bends the filaments, sequentially removing tubulin subunits and shifting the balance from elongation to shrinkage.

Question 3

What is the role of kinesin-13 in microtubule destabilization?

Accepted Answer

Kinesin-13 is a non-motile ATP-dependent destabilizer that binds at microtubule tips and promotes conversion of GTP-beta-tubulin to GDP-beta-tubulin. This conversion lowers the heterodimer's affinity for adjacent subunits, causing easy release of tubulin dimers. ATP hydrolysis then separates kinesin-13 from the detached subunit.

Question 4

How does temperature affect microtubule destabilization?

Accepted Answer

Temperature significantly influences microtubule destabilization rates. In vitro studies show that microtubules disassemble faster at 4°C while rapidly reassembling at 37°C. This temperature sensitivity reflects the dynamic nature of tubulin polymerization and the energy-dependent processes controlling microtubule stability and assembly.

Question 5

What is critical concentration and how does it relate to microtubule destabilization?

Accepted Answer

Critical concentration (Cc) is the concentration of free αβ-tubulin heterodimers at which net polymerization equals zero. Microtubule destabilization occurs when heterodimer concentration falls below the Cc. During the cell cycle, cells transition between catastrophe and rescue depending on whether tubulin concentration is above or below this critical threshold.

Question 6

How do microtubule lifespans vary across different cell types?

Accepted Answer

Microtubule lifespan varies significantly by cell type and cell cycle stage. During interphase, microtubules typically persist for about 30 minutes, while during cell division they last approximately 15 minutes. In specialized structures like axonal microtubules in neurons or axonemes in cilia and flagella, microtubules have considerably longer lifespans.

Question 7

What role does katanin play in microtubule destabilization?

Accepted Answer

Katanin is a microtubule destabilizer with two subunits that sever longitudinal bonds between protofilaments, causing rapid destabilization. During cell division, katanin detaches microtubules from centrosomes, destabilizing spindle fibers. Its destabilizing activity also occurs during interphase in proliferating cells, contributing to dynamic microtubule remodeling and the movement of organelles and vesicles.

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