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

Dimer of alpha and beta chains. A typical microtubule is a hollow water-filled tube with an outer diameter of 25 nm and an inner diameter of 15 nM. Alpha-beta heterodimers associate head-to-tail to form protofilaments running lengthwise along the microtubule wall with the beta-tubulin subunit facing the microtubule plus end conferring a structural polarity.

Microtubules usually have 13 protofilaments but different protofilament numbers can be found in some organisms and specialized cells. Component of sperm flagellar doublet microtubules (By similarity)

Expressed at a high level in fetal brain

• Lissencephaly 3 (LIS3)

  A classic type lissencephaly associated with psychomotor retardation and seizures. Features include agyria or pachygyria or laminar heterotopia, severe intellectual disability, motor delay, variable presence of seizures, and abnormalities of corpus callosum, hippocampus, cerebellar vermis and brainstem.