*4.3. Interface Properties*

For each complex, information on the smallest meaningful biological assembly (chains that can represent the biologically relevant interaction) was taken from DIBS and is indicated in Supplementary Table S1. These contain strictly one IDP chain, which interacts with one or more (but in this case identical) partner chains. An exception is 3O0E, where from the DIBS-indicated L and A chains, L was not present in PDBe PISA, so the equivalent M and B chains have been used. Interface areas, interfacing residues, and interchain physical interactions were derived from PDBe PISA [47] assignments. Total interface areas were defined as the sum of interchain interface areas between the IDP chain and the different interfacing partner chains. The total number of IDP–partner interface H-bonds and salt bridges were also obtained as the sum of such bonds between the IDP chain and the interfacing partner chains, then these were normalized for 1000 Å<sup>2</sup> interface area before statistical comparisons. Interface residues were assigned for each chain based on PISA.
