STRUCTURE OF THE C-TERMINAL TAIL OF ALPHA-TUBULIN - INCREASE OF HETEROGENEITY FROM NEWBORN TO ADULT

A combination of posttranslational modifications contributes to the hi gh heterogeneity of brain tubulin in mammals. In this report, the stru ctures of the detyrosinated carboxy-terminal peptides of alpha-tubulin from newborn and adult mouse brain were compared. The heterogeneity o f these carboxy-terminal peptides was observed to increase from newbor n to adult brain tubulin. The major part of this increased heterogenei ty is due to the post-translational excision of Glu(450), which makes alpha-tubulin nontyrosinatable (Delta-2 tubulin). The structures of th e polyglutamyl side chain of the bi- and triglutamylated peptides were analyzed in this work. In polyglutamylation of alpha-tubulin, the fir st glutamyl residue can only be amide-linked to the gamma-carboxyl gro up of Glu(445), but the additional residues may be linked either to th e gamma- or to the alpha-carboxyl groups of the preceding one. By opti mized reverse-phase separations and comparison with synthetic peptides corresponding to all possible linkages for the biglutamylated (gamma 1 alpha 2, gamma 2 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 add itional glutamyl residues corresponds mostly to alpha-bond structures, for both newborn and adult mice.