I. Rapoport et al., REGULATORY INTERACTIONS IN THE RECOGNITION OF ENDOCYTIC SORTING SIGNALS BY AP-2 COMPLEXES, EMBO journal, 16(9), 1997, pp. 2240-2250
Many plasma membrane proteins destined for endocytosis are concentrate
d into clathrin-coated pits through the recognition of a tyrosine-base
d moth in their cytosolic domains by an adaptor (AP-2) complex. The mu
2 subunit of isolated AP-2 complexes binds specifically, but rather w
eakly, to proteins bearing the tyrosine-based signal. We now demonstra
te, using peptides with a photoreactive probe, that this binding is st
rengthened significantly when the AP-2 complex is present in clathrin
coats, indicating that there is cooperativity between receptor-AP-2 in
teractions and coat formation. Phosphoinositides with a phosphate at t
he D-3 position of the inositol ring, but not other isomers, also incr
ease the affinity of the AP-2 complex for the tyrosine-based moth. AP-
2 is the first protein known (in any context) to interact with phospha
tidyl-inositol 3-phosphate. Our findings indicate that receptor recrui
tment can be coupled to clathrin coat assembly and suggest a mechanism
for regulation of membrane traffic by lipid products of phosphoinosit
ide 3-kinases.