The PDB contains many structures containing UBL domains hindering searchability.

We created UbSRD, a structural database of features from UBL-containing structures.

Using UbSRD, we quantified several features of ubiquitin and SUMO recognition.

Ubiquitin rarely has contacts on the backside, the primary binding surface of SUMO.

The ubiquitin tail has many permissible conformations when conjugated to proteins.