Sorting of integral membrane proteins is mediated vesicular trafficking between a variety of organelles. Two sorting signals are tyrosine-based and dileucine-based signals that interact with heterotetrameric adaptor protein complexes (AP-1, AP-2, AP-3, and AP-4), which are associated with the vesicle coats. These coatomers contain two large adaptin proteins (gamma, alpha, delta, epsilon, and beta1, beta2, beta3, beta4 respectively) that are noncovalently linked to one medium chain (µ1, µ2, µ3, µ4 respectively) and one small chain ( sigma1, sigma2, sigma3, sigma4 respectively). The AP-1 and AP-3 complexes are involved in protein sorting from the TGN and endosomes, while AP-2, µ2 (AP50) interacts with integral membrane proteins via binding to tyrosine-based signals with the canonical motif YXXPhi. In addition, AP50/µ2 is required for both the assembly and the proton transport activity of vacuolar (H+)-ATPases in clathrin coated vesicles. Thus, AP50/µ2 may be involved in targeting integral membrane proteins that are sorted based on tyrosine-based signals and involved in assembly of functional ion channels associated with clathrin coated vesicles.