Frequencies of the different amino acids in both TM protein interfaces and soluble ones. The TM interfaces are further subdivided into alpha and beta classes. The inset in the top left is a magnification of the lower part of the plot. In the bottom panel we present the same data in terms of distance to the diagonal, including 95% confidence intervals estimated from bootstrapping. The only amino acids for which the confidence intervals are clearly out of the diagonal baseline (representing equal frequencies in soluble and TM) are alanine, glycine and leucine. Note that the scales of top and bottom plots are not the same.