Tubulin isoform composition tunes microtubule dynamics

Area of Science:

• Cell Biology
• Biochemistry
• Structural Biology

Background:

• Microtubules are crucial cytoskeletal polymers involved in cell division, motility, and differentiation.
• Microtubule dynamics are regulated by microtubule-associated proteins, but the role of tubulin genetic diversity remains less understood.
• Existing in vitro studies often use brain-derived tubulin, which may not reflect the composition in other cell types.

Purpose of the Study:

• To investigate the in vitro dynamics and structure of microtubules assembled from tubulin isoforms found in human embryonic kidney cells.
• To compare the dynamics of these non-neuronal microtubules with those derived from brain tissue.
• To explore how specific tubulin isotypes, like α1A/βIII, affect microtubule dynamics.

Main Methods:

• Purification of tubulin from a human embryonic kidney cell line.
• Assembly of α1B/βI+βIVb microtubules and analysis of their in vitro dynamics.
• 4.2-Å cryo-electron microscopy (cryo-EM) to determine microtubule structure.
• Analysis of EB1 protein distribution at microtubule dynamic ends.
• In vitro reconstitution experiments with recombinant α1A/βIII tubulin.

Main Results:

• Microtubules assembled from kidney cell tubulin (α1B/βI+βIVb) exhibit faster growth and reduced depolymerization frequency compared to brain microtubules.
• Cryo-EM revealed that the dynamic ends of α1B/βI+βIVb microtubules are less tapered with lower tubulin heterodimer curvature.
• No significant difference in GTP cap size was observed based on EB1 distribution.
• Addition of recombinant α1A/βIII tubulin proportionally modulated the dynamics of α1B/βI+βIVb microtubules.

Conclusions:

• Tubulin isoform composition significantly impacts microtubule polymerization and depolymerization dynamics.
• Non-neuronal tubulin isoforms, such as those in kidney cells, display distinct dynamic properties compared to brain tubulin.
• Understanding tubulin isoform diversity is essential for comprehending microtubule function in various cell types and disease states, including cancer.