Each subunit has a specific function. Adaptins recognise and bind to clathrin through their hinge region (clathrin box), and recruit accessory proteins that modulate AP function through their C-terminal ear (appendage) domains. Mu recognises tyrosine-based sorting signals within the cytoplasmic domains of transmembrane cargo proteins. One function of clathrin and AP2 complex-mediated endocytosis is to regulate the number of GABA(A) receptors available at the cell surface .