Tubulin is one of several members of a small family of globular proteins. The most common members of the tubulin family are α-tubulin and β-tubulin, the proteins that make up microtubules. Each has a molecular weight of approximately 55 kiloDaltons. Microtubules are assembled from dimers of α- and β-tubulin. These subunits are slightly acidic with an isoelectric point between 5.2 and 5.8. Mutant huntingtin, disrupted intracellular transport and insulin secretion by direct interference with microtubular beta-tubulin. Mutant huntingtin impaired glucose-stimulated insulin secretion in insulin-producing beta cells, without altering stored levels of insulin. Smith et al. (2009) proposed a novel pathogenetic process by which mutant huntingtin may disrupt hormone exocytosis from beta cells and possibly impair vesicular transport in any cell that expresses the pathogenic protein.