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Ubiquitin ligases are enzymes involved in the ligation step of ubiquitylation. Ubiquitin ligases bind the substrate protein and catalyse the transfer of ubiquitin from the cysteine of ubiquitin-conjugating enzymes to a lysine residue on the substrate protein.
The HECT-like E3 ligase SopA in Salmonella has been suggested to activate host RING ligases TRIM56 and TRIM65. Here, the authors use mass spectrometry, crystal structures and biochemistry to examine the interactions between these proteins in detail.