*4.4. Amino Acid Compositions*

In the residue and residue group composition analyses, we have calculated the compositions of the trimmed protein segments (analyzed sequence ranges), all interfaces (all IFs), interfaces with no ECs (no-EC IFs), EC-carrying interfaces (EC IFs) and EC residues for the IDPs and partners separately. Identical partner chains have been only included once into these composition analyses. The interfaces have been defined based on PDBe PISA, so regions of the trimmed protein segments falling outside the segments with PDB coordinates are not represented by the interface composition values. However, they are represented in the analyzed sequence ranges and among ECs. Residue groups were defined as: hydrophobic (G, A, V, L, M, I), aromatic (F, Y, W), polar (S, T, C, P, N, Q), negative (D, E), and positive (K, R, H). Residue group and residue proportion significances were obtained by the built-in test of equal proportions of R [62].
