β3 accelerates microtubule plus end maturation through a divergent lateral interface.

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Beta-tubulin isotypes share sequence similarity but possess distinct biological activities.
• The beta-tubulin isotype TUBB3 (β3) is implicated in aggressive cancers and chemoresistance.
• Functional divergence despite sequence similarity suggests critical roles for specific residues.

Purpose of the Study:

• To investigate the functional importance of limited sequence divergence in beta-tubulin isotypes.
• To elucidate the mechanistic basis for the unique activity of TUBB3/β3.
• To determine how TUBB3/β3 influences microtubule dynamics and response to chemotherapy.

Main Methods:

• Created mutant yeast strains expressing beta-tubulin alleles mimicking TUBB3 variant residues.
• Utilized HeLa cells to study the effects of β3 overexpression on microtubule dynamics.
• Analyzed microtubule growth, EB binding, and response to paclitaxel in wild-type and mutant cells.

Main Results:

• Residues at the lateral interface of β3 are sufficient to modify microtubule dynamics and response to microtubule-targeting agents.
• Overexpression of β3 in HeLa cells reduces microtubule growth lifetime, dependent on lateral interface residues.
• Microtubules with β3 show faster lattice maturation and resistance to paclitaxel, requiring specific lateral interface regions (H1-S2 and H2-S3).

Conclusions:

• Identified specific residues at the lateral interface of β3 as key determinants of its unique functional activity.
• Demonstrated that β3 tubulin influences microtubule lattice maturation rate at the growing plus end.
• Suggests that differential tubulin isotype expression can modulate cellular responses to microtubule-targeting drugs.