AAGAB is an assembly chaperone that governs the formation of heterotetrameric adaptor complexes (AP1, AP2, and AP4) involved in clathrin-mediated membrane trafficking 1. Structurally, AAGAB contains an N-terminal pseudoGTPase domain that interacts with σ subunits of AP1 and AP2 complexes through a unique protein-protein interaction interface 2, and a C-terminal domain (CTD) that mediates AAGAB homodimerization and substrate binding 1. AAGAB functions by controlling the ordered sequential assembly of AP2 subunits and stabilizing assembly intermediates; without AAGAB assistance, AP subunits fail to oligomerize and undergo degradation 3. Additionally, AAGAB stabilizes AP-4 ε and σ4 subunits to promote AP-4 complex assembly, which is critical for cargo export from the trans-Golgi network 4. Loss-of-function mutations in AAGAB cause punctate palmoplantar keratoderma type 1A (PPKP1A), a rare skin disease characterized by multiple hyperkeratotic lesions on palms and soles 5. AAGAB variants show clear genotype-phenotype correlation, with all PPKP1A patients presenting the punctate keratoderma subtype 5. Disease-causing mutations typically involve the CTD, compromising protein stability 1. AAGAB represents a model for understanding assembly chaperone mechanisms in membrane trafficking.