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

Area of Science:

• Biochemistry
• Cell Biology
• Structural Biology

Background:

• Microtubule dynamics are crucial for cellular processes.
• The role of nucleotide-bound tubulin (GTP- or GDP-tubulin) in regulating microtubule interaction strength is debated.
• Two models exist: 'self-acting' (cis) and 'interface-acting' (trans).

Purpose of the Study:

• To differentiate between the 'self-acting' and 'interface-acting' models of nucleotide influence on tubulin interactions.
• To elucidate the precise mechanism by which nucleotide state affects microtubule dynamics.

Main Methods:

• Mixed nucleotide simulations of microtubule elongation.
• Experimental measurement of microtubule plus- and minus-end elongation rates using mixed nucleotides.
• Comparison of simulation predictions with experimental data.

Main Results:

• Simulations predicted distinct growth rate changes for 'self-acting' vs. 'interface-acting' models under mixed nucleotide conditions.
• Experimental results showed a disproportionate decrease in plus-end growth rates with increasing GDP-tubulin, supporting the 'interface-acting' model.
• GDP-tubulin was found to 'poison' plus-ends but not minus-ends, with nucleotide exchange mitigating this effect at plus-ends.

Conclusions:

• The interfacial nucleotide, not the self-bound nucleotide, determines tubulin:tubulin interaction strength.
• This study resolves the debate regarding the influence of nucleotide state on microtubule dynamics.
• Findings highlight the importance of the nucleotide at the dimer interface for microtubule stability and growth.