Recombinant TUBE (UBQLN1)

Background: Each UBA (aa 581–624 of UBQLN1) forms a compact three-helix bundle that docks the Ile44 patch of ubiquitin. Four UBAs are arrayed in tandem via Gly/Ser linkers, yielding a 21 kDa monomer that avidly binds polyubiquitin chains but not mono-ubiquitin. TUBEs do not catalyze ubiquitylation; instead, they act as high-affinity scavengers that (i) sequester polyubiquitin chains immediately upon cell lysis, (ii) protect them from DUB cleavage and proteasomal turnover, and (iii) serve as affinity resins for downstream immunoblotting, pulldown-MS or microarray formats. In live-cell imaging, fluorescent TUBEs act as reporters for stress-induced burst ubiquitylation.