Characterizing the dimeric protein complexes . Upper panel: the distribution of interface sizes among the 219 complexes. Lower panel: the propensity PX of each amino acid type X to be found in the interface (Eq. 1). Positive (negative) values correspond to types that are overrepresented (underrepresented) in the interfaces, compared to their abundance in the SwissProt data bank. The two shades of grey correspond to the binary amino acid classification.