Microtubules

Abstract

Microtubules, assembled from heterodimers of α- and β-tubulin, are hollow tubes of about 25 nm in diameter, participating in essential cellular functions such as maintenance of cell shape, cell division, cell motility, and ordered intracellular transport. Tubulin dimers form protofilaments running lengthwise along the microtubule wall with the β-tubulin facing the microtubule plus end conferring a structural polarity. α- and β-Tubulins are highly conserved and consist of isotypes encoded by different genes. Numerous posttranslational modifications of tubulin subunits diversify the surfaces of microtubules and provide a mechanism for their functional specialization. A third member of the tubulin family, γ-tubulin, plays a role in microtubule nucleation. Microtubules display dynamic instability characterized by alternating phases of growth and shrinkage separated by catastrophe and rescue events. The dynamic nature of microtubules is dependent on many microtubule-regulatory proteins.