A novel interaction site determines binding between AP180 and AP2 in clathrin mediated endocytosis

The early phases of clathrin mediated endocytosis are organized through a highly complex interaction network mediated by clathrin associated sorting proteins (CLASPs) that comprise long intrinsically disordered regions (IDRs). AP180 is a CLASP exclusively expressed in neurons and comprising a long IDR of around 600 residues, whose function remains partially elusive. Using NMR spectroscopy, we now describe a novel and strong interaction of AP180 with the major adaptor protein AP2 as well as its binding dynamics at atomic resolution. We find that the 70 residue long site determines the overall interaction between AP180 and AP2 in a dynamic equilibrium between its bound and unbound sate, while weaker binding sites contributing to the overall affinity at much high concentrations of AP2. Our data suggest that this novel interaction site might play a central role in recruitment of AP2 to the clathrin coated pit, whereas more transient and promiscuous interactions allow reshaping the interaction network until cargo uptake inside a coated vesicle.