Interface-acting nucleotide controls polymerization dynamics at microtubule plus- and minus-ends.

Area of Science:

• Cell Biology
• Biochemistry
• Biophysics

Background:

• Microtubule dynamics are crucial for cellular processes.
• The role of nucleotide-bound tubulin (GTP vs. GDP) in regulating microtubule assembly remains debated.
• Two models, 'self-acting' (cis) and 'interface-acting' (trans), propose different mechanisms for nucleotide influence.

Approach:

• Utilized mixed nucleotide simulations of microtubule elongation to differentiate between cis and trans models.
• Experimentally measured microtubule plus- and minus-end elongation rates in the presence of mixed nucleotides.
• Compared simulation predictions with experimental data to validate the proposed mechanism.

Key Points:

• GDP-tubulin disproportionately inhibited plus-end microtubule growth, supporting the 'interface-acting' model.
• Simulations indicated GDP-tubulin 'poisons' plus-ends but not minus-ends.
• Nucleotide exchange at terminal plus-end subunits was necessary to mitigate GDP-tubulin's inhibitory effect.

Conclusions:

• The nucleotide at the tubulin dimer interface, not the nucleotide within a single tubulin, dictates tubulin-tubulin interaction strength.
• This study resolves the debate regarding the mechanism by which nucleotide state influences microtubule dynamics.
• Findings provide a quantitative understanding of microtubule polymerization regulation.