Binds to the plus end of microtubules and regulates the dynamics of the microtubule cytoskeleton. Promotes microtubule growth and microtubule bundling. Links cytoplasmic vesicles to microtubules and thereby plays an important role in intracellular vesicle trafficking. Plays a role macropinocytosis and endosome trafficking. Localizes to microtubule plus ends. Localizes preferentially to the ends of tyrosinated microtubules. Accumulates in plasma membrane regions with ruffling and protrusions. Associates with the membranes of intermediate macropinocytic vesicles. Additional isoforms seem to exist. Intramolecular interaction between the zinc finger domain and the CAP-Gly domains may inhibit interaction with tubulin.