Tubulin-folding cofactor B (TBCB) is one of protein cofactors A through E that is required for the folding of tubulins prior to their incorporation into microtubules and heterodimer assembly. TBCB comprises an N-terminal ubiquitin-like (Ubl) domain and a C-terminal cytoskeleton-associated protein with glycine-rich segment (CAP-Gly) domain. The Ubl domain of TBCB is essential for proper folding and assembly of tubulin alpha. It has a β-grasp Ubl fold, a common structure involved in protein-protein interactions. Ubiquitin (Ub) is a protein modifier in eukaryotes that is involved in various cellular processes, including transcriptional regulation, cell cycle control, and DNA repair. TBC-A through E are necessary for the biogenesis of microtubules and for cell viability [, ].
The tubulin heterodimer consists of one alpha- and one beta-tubulin polypeptide. In humans, five tubulin-specific chaperones termed TBCA/B/C/D/E are essential for bring the alpha- and beta-tubulin subunits together into a tightly associated heterodimer. Following the generation of quasi-native beta- and alpha-tubulin polypeptides (via multiple rounds of ATP-dependent interaction with the cytosolic chaperonin), TBCA and TBCB bind to and stabilise newly synthesised beta- and alpha-tubulin, respectively. The exchange of beta-tubulin between TBCA and TBCD, and of alpha-tubulin between TBCB and TBCE, resulting in the formation of TBCD/beta and TBCE/alpha. These two complexes then interact with each other and form a supercomplex (TBCE/alpha/TBCD/beta). Interaction of the supercomplex with TBCC causes the disassembly of the supercomplex and the release of E-site GDP-bound alpha/beta tubulin heterodimer, which becomes polymerization competent following spontaneous exchange with GTP [].This entry represents tubulin binding cofactor A (TBCA) from animal, plants and fungi. Human TBCA functions as a molecular chaperone for beta-tubulin []. Budding yeast TBCA, also known as Rbl2, may bind transiently to free beta-tubulin, which then passes into an aggregated form that is not toxic []. The sequence identity of Rbl2 and human TBCA is only 32%, they appear to be structurally distinct and may interact with beta-tubulin by different mechanisms [].
The tubulin heterodimer consists of one alpha- and one beta-tubulin polypeptide. In humans, five tubulin-specific chaperones termed TBCA/B/C/D/E are essential for bring the alpha- and beta-tubulin subunits together into a tightly associated heterodimer. Following the generation of quasi-native beta- and alpha-tubulin polypeptides (via multiple rounds of ATP-dependent interaction with the cytosolic chaperonin), TBCA and TBCB bind to and stabilise newly synthesised beta- and alpha-tubulin, respectively. The exchange of beta-tubulin between TBCA and TBCD, and of alpha-tubulin between TBCB and TBCE, resulting in the formation of TBCD/beta and TBCE/alpha. These two complexes then interact with each other and form a supercomplex (TBCE/alpha/TBCD/beta). Interaction of the supercomplex with TBCC causes the disassembly of the supercomplex and the release of E-site GDP-bound alpha/beta tubulin heterodimer, which becomes polymerization competent following spontaneous exchange with GTP [].This entry represents tubulin binding cofactor A (TBCA) from animal, plants and fungi. Human TBCA functions as a molecular chaperone for beta-tubulin []. Budding yeast TBCA, also known as Rbl2, may bind transiently to free beta-tubulin, which then passes into an aggregated form that is not toxic []. The sequence identity of Rbl2 and human TBCA is only 32%, they appear to be structurally distinct and may interact with beta-tubulin by different mechanisms []. The structure of TBCA has three helices forming a bundle closed fold with left-handed twist topology going up-and-down.
The tubulin heterodimer consists of one alpha- and one beta-tubulin polypeptide. In humans, five tubulin-specific chaperones termed TBCA/B/C/D/E are essential for bring the alpha- and beta-tubulin subunits together into a tightly associated heterodimer. Following the generation of quasi-native beta- and alpha-tubulin polypeptides (via multiple rounds of ATP-dependent interaction with the cytosolic chaperonin), TBCA and TBCB bind to and stabilise newly synthesised beta- and alpha-tubulin, respectively. The exchange of beta-tubulin between TBCA and TBCD, and of alpha-tubulin between TBCB and TBCE, resulting in the formation of TBCD/beta and TBCE/alpha. These two complexes then interact with each other and form a supercomplex (TBCE/alpha/TBCD/beta). Interaction of the supercomplex with TBCC causes the disassembly of the supercomplex and the release of E-site GDP-bound alpha/beta tubulin heterodimer, which becomes polymerization competent following spontaneous exchange with GTP [].This entry represents tubulin-specific chaperone C (TBCC, also known as tubulin-folding cofactor C), which is involved in the final step of the tubulin folding pathway [, ]. In Arabidopsis thaliana, it is required for continuous microtubule cytoskeleton organisation, mitotic division, cytokinesis, and to couple cell cycle progression to cell division in embryos and endosperms [, ].
The tubulin heterodimer consists of one alpha- and one beta-tubulin polypeptide. In humans, five tubulin-specific chaperones termed TBCA/B/C/D/E are essential for bring the alpha- and beta-tubulin subunits together into a tightly associated heterodimer. Following the generation of quasi-native beta- and alpha-tubulin polypeptides (via multiple rounds of ATP-dependent interaction with the cytosolic chaperonin), TBCA and TBCB bind to and stabilise newly synthesised beta- and alpha-tubulin, respectively. The exchange of beta-tubulin between TBCA and TBCD, and of alpha-tubulin between TBCB and TBCE, resulting in the formation of TBCD/beta and TBCE/alpha. These two complexes then interact with each other and form a supercomplex (TBCE/alpha/TBCD/beta). Interaction of the supercomplex with TBCC causes the disassembly of the supercomplex and the release of E-site GDP-bound alpha/beta tubulin heterodimer, which becomes polymerization competent following spontaneous exchange with GTP [].This entry represents tubulin-folding cofactor D (TBCD) and its homologues. Its ability to interact with beta tubulin is regulated via its interaction with ARL2 (ADP ribosylation factor-like protein 2), a small monomeric G protein. ARL2 inhibits the beta-tubulin GTPase activating protein (GAP) activity of TBCD, and its interaction with native tubulin dimers [, ].
