Tubulin acetylation protects long-lived microtubules against mechanical ageing

Abstract

Introductory ParagraphLong-lived microtubules endow the eukaryotic cell with long-range transport abilities. While long-lived microtubules are acetylated on lysine 40 of α-tubulin (αK40), acetylation takes place after stabilization1 and does not protect against depolymerization2. Instead, αK40 acetylation has been proposed to mechanically stabilize microtubules3. Yet how modification of αK40, a residue exposed to the microtubule lumen and inaccessible from MAPs and motors1,4, could affect microtubule mechanics remains an open question. Here we develop FRET-based assays that report on the lateral interactions between protofilaments and find that αK40 acetylation directly weakens inter-protofilament interactions. Congruently, αK40 acetylation affects two processes largely governed by inter-protofilament interactions, reducing the nucleation frequency and accelerating the shrinkage rate. Most relevant to the biological function of acetylation, microfluidics manipulations demonstrate that αK40 acetylation enhances flexibility and confers resilience against repeated mechanical stresses. Thus, unlike deacetylated microtubules that accumulate damages when subjected to repeated stresses, long-lived microtubules are protected from mechanical aging through their acquisition of αK40 acetylation. Thus, unlike other tubulin post-translational modifications that act through MAPs, motors and severing enzymes, intraluminal acetylation directly tunes the compliance and resilience of microtubules.

Microtubule Acetylation Is Required for Mechanosensation in Drosophila

“…Instead, we observed an increase in EB1-labeled microtubule plus ends in dTat mutant sensory dendrites and showed that stabilizing the cytoskeleton by feeding mutant animals taxol rescued touch sensitivity. In light of recent findings that K40 acetylation weakened inter-protofilament interactions, allowing microtubules to comply with deformative forces without breaking (Portran et al, 2017; Xu et al, 2017), our results suggest that in the absence of K40 acetylation, microtubules in c3da neurons are mechanically damaged, thereby decreasing NOMPC-microtubule interactions and attenuating the channel’s ability to transduce mechanical stimuli. We cannot exclude the possibility that regulation of microtubule dynamics is a major functional role for acetylation in PNS neurons; further investigation into the influence of microtubule structure and dynamics on NOMPC-microtubule interactions should help resolve whether acetylation controls mechanosensation primarily via the regulation of microtubule mechanical resilience or dynamics.…”

“…Recent reports have established a role for acTb in regulating microtubule dynamics and in conferring microtubules with resistance to mechanical breakage (Portran et al, 2017; Xu et al, 2017). Because NOMPC interacts with microtubules via its AR domain and this interaction is required for mechanosensation (Cheng et al, 2010; Zhang et al, 2015), we speculated that loss of dTat would perturb the mechanical properties of microtubules and/or microtubule dynamics to inhibit mechanosensation.…”

“…α-Tubulin acetylation occurs on lysine 40 (K40) in the microtubule lumen and has generally been associated with populations of long-lived microtubules. Recent studies in which individual microtubules were mechanically stressed by repeated cycles of bending showed that they could be damaged, resulting in decreased microtubule stiffness and localized material fatigue (Portran et al, 2017). K40 acetylation enhanced microtubule flexibility and increased mechanical resilience by altering the lattice structure, allowing microtubules to comply with deformative forces without breaking (Xu et al, 2017) and suggesting that α-tubulin acetylation regulates the mechanical resilience of microtubules.…”

Microtubules acquire resistance from mechanical breakage through intralumenal acetylation

“…While detyrosination alters the binding site for microtubule associated proteins (MAPs), severing enzymes and motors to create specialized microtubule tracks (2), the molecular consequences of αK40 acetylation remain elusive and it is difficult to conceptualize how the modification of a residue inaccessible from outside the microtubule could alter MAP and motor binding (2, 3). We recently proposed that acetylation modifies microtubule mechanics by weakening interprotofilament interactions (4)…”

“…Because microtubules are very stiff polymers that rupture when subjected to flexural stresses (13), this highly bent morphology suggests the existence of protective mechanisms for long-lived microtubules. The repair of lattice defects has emerged as an intrinsic property of microtubules that are subjected to mechanical stress (14, 15) and acetylation protects microtubule from mechanical fatigue in vitro (4). Further suggesting that acetylation may confer mechanical protection to microtubules, removing TAT-1 from touch receptor neurons of nematodes results in profound microtubule lattice defects (6, 16) that can be rescued by paralyzing the animals (8).…”