InterPro: IPR002453 Beta tubulin

Microtubules are polymers of tubulin, a dimer of two 55kDa subunits, designated alpha and beta [1, 2]. 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 [3]. 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 [4].

Most species, excepting simple eukaryotes, express a variety of closely related alpha- and beta-isotypes. A third family member, gamma tubulin, has also been identified in a number of species [5]. British type familial amyloidosis is an autosomal dominant disease characterised by progressive dementia, spastic paralysis and ataxia. Amyloid deposits from the brain tissue of an individual who died with this disease have been characterised. Trypsin digestion and subsequent N-terminal sequence analysis yielded a number of short sequences, all of which are tryptic fragments of the C-termini of human alpha- and beta-tubulin. Consistent with the definition of amyloid, synthetic peptides based on the sequences of these fragments formed fibrils in vitro, suggesting that the C-termini of both alpha- and beta-tubulin are closely associated with the amyloid deposits of this type of amyloidosis [6]. The amino acid sequences encoded by beta tubulin genes have revealed a high level of overall similarity, but significant divergence between their C-termini [7]. The pattern of expression of the beta-tubulin genes has been studied in several different human cell lines and has revealed varying levels of and differential expression in different cell lines. It appears that distinct human beta-tubulin isotypes are encoded by genes whose exon size and number has been conserved evolutionarily, but whose pattern of expression may be regulated either co-ordinately or uniquely [7].