Competitive Microtubule Binding of PEX14 Coordinates Peroxisomal Protein Import and Motility

PEX14 functions as peroxisomal docking protein for the import receptor PEX5. For docking, the conserved N-terminal domain of PEX14 (PEX14-NTD) binds amphipathic alpha-helical ligands, typically comprising one or two aromatic residues, of which human PEX5 possesses eight. Here, we show that the PEX14-NTD also binds to microtubular filaments in vitro with a dissociation constant in nanomolar range. PEX14 interacts with two motifs in the C-terminal region of human {beta}-tubulin. At least one of the binding motifs is in spatial proximity to the binding site of microtubules (MT) for kinesin. Both PEX14 and kinesin can bind to MT simultaneously. Notably, binding of PEX14 to tubulin can be prevented by its association with PEX5. The data suggest that PEX5 competes peroxisome anchoring to MT by occupying the {beta}-tubulin-binding site of PEX14. The competitive correlation of matrix protein import and motility may facilitate the homogeneous dispersion of peroxisomes in mammalian cells.