tubulin

Tubulin refers to a family of globular proteins that assemble into microtubules, the dynamic filaments of the cytoskeleton. In most cells the functional units are alpha- and beta-tubulin subunits that form heterodimers around 100 kDa. Each subunit is about 50 kDa and binds guanine nucleotides; beta-tubulin's GTP is hydrolyzed after incorporation into microtubules, while alpha-tubulin binds GTP in a non-exchangeable manner. Gamma-tubulin, a related protein, nucleates microtubule assembly at microtubule organizing centers.

Microtubules are polar polymers that grow and shrink through tubulin addition and loss—a behavior termed dynamic instability. This enables spindle formation during mitosis, intracellular transport by motor proteins, and the organization of the cytoplasm. Microtubule nucleation commonly occurs at centrosomes via the gamma-tubulin ring complex; cilia and flagella contain stable microtubule arrays built on similar principles.

The tubulin family includes multiple alpha- and beta-tubulin isotypes encoded by several genes with tissue-specific expression. Tubulin folding involves chaperones that guide newly synthesized polypeptides to functional heterodimers. Tubulins are subject to post-translational modifications such as acetylation, detyrosination, and polyglutamylation, which influence microtubule stability and interactions with MAPs and motor proteins.

In medicine, microtubules are targeted by anticancer drugs that stabilize or destabilize them, interfering with cell division. Abnormal tubulin expression or mutations are linked to neurodevelopmental disorders and other diseases, making tubulin dynamics an area of active research.