Functions in an early step of clathrin-mediated endocytosis. Has both a membrane binding/bending activity and the ability to recruit proteins essential to the formation of functional clathrin-coated pits. Has a lipid-binding activity with a preference for membranes enriched in phosphatidylserine and phosphoinositides (Pi(4,5) biphosphate) like the plasma membrane. Its membrane-bending activity might be important for the subsequent action of clathrin and adaptors in the formation of clathrin-coated vesicles. Involved in adaptor protein complex AP-2-dependent endocytosis of the transferrin receptor, it also functions in the AP-2-independent endocytosis of the LDL receptor (By similarity). Homodimer; disulfide-linked. May form homotetramer. Interacts with AP2A1. Interacts with EPS15, EPS15R, ITSN1 and ITSN2; recruit those scaffolding proteins which in turn may interact with the adaptor protein complex AP-2 at the plasma membrane. Interacts with DAB2 (via DPF motifs); mediates LDL receptor/LDLR endocytosis (By similarity). Associated with forming but not mature clathrin-coated vesicles. The recruitment to coated-pits precede the one of clathrin and the adaptor protein complex AP-2 (By similarity). Ubiquitously expressed (at protein level). Ubiquitinated. Mainly undergoes monoubiquitination but also polyubiquitination (By similarity). Belongs to the FCHO family.