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Structure of the C-terminal tail of alpha-tubulin: increase of heterogeneity from newborn to adult.

A combination of posttranslational modifications contributes to the high heterogeneity of brain tubulin in mammals. In this report, the structures of the detyrosinated carboxy-terminal peptides of alpha-tubulin from newborn and adult mouse brain were compared. The heterogeneity of these carboxy-terminal peptides was observed to increase from newborn to adult brain tubulin. The major part of this increased heterogeneity is due to the post-translational excision of Glu450, which makes alpha-tubulin nontyrosinatable (delta-2 tubulin). The structures of the polyglutamyl side chain of the bi- and triglutamylated peptides were analyzed in this work. In polyglutamylation of alpha-tubulin, the first glutamyl residue can only be amide-linked to the gamma-carboxyl group of Glu445, but the additional residues may be linked either to the gamma- or to the alpha-carboxyl groups of the preceding one. By optimized reverse-phase separations and comparison with synthetic peptides corresponding to all possible linkages for the biglutamylated (gamma 1 alpha 2, gamma 1 gamma 2) and triglutamylated (gamma 1 alpha 2 alpha 3, gamma 1 gamma 2 gamma 3, gamma 1 alpha 2 gamma 3, gamma 1 gamma 2 alpha 3, gamma 1 gamma 2 alpha 2) tubulin peptides, it was possible to conclude that the mode of linkage connecting the second and third additional glutamyl residues corresponds mostly to alpha-bond structures, for both newborn and adult mice.