Association of brain γ-tubulins with αβ-tubulin dimers

Abstract

γ-Tubulin is necessary for nucleation and polar orientation of microtubules in vivo. The molecular mechanism of microtubule nucleation by γ-tubulin and the regulation of this process are not fully understood. Here we show that there are two γ-tubulin forms in the brain that are present in complexes of various sizes. Large complexes tend to dissociate in the presence of a high salt concentration. Both γ-tubulins co-polymerized with tubulin dimers, and multiple γ-tubulin bands were identified in microtubule protein preparations under conditions of non-denaturing electrophoresis. Immunoprecipitation experiments with monoclonal antibodies against γ-tubulin and α-tubulin revealed interactions of both γ-tubulin forms with tubulin dimers, irrespective of the size of complexes. We suggest that, besides small and large γ-tubulin complexes, other molecular γ-tubulin form(s) exist in brain extracts. Two-dimensional electrophoresis revealed multiple charge variants of γ-tubulin in both brain extracts and microtubule protein preparations. Post-translational modification(s) of γ-tubulins might therefore have an important role in the regulation of microtubule nucleation in neuronal cells.