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Beschreibung

Tubulin beta chain (UniProt: Q2KJD0, also known as Tubulin beta-5 chain) is encoded by the TUBB gene (Gene ID: 615087) in human. Tubulin is the major constituent of microtubules (MTs). MTs are cytoskeletal filaments composed of?a/beta-tubulin heterodimers that self-assemble head-to-tail to form protofilaments and laterally to form a hollow tube. a/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. Tubulin binds two moles of GTP, one at an exchangeable site on the beta-chain and one at a non-exchangeable site on the a-chain. Tubulin dimers constantly polymerize and depolymerize, and MTs can undergo rapid cycles of assembly and disassembly. The first stage of MT formation, the nucleation phase, is slow. In the presence of Mg2+ and GTP, a and beta tubulins join in an end-to-end manner to form protofilaments with alternating a and beta subunits. GTP bound to beta-tubulin is hydrolyzed to GDP during or immediately after polymerization. This weakens the binding affinity of tubulin for adjacent molecules and favors depolymerization that contributes to the dynamic behavior of MTs. MTs also undergo treadmilling, in which tubulin molecules bound to GDP are continually lost from the minus end and are replaced by the addition of GTP-bound tubulin molecules to the plus end of the same MT. Various post-translational modifications, including acetylation, polyglutamylation, polyglycylation, detyrosination, phosphorylation, and palmitoylation, can regulate the polymerization properties of tubulins and/or their interactions with microtubule associated proteins and motor proteins. beta-Tubulin is reported to undergo phosphorylation on serine 172 by CDK1 during the cell cycle, from metaphase to telophase, but not in interphase. This phosphorylation inhibits tubulin incorporation into microtubules.