Reversible polyglutamylation of alpha- and beta-tubulin and microtubule dynamics in mouse brain neurons.

Abstract

The relationship between microtubule dynamics and polyglutamylation of [3H]glutamate into a-and 3-tubulin, whereas taxol had no effect for a-tubulin and a stimulating effect for f-tubulin. These results strongly suggest that microtubule polymers are the preferred substrate for polyglutamylation. Chase experiments revealed the existence of a reversal reaction that, in the case of a-tubulin, was not affected by microtubule drugs, suggesting that deglutamylation of this subunit can occur on both polymers and soluble tubulin. Evidence was obtained that deglutamylation of a-tubulin operates following two distinct rates depending on the length of the polyglutamyl chain, the distal units (4th-6th) being removed rapidly whereas the proximal ones (lst-3rd) appearing much more resistant to deglutamylation. Partition of glutamylated a-tubulin isoforms was also correlated with the length of the polyglutamyl chain. Forms bearing four to six units were recovered specifically in the polymeric fraction, whereas those bearing one to three units were distributed evenly between polymeric and soluble fractions. It thus appears that the slow rate component of the deglutamylation reaction offers to neurons the possibility to maintain a basal level of glutamylated a-tubulin in the soluble pool independently of microtubule dynamics. Finally, some differences observed in the glutamylation of a-and ,B-tubulin suggest that distinct enzymes are involved.

Alterations in the balance of tubulin glycylation and glutamylation in photoreceptors leads to retinal degeneration

“…The bestcharacterized PTMs of tubulin are acetylation (of lysine 40 of α-tubulin; L' Hernault and Rosenbaum, 1985;Piperno et al, 1987), enzymatic detyrosination and re-tyrosination of α-tubulin (Arce et al, 1975;Hallak et al, 1977), and the posttranslational addition of glutamate and glycine chains to both, α-and β-tubulin, referred to as polyglutamylation (Eddé et al, 1990) and polyglycylation (Redeker et al, 1994). Most of these PTMs accumulate on long-lived, functionally specialized MTs (Cambray-Deakin and Burgoyne, 1987;Schulze et al, 1987), and are consequently enriched on the axonemes of cilia and flagella (Mary et al, 1996(Mary et al, , 1997, on centrioles of the centrosome and the basal bodies (Bobinnec et al, 1998) and on neuronal MTs (Audebert et al, 1993(Audebert et al, , 1994. Despite their general abundance on stable MT assemblies, each PTM is expected to fulfil specific functions in the regulation of the MT cytoskeleton.…”

Polyglutamylation Is a Post-translational Modification with a Broad Range of Substrates

“…Polyglutamylation was initially discovered on brain ␣-tubulin and subsequently also observed on ␤-tubulin (1,5,6). It was considered as a tubulin-specific modification until it was demonstrated to target also NAP1 and NAP2 (7).…”

“…Polyglutamylation is a reversible polymodification generated by sequential covalent attachment of glutamic acids (up to 20 in some cases) to an internal glutamate residue of the target protein (1). The length of the resulting side chain is regulated by the balance between the enzymes that catalyze glutamylation, recently identified as members of the tubulin-tyrosine ligase-like (TTLL) 2 protein family (2)(3)(4), and yet unidentified deglutamylase enzymes (5). Thus, this modification does not only generate "on" and "off" states, but a range of signals that might allow for gradual regulation of protein functions.…”

Post-translational modifications of microtubules

“…In Toxoplasma gondii, a potentially polymodifiable residue of -tubulin, E434, undergoes carboxyl methylation (Xiao et al, 2010), a PTM of unknown effect, that could also compete with tubulin glutamylation (Plessmann et al, 2004). Biochemical studies have detected activities that shorten polymodification side chains: deglutamylation (Audebert et al, 1993) and deglycylation (Bre et al, 1998). A recent study identifies the carboxypeptidase CCP5 as the tubulin deglutamylase (Kimura et al, 2010).…”