The name is absent

Removal of the penultimate glutamate residue from the α-tubulin polypeptide
produces ∆2-tubulin, a derivative that is unable to act as a substrate for tubulin-
tyrosine ligase, and this truncated protein is therefore removed from the
tyrosination cycle. ∆2-tubulin is particularly prevalent on microtubular structures
such as the axonemes of flagella and cilia and also in mammalian brain cell
microtubules.

II. Polyglutamylation and polyglycylation of both α- and β-tubulin

The tubulin modifications polyglutamylation and polyglycylation involve the
attachment of oligoglutamyl and oligoglycyl side chains of variable length to
specific glutamate residues located near the C-terminus of both α- and β-tubulin.
These side chains can be of considerable length for instance, axonemal tubulin
of Paramecium is modified by up to 34 glycyl residues (Bre et al., 1998), and the
microtubules of Trypanosoma brucei contain 15 glutamyl residues per α-tubulin
subunit (Schneider et al., 1997). Polyglutamylation and polyglycylation are
particularly associated with stable microtubule structures such as the axonemes
of cilia and flagella.

Centriolar microtubules appear to be polyglutamylated but not polyglycylated
(Million et al., 1999). Polyglutamylation appears to be critical for the stability of
centriole microtubules, since microinjection of monoclonal antibodies specific for
polyglutamylated tubulin isotypes, results in the transient disappearance of
centrioles in mammalian cells (Bobbinec et al., 1998).

Polyglutamylation also represents the major post-translational modification of
axonal tubulin in neuronal cells, where it appears to regulate the differential
interaction between microtubules and microtubule-associated proteins (MAPs).
For instance, MAPs such as tau and kinesin exhibit optimal binding to tubulin

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