Energetic contributions of residues on different faces of interfacial helices. (a) Positioning of side chain residues on a canonical α-helix, (b) percent occurrence of hot spot residues on one, two or three helical faces (total number helices in each category shown in parentheses), (c) percent occurrence of hot spot residues as a function of helix position, (d–f) examples of protein complexes with hot spot residues on one face, two faces and three faces (PDB codes: 1xl3, 1xiu, and 1or7).