Microtubules are structural polymers inside of cells that are subject to posttranslational modifications. These posttranslational modifications create functionally distinct subsets of microtubule networks in the cell, and acetylation is the only modification that takes place in the hollow lumen of the microtubule. Although it is known that the α-tubulin acetyltransferase (αTAT1) is the primary enzyme responsible for microtubule acetylation, the mechanism for how αTAT1 enters the microtubule lumen to access its acetylation sites is not well understood. By performing biochemical assays, fluorescence and electron microscopy experiments, and computational simulations, we found that αTAT1 enters the microtubule lumen through the microtubule ends, and through bends or breaks in the lattice. Thus, microtubule structure is an important determinant in the acetylation process. In addition, once αTAT1 enters the microtubule lumen, the mobility of αTAT1 within the lumen is controlled by the affinity of αTAT1 for its acetylation sites, due to the rapid rebinding of αTAT1 onto highly concentrated α-tubulin acetylation sites. These results have important implications for how acetylation could gradually accumulate on stable subsets of microtubules inside of the cell.
