(a) Workflow of RRCS calculation. (b) Examples of RRCS and ΔRRCS calculation for two residues pairs. (c) Statistics of residue contacts and contact types for six receptors (bRho, β2AR, M2R, µOR, A2AR and κ-OR) in their inactive and active states. Contact type describes physicochemical properties of two interacted amino acids that form a pair. The amino acids with hydrophobic side chains (one-letter code: A, V, I, L, M, P, F, Y, W) contribute to the majority of residue contacts, either within themselves (50.1%) or with other amino acids (37.8%).