Beta3 accelerates microtubule plus end maturation through a divergent lateral interface

Abstract

{beta}-tubulin isotypes exhibit similar sequences but different activities, suggesting that limited sequence divergence is functionally important. We investigated this hypothesis for TUBB3/{beta}3, a {beta}-tubulin linked to aggressive cancers and chemoresistance in humans. We created mutant yeast strains with {beta}-tubulin alleles that mimic variant residues in {beta}3 and find that residues at the lateral interface are sufficient to alter microtubule dynamics and response to microtubule targeting agents. In HeLa cells, {beta}3 overexpression decreases the lifetime of microtubule growth, and this requires residues at the lateral interface. These microtubules exhibit a shorter region of EB binding at the plus end, suggesting faster lattice maturation, and resist stabilization by paclitaxel. Resistance requires the H1-S2 and H2-S3 regions at the lateral interface of {beta}3. Our results identify the mechanistic origins of the unique activity of {beta}3 tubulin and suggest that tubulin isotype expression may tune the rate of lattice maturation at growing microtubule plus ends in cells.