Active, Human, Recombinant UBE2S-UBD

Background: The construct joins UBE2S’s UBC core (aa 1-156) to IsoT’s ZnF-UBP (aa 171-250) via a flexible Gly-Ser linker. Crystal and NMR work on the parental domains reveal an open E2 active site aligned coaxially with the ZnF pocket that grips ubiquitin’s Gly-Gly tail, pre-orienting Lys11 for attack. Wild-type UBE2S extends Lys11 chains on APC/C-primed substrates to drive mitotic exit. The fusion mimics this activity without an initiator E2, efficiently decorating Ub-loaded substrates or free ubiquitin to create long Lys11 polymers; in cellular reconstitution, it restores APC/C activity and stimulates substrate priming in trans.