betatubulin

Beta-tubulin, also written as betatubulin, is a cytosolic protein that, together with alpha-tubulin, polymerizes to form microtubules, a major component of the cytoskeleton in eukaryotic cells. It exists as several isotypes encoded by a family of TUBB genes in humans and other vertebrates. These isotypes have distinct tissue distributions and may influence microtubule properties, dynamics, and interactions with motor proteins and microtubule-associated proteins.

Structure and function: Beta-tubulin is a 50–55 kDa globular protein that binds guanine nucleotides. It forms a heterodimer with alpha-tubulin, and the α/β-tubulin dimers assemble longitudinally and laterally to create hollow microtubules. Each beta-tubulin subunit binds GTP; hydrolysis of GTP after incorporation into the microtubule regulates polymerization/depolymerization and dynamic instability. Microtubules serve as tracks for intracellular transport, help determine cell shape, organize the mitotic spindle, and form cilia or flagella in many cell types.

Isoforms and expression: In humans several beta-tubulin genes encode diverse isotypes such as those designated as β-tubulin I, II, III (neuronal), IV, and others. Beta-III tubulin (TUBB3) is widely used as a neuronal marker in research and pathology. Some isotypes are enriched in platelets, neurons, or other tissues.

Clinical and research relevance: Altered beta-tubulin expression or mutations can affect microtubule behavior and drug sensitivity. High levels of beta-III tubulin have been associated with resistance to taxane-based chemotherapy in several cancers. Mutations in beta-tubulin genes can contribute to neurodevelopmental disorders by disrupting neuronal migration and cortical development.

Regulation and modifications: Tubulin levels are regulated to maintain a balanced pool of alpha- and beta-tubulin. Beta-tubulin undergoes post-translational modifications, including detyrosination, acetylation, and polyglutamylation, which modulate interactions with microtubule-associated proteins and motor proteins.