Adaptor Related Protein Complex 4 Beta 1 (AP4b1)

The heterotetrameric adaptor protein (AP) complexes sort integral membrane proteins at various stages of the endocytic and secretory pathways.The membrane portion could be partially extracted with high salt, indicating that AP4B1 is a peripheral membrane protein. Gel filtration of human fibroblast cytosol revealed that AP4B1 is part of a 280-kD complex containing other proteins of 140, 50, and 17 kD. Western blot analysis identified these proteins as AP4E1, AP4M1, and AP4S1, respectively. Immunolocalization of AP4B1 in HeLa cells indicated that the AP4 complex associates with the trans-Golgi network or an adjacent structure. This association was sensitive to brefeldin-A treatment, indicating that the membrane localization of AP4 is dependent upon the small GTP-binding protein ARF1.