Among the different types of cytoskeletal components, microtubules arguably accumulate the greatest diversity of post-translational modifications (PTMs). Acetylation of lysine 40 (K40) of α-tubulin has received particular attention because it is the only tubulin PTM to be found in the lumen of microtubules: most other tubulin PTMs are found at the outer surface of the microtubule. As a consequence, the enzyme catalyzing K40 acetylation needs to penetrate the narrow microtubule lumen to find its substrate. Acetylated microtubules have been considered to be stable, long-lived microtubules; however, until recently, there was little information about whether the longevity of these microtubules is the cause or the consequence of acetylation. Current advances suggest that this PTM helps the microtubule lattice to cope with mechanical stress, thus facilitating microtubule self-repair. These observations now shed new light on the structural integrity of microtubules, as well as on the mechanisms and biological functions of tubulin acetylation. Here, we discuss recent insights into how acetylation is generated in the lumen of microtubules, and how this 'hidden' PTM can control the properties and functions of microtubules.
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