Figure 1. An example PPI network that includes overlapping and different structural functional groups.

Group G1 is a spoke model in which all spoke proteins interact with the hub protein. Groups G2 and G3 are two cohesive groups that have more interactions within themselves and fewer with the rest of the network. And there are three proteins shared by these two groups. Group G4 is a non-cohesive group of which the members similarly interact with proteins in groups G3 and G5, but not among themselves. Group G5 is another non-cohesive group in which the proteins only have interaction with proteins in group G4, but not among each other.