Assembly and Colchicine Binding Characteristics of Tubulin with Maximally Tyrosinated and Detyrosinated α-Tubulins

The posttranslational removal and readdition of tyrosine at the C-terminus of α-tubulin is associated with generation of microtubule populations that differ in intracellular distributions, turnover rates, and sensitivities to microtubule-depolymerization agents. Here, we compared thein vitroassembly and colchicine binding characteristics of tubulin dimer preparations composed of α-tubulin that had been maximally tyrosinated (∼40% tyrosinated) by tubulin-tyrosine ligase and maximally detyrosinated (100% detyrosinated) by carboxypeptidase A. Maximally tyrosinated and detyrosinated tubulins had similar critical concentrations for polymerization and similar association constants for colchicine binding. Microtubules polymerized from the two tubulins also had similar steady-state mean lengths and length distributions. The growing and shortening dynamics (dynamic instability parameters) of individual microtubules made from maximally tyrosinated or detyrosinated α-tubulin as determined by video-enhanced dark-field microscopy were similar, but subtle differences in the growing and shortening rates were found. On balance, however, the dynamicity and thus the overall kinetic stability of the two microtubule populations were indistinguishable. The results support the idea that detyrosination of α-tubulin does not by itself generate stable microtubules.