Distribution of PPI domain number and PPI domain coverage among human and yeast protein hubs and non-hubs. Proteins in human (A,B) and yeast (C,D) PPI networks are divided into hubs (k ≥ 5) and non-hubs (k < 5). The fraction of hubs and non-hubs with a certain number of PPI domains or PPI domain coverage are plotted against the PPI domain number (A,C) and average PPI domain coverage (B,D).