Recruitment of Ubiquitin within an E2 Chain Elongation Complex (Biophysical Journal)

The ubiquitin (Ub) proteolysis pathway uses an E1, E2, and E3 enzyme cascade to label substrate proteins with ubiquitin and target them for degradation. The mechanisms of ubiquitin chain formation remain unclear and include a sequential addition model, in which polyubiquitin chains are built unit by unit on the substrate, or a preassembly model, in which polyubiquitin chains are preformed on the E2 or E3 enzyme and then transferred in one step to the substrate. The E2 conjugating enzyme UBE2K has a 150-residue catalytic core domain and a C-terminal ubiquitin-associated (UBA) domain.