Tubulin tails and their modifications regulate protein diffusion on microtubules

Abstract

Microtubules (MTs) are essential components of the eukaryotic cytoskeleton that serve as “highways” for intracellular trafficking. In addition to the well-known active transport of cargo by motor proteins, many MT-binding proteins seem to adopt diffusional motility as a transportation mechanism. However, because of the limited spatial resolution of current experimental techniques, the detailed mechanism of protein diffusion has not been elucidated. In particular, the precise role of tubulin tails and tail modifications in the diffusion process is unclear. Here, using coarse-grained molecular dynamics simulations validated against atomistic simulations, we explore the molecular mechanism of protein diffusion along MTs. We found that electrostatic interactions play a central role in protein diffusion; the disordered tubulin tails enhance affinity but slow down diffusion, and diffusion occurs in discrete steps. While diffusion along wild-type MT is performed in steps of dimeric tubulin, the removal of the tails results in a step of monomeric tubulin. We found that the energy barrier for diffusion is larger when diffusion on MTs is mediated primarily by the MT tails rather than the MT body. In addition, globular proteins (EB1 and PRC1) diffuse more slowly than an intrinsically disordered protein (Tau) on MTs. Finally, we found that polyglutamylation and polyglycylation of tubulin tails lead to slower protein diffusion along MTs, although polyglycylation leads to faster diffusion across MT protofilaments. Taken together, our results explain experimentally observed data and shed light on the roles played by disordered tubulin tails and tail modifications in the molecular mechanism of protein diffusion along MTs.

Nna1 gene deficiency triggers Purkinje neuron death by tubulin hyperglutamylation and ER dysfunction

“…Ttll3 glycylates β-tubulin tails and interacts there with the glutamylases Ttll7 and likely Ttll1 in molecular competition for binding to overlapping sites on tubulin tails, thus providing a molecular basis for an opposing correlation between increasing glutamylation and decreasing glycylation. Studies are underway to elucidate what structural elements differentiate glycylases from glutamylases, both of which share the common TTLL scaffold (e.g., 45,46).…”

Biased Brownian Motion of KIF1A and the Role of Tubulin’s C-Terminal Tail Studied by Molecular Dynamics Simulation

“…The increased binding affinity and the alteration of KIF1A's motility by polyglutamylation have actually been observed in a recent study [11]. The electrostatic effects of the polyglutamylation in the CTT can be seen for other MT-binding proteins [16,17] such as microtubule-associated proteins (MAPs) and Tau, which suggests that the polyglutamylation could regulate the axonal transport through altering the binding affinity of those MT-binding proteins that impede the motility of KIF1A [11]. Considering that KIF1A moves along the MT in the dimeric form in vivo [10], it remains unclear whether the Brownian ratchet mechanism contributes to the active transport along the MT in a cell.…”

“…In particular, the role of the CTT in biased Brownian motion has not been fully explored. Recently, the role of the CTT has attracted much attention from the viewpoint of the "tubulin code" as well [14,15]; the interaction of the CTT with MT-binding proteins, including KIF1A, is regulated by the post-translational modifications of the CTT, in particular by polyglutamylation, which strengthens the net negative charge of the CTT [16,17].…”

What Are the Molecular Requirements for Protein Sliding along DNA?

“…For example, linear diffusion of proteins along microtubules is different for intrinsically disordered proteins and globular proteins. 11 Modifying microtubules post-translationally (e.g., polyglutamylation or polyglycylation) affects the ruggedness of the energy landscape for diffusion. 11 …”

“… 11 Modifying microtubules post-translationally (e.g., polyglutamylation or polyglycylation) affects the ruggedness of the energy landscape for diffusion. 11 …”