Fig. (6) Arrestin molecular mechanism. First, it binds to the cytoplasmic tip of the phosphorilated receptor, occluding the binding site for the heterotrimeric G – protein, preventing its activation (desensitization). Second (not in figure), arrestin links the receptor to elements of the internalization complex, clathrin and its adaptor AP2, which promote receptor mediated endocytosis and subsequent transport to endosomes.