An ensemble of specifically targeted proteins stabilizes cortical microtubules in the human parasite Toxoplasma gondii.

Although all microtubules within a single cell are polymerized from virtually identical subunits, different microtubule populations carry out specialized and diverse functions, including directional transport, force generation, and cellular morphogenesis. Functional differentiation requires specific targeting of associated proteins to subsets or even subregions of these polymers. The cytoskeleton of Toxoplasma gondii, an important human parasite, contains at least five distinct tubulin-based structures. In this work, we define the differential localization of proteins along the cortical microtubules of T. gondii, established during daughter biogenesis and regulated by protein expression and exchange. These proteins distinguish cortical from mitotic spindle microtubules, even though the assembly of these subsets is contemporaneous during cell division. Finally, proteins associated with cortical microtubules collectively protect the stability of the polymers with a remarkable degree of functional redundancy.