Tubulin-folding protein implicated in the first step of the tubulin folding pathway and required for tubulin complex assembly. Involved in the regulation of microtubule polymerization or depolymerization, it modulates microtubule dynamics by capturing GTP-bound beta-tubulin (TUBB). Its ability to interact with beta tubulin is regulated via its interaction with ARL2. Acts as a GTPase-activating protein (GAP) for ARL2. Induces microtubule disruption in absence of ARL2. Increases degradation of beta tubulin, when overexpressed in polarized cells. Promotes epithelial cell detachment, a process antagonized by ARL2. Induces tight adherens and tight junctions disassembly at the lateral cell membrane (PubMed:10722852, PubMed:10831612, PubMed:11847227, PubMed:20740604, PubMed:27666370, PubMed:28158450). Required for correct assembly and maintenance of the mitotic spindle, and proper progression of mitosis (PubMed:27666370). Involved in neuron morphogenesis (PubMed:27666374). Found in a complex with at least ARL2, PPP2CB, PPP2R1A, PPP2R2A, PPP2R5E and TBCD. Interacts with PPP2CB (By similarity). Part of a supercomplex made of cofactors A to E. Cofactors A and D function by capturing and stabilizing tubulin in a quasi-native conformation. Cofactor E binds to the cofactor D-tubulin complex; interaction with cofactor C then causes the release of tubulin polypeptides that are committed to the native state (PubMed:10831612). Interacts with ARL2; interaction is enhanced with the GDP-bound form of ARL2 (PubMed:10831612, PubMed:27666374). Does not interact with ARL3, ARL4A and ARL4D (PubMed:10831612). Interacts with beta tubulin (PubMed:10831612, PubMed:27666370, PubMed:27666374). Interacts with TBCE (PubMed:27666374). Localized in cell-cell contacts. Ubiquitously expressed. Down-regulated by shear stress. The disease is caused by variants affecting the gene represented in this entry. Belongs to the TBCD family. Truncated N-terminus. Extended N-terminus.