*2.4. EC Residues Preferentially Occur in Helices in Both IDPs and Partners*

To assess the structural preferences of EC residues, we have computed DSSP secondary structure assignments for the complexes. The EC residues preferentially resided in helices for both IDPs (*p* = 0.003) and partners (*p* = 0.039) compared to other residues (Figure 2D). Also, the detected interprotein ECs typically cluster in one alpha helix of the IDPs, although in most cases the studied chains did not have more: in anti-sigma-28 factor FlgM they cluster in helix4 (Figure 1E), while in RseA in the longer helix of the two (Figure 1F). Furthermore, ECs have also been detected in the toxin-antitoxin MazF-MazE pair, where the IDP MazE does not fold into a regular secondary structure on the surface of the MazF dimer (Figure 1B).
