| Type: | Family | Name: | Tubulin |
| Description: | Microtubules are polymers of tubulin, a dimer of two 55kDa subunits, designated alpha and beta [, ]. Within the microtubule lattice, alpha-beta heterodimers associate in a head-to-tail fashion, giving rise to microtubule polarity. Fluorescent labelling studies have suggested that tubulin is oriented in microtubules with beta-tubulin toward the plus end [].For maximal rate and extent of polymerisation into microtubules, tubulin requires GTP. Two molecules of GTP are bound at different sites, termed N and E. At the E (Exchangeable) site, GTP is hydrolysed during incorporation into the microtubule. Close to the E site is an invariant region rich in glycine residues, which is found in both chains and is thought to control access of the nucleotide to its binding site [].Most species, excepting simple eukaryotes, express a variety of closely- related alpha- and beta-isotypes. A third family member, gamma tubulin, hasalso been identified in a number of species. Gamma tubulin is found at microtubule-organising centres, such as the spindle poles or the centrosome, suggesting that it is involved in minus-end nucleation of microtubule assembly []. Further eukaryotic tubulins (gamma, epsilon, zeta) that are restricted to certain lineages or species have been reported [].Bacterial and archaeal homologues of tubulin have been discovered. BtubA and BtubB, two bacterial homologues in the genus Prosthecobacter, have probably been derived by horizontal gene transfer [, ]. | Short Name: | Tubulin |
