Effects of tubulin acetylation and tubulin acetyltransferase binding on microtubule structure

Abstract

Acetylation of α-tubulin is uniquely located on the microtubule lumen and away from most MAPs. It does not affect microtubule structure and must affect only proteins that bind directly to the lumen. αTAT1 can interact with the tubulin C-termini, which could facilitate access to its luminal site and make it responsive to other modifications.

Mechanism of microtubule lumen entry for the α-tubulin acetyltransferase enzyme αTAT1

“…This result is in contrast to recent work by Szyk et al (18), which suggested that luminal αTAT1 was able to scan the length of the microtubule quickly. However, although our experimental prewashout measurements for the diffusion coefficient of αTAT1 on the microtubule lattice were similar to the prewashout measurements reported by Szyk et al (18), αTAT1 has been reported to interact electrostatically with the outside of the microtubule lattice (16), and so we surmised that our prewashout diffusion coefficient largely reflected αTAT1 diffusion on the outside of the microtubule. This argument is consistent with our observations of diffusing αTAT1-GFP molecules "jumping" from one microtubule to another on the exterior surface of the microtubule in the prewashout movies (Fig.…”

“…To test this prediction, we noted that it has been previously demonstrated that the binding affinity of αTAT1 for microtubules is suppressed at higher salt concentrations (16). Therefore, if the slow mobility of αTAT1 inside of the microtubule lumen is due to rapid high-affinity binding to densely packed tubulin subunits, we predicted that by adding salt during αTAT1 incubation, a net decrease in αTAT1 affinity for the microtubule could lead to longer acetylation patch lengths.…”

“…This finding suggests that the microtubules were broken into smaller fragments and/or damaged by successive cycles of shearing, which generated new microtubule ends and/or openings in the lattice during each cycle, and thus allowed for more acetylated microtubule ends and/or lattice openings. The increase in acetylated microtubule ends then led to a higher bulk acetylation level (16). Thus, microtubule acetylation may be facilitated by increased numbers of microtubule ends or new lattice openings.…”

“…However, despite identification of the enzyme and its substrate, the mechanism for how αTAT1 enters the microtubule lumen to access its acetylation sites is yet to be fully understood. There are several potential mechanisms for how αTAT1 may access the acetylation site on the inside of the microtubule lumen: by copolymerization with tubulin at growing microtubule plus-ends (15), by transient openings in the lattice during microtubule breathing (13,16,17), or by microtubule end-entry (12,18). Copolymerization is not likely to be the primary mechanism for αTAT1 access, because stable microtubules are acetylated, and because αTAT1 is more active on polymerized microtubules than on free tubulin dimers (12,13,(19)(20)(21)(22)(23)(24)(25).…”

Role of Signal-Regulated Changes in Microtubule Stability Dynamics through <i>α</i>-Tubulin Phosphorylation on Ser/Tyr in Modulation of Salivary Gland Matrix Metalloproteinase-9 (MMP-9) Secretion in Response to <i>Porphyromonas gingivalis</i> and Ghrelin

“…The MTs polymers, assembled from heterodimers of α-and β-tubulin proteins in a head-to-tail manner, form a dense network of filamentous tubes that undergo frequent alternating periods of growth (polymerization) and shortening (depolymerization) termed "dynamic instability" [18] [19]. The diverse aspects of MT dynamics arise from accumulation of a variety of posttranslational modifications on the tubulin subunits, including acetylation, detyrosination, polyglutamylation, polyglycylation and phosphorylation, and are further tuned and refined through binding of MT-associated proteins [19] [20] [21] [22]. Indeed, changes in MT stability dynamics and the increase in α-tubulin acetylation have been directly linked to the increase in MMP-9 secretion elicited by MT stabilizing agents [17], and we have demonstrated previously that MT destabilizing agents that inhibit microtubule polymerization exert the inhibitory effect on the increase in salivary gland acinar cell MMP-9 secretion elicited by P. gingivalis LPS [23].…”