Figure 1.

The human ufmylation pathway

Pro-UFM1 is cleaved by the UfSPs to expose its C-terminal conserved Gly residue. The mature form of UFM1 is activated by UBA5 at the expense of ATP hydrolysis, forming a high energy thioester bond with Cys 250 of UBA5. The E2 UFC1 then binds to UBA5, and the activated UFM1 is transferred to UFC1, forming a similar thioester linkage with Cys116 in UFC1. Finally, the E3 ligase UFL1 brings in a substrate (Subs) and UFC1-activated UFM1, UFM1 is then conjugated to its substrate. For the reverse process, UfSP2 cleaves UFM1 chains from its substrate. UFM1, ubiquitin-fold modifier 1; Pro-UFM1, UFM1 precursor; UfSP, UFM1-specific protease; UBA5, ubiquitin-like modifier-activating enzyme 5; UFC1, UFM1-conjugating enzyme 1; UFL1, UFM1-specific ligase 1.