Comments on: Molecular basis for age-dependent microtubule acetylation by tubulin acetyltransferase.

I provided some comments on this paper for F1000 Prime.

Molecular basis for age-dependent microtubule acetylation by tubulin acetyltransferase.

Szyk A, Deaconescu AM, Spector J, Goodman B … Ziolkowska NE, Kormendi V, Grigorieff N, Roll-Mecak A.  (2014) Cell  157(6):1405-15 PMID: 24906155 DOI: 10.1016/j.cell.2014.03.061

This paper combines structural biology and biochemical assays to define a mechanism by which tubulin acetyl transferase (TAT) acts almost exclusively on stable microtubules. In some ways this is a very simple paper with clear and defined outcomes. X-ray crystallography shows that the catalytic site of TAT is not optimised to deprotonate the target lysine residue (Lys-40) within tubulin. Deprotonation is a prerequisite for acetylation and therefore this sub-optimal arrangement greatly decreases the catalytic rate. The authors then use some clever biochemical tricks to demonstrate the preference of TAT for assembled microtubules rather than monomeric or even dimeric tubulin. Lys-40 lies on the inside of assembled microtubule filaments, potentially posing an accessibility problem. A clever experiment was done to show that TAT does indeed enter the lumen of the microtubule. TAT conjugated to a large diameter (1 micron) bead was not capable of acetylating microtubules. This is the clearest evidence yet that acetylation occurs within the microtubule lumen. Live imaging of GFP-TAT showed that it diffuses freely within the lumen of microtubules and acts stochastically in acetylating the length of the assembled microtubule structure. Thus, entry and diffusion of TAT into the microtubule are not limiting factors in microtubule acetylation — that limit is defined by the slow catalytic rate of the TAT enzyme itself.

The work has broad-reaching implications since acetylated microtubules have been shown to be preferred by kinesin-1 motor {1} and that the microtubules that make up the axonemes of cilia and flagella are heavily acetylated {2}.

A nice commentary accompanies this article; it contains a nice model explaining the concepts and is also worth reading {3}.

References

1.
Microtubule acetylation promotes kinesin-1 binding and transport.

Reed NA, Cai D, Blasius TL, Jih GT, Meyhofer E, Gaertig J, Verhey KJ. Curr Biol 2006 Nov 7; 16(21):2166-72

2.
Monoclonal antibodies specific for an acetylated form of alpha-tubulin recognize the antigen in cilia and flagella from a variety of organisms.

Piperno G, Fuller MT. J Cell Biol 1985 Dec; 101(6):2085-94

PMID: 2415535
3.
A Slow Dance for Microtubule Acetylation.

Kull FJ, Sloboda RD. Cell 2014 Jun 5; 157(6):1255-1256

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