Figure 6. PDZ protein interaction networks.

(A) Degree analysis of PDZ interactomes shows that all three metazoan networks tested are best approximated by a power-law. (B) Metazoan PDZ encoding genes are largely involved in signaling processes, whereas limited divergence in GO functionality was observed for the PDZ genes of plants and bacteria, for which we mainly categorized protease functions. (C) Comparison of the ligand specific group of PDZ domains (a) to the promiscuous PDZ domain group (b) (described in Fig. 2) shows that both are evenly distributed over the GO components. Numbers refer to: 0: unknown, 1: nucleus specific, 2: cytoplasm specific, 3: plasma membrane specific, 4: mitochondria specific, 5: multiple compartments but non-nuclear, 6: all compartments, 7: extracellular. (D) Distribution by node degree of the two PDZ promiscuity clusters as described in Fig. 4. There was no significant difference found between the two distributions in C (P>0.30) and D (P>0.90), as assessed by student t-test.