Promiscuous and multivalent interactions between Eps15 and partner protein Dab2 generate a complex interaction network.

Clathrin-mediated endocytosis depends on complex protein interactions. Eps15 plays a key role through interactions of its three EH domains with Asn-Pro-Phe (NPF) motifs in intrinsically disordered regions (IDRs) of other endocytic proteins. Using nuclear magnetic resonance spectroscopy, we investigate the interaction between Eps15's EH domains and a highly disordered Dab2 fragment (Dab2(320-495)). We find that the EH domains exhibit binding promiscuity, recognizing not only the NPF motif of Dab2 but also other phenylalanine containing motifs. This promiscuity enables interactions with Eps15's own IDR (Eps15(IDR)), which lacks NPF motifs, suggesting a self-inhibitory state that promotes liquid-liquid phase separation. Despite competing for the same EH domain binding sites, Eps15(IDR) and Dab2(320-495) can bind EH123 simultaneously, forming a highly dynamic interaction network that facilitates the recruitment of Dab2(320-495) into Eps15 condensates. Our findings provide molecular insights into the competitive interactions shaping the early stages of clathrin-mediated endocytosis.