Tubulin is the major constituent of microtubules, a cylinder consisting of laterally associated linear protofilaments composed of alpha- and beta-tubulin heterodimers. Microtubules grow by the addition of GTP-tubulin dimers to the microtubule end, where a stabilizing cap forms. Below the cap, tubulin dimers are in GDP-bound state, owing to GTPase activity of alpha-tubulin.
Subcellular locations: Cytoplasm, Cytoskeleton
Major isotype in brain, where it represents 46% of all beta-tubulins. In the brain, highest expression levels in the cerebellum, followed by putamen and white matter. Moderate levels in testis. Very low levels, if any, in other tissues.