Photoreactive crosslinkers capture the ubiquitin-E2-E3 ligases intermediates.

E3 ligases catalyze the final step in transferring ubiquitin to protein substrates, but resulting intermediates are characterized by conformational flexibility. Recent work by Chandler and colleagues ( Biochem J. (2026) 483, 1115-1130) demonstrates that photocross-linking activity-based probes can trap transient conformations of the intermediates, providing a valuable tool to map interfaces during the ubiquitin transfer process.