The four inter-ubiquitin ester bonds formed during TLR7 signalling and their location on the surface of ubiquitin.
(A) Schematic showing the time at which each modified ubiquitin was identified after stimulation with R848. All four ester-linked ubiquitylation sites were detected after stimulation for 20 min with R848 (yellow circles) but Thr12 and Thr14 were the only ubiquitylation sites detected after stimulation for 6 h (blue circles). The ubiquitylation of Thr14 was also detected in unstimulated cells. (B) The three-dimensional structure of ubiquitin (PDB: 1UBQ) showing the location of Thr12, Thr14, Ser20 and Thr22 and the seven lysine residues [4].