Residue propensity (inPro) indicates the relative frequency of different amino acid (AA) residues in dom-faces of complexes. We estimated residue propensities for all dom-faces using Equation 3 [16], where AAPi in Supplementary Table One [see Additional file 1] is the natural logarithm of each AA propensity and NR is the total number of residues in a dom-face. AA propensities for 20 amino acids over our data sets of 354 dom-faces were calculated using Supplementary Equation One [see Additional file 1].