*4.5. Residue–Residue Contact Networks*

Interchain residue–residue atomic contacts have been downloaded from the Protein Contacts Atlas [51] for all the X-ray structures (34/37 complexes) using the default 0.5 Å distance cut-off value in PCA. Only the contact lists between the IDP chain and the relevant partner chains have been used for analysis. The number of atomic contacts between each contacting residue pair has been obtained. Also, the total number of atomic contacts (with all contacting residues) has been calculated for all the residues with at least one such interchain atomic contact. If the same partner residue had atomic contacts with the IDP from more than one partner chain, then those different contact numbers were added up to get the total contact number. Also, for IDP residues, all atomic contacts with partner residues were added up regardless of the partner chain. The calculated totals have been compared between EC and non-EC residues for the IDPs and partners separately.

#### *4.6. Secondary Structure Assignments*

DSSP secondary structure assignments [63] have been obtained for all the residues present in the complex structures in a way that only one of the identical partner chains has been used. The eight DSSP secondary structure element type assignments have been simplified and grouped in the traditional way into three larger classes: helix (G, H, and I), strand (E and B) and loop (S, T, and C). The distribution of residues among different secondary structure element types have been compared between EC residues and non-EC residues for the IDPs and partners separately using the built-in test of equal proportions of R.
