AAGAB-orchestrated adaptor complex assembly in snapshots

Yuan Tian, Bing Wang, Rui Yang, Chad A Brautigam, Qian Yin

Florida State University, University of Texas Southwestern Medical Center

Adaptor complexes (APs) are heterotetrameric protein complexes that mediate the intracellular membrane trafficking. The AP complexes bridge vesicular cargo proteins and coat proteins such as the clathrin coat. AP complexes are crucial in regulating cell surface proteome and protein secretion, therefore modulating the cellular responsiveness to internal and external stimuli. While the structures of AP complexes in both cargo-free and cargo-bound forms are well established, we are just starting to unravel the intricacies of AP complex assembly. Alpha and gamma adaptin binding protein (AAGAB) has been identified to govern the early stages of AP complex assembly by stabilizing both the AP2α and AP2σ subunits and forming a stable AAGAB:AP2α:AP2σ hemicomplex. However, the structural basis of molecular recognition between AAGAB and AP subunits is unknown. Here, we report that AAGAB exists as a homodimer, mediated by its C-terminal helical domain (CTD). AAGAB. The crystal structure of AAGAB CTD reveals an antiparallel dimer of bent helices. CTD is both sufficient and essential to recognize and stabilize AP2α subunit, forming binary complexes containing only one copy of AAGAB. Furthermore, AAGAB N-terminal G domain (GD) interacts with AP2σ through a unique interface. Collectively, our findings dissect the functional roles of AAGAB in binding AP subunits, providing a molecular explanation for disease-causing AAGAB mutations.

Dr. Matt Eddy reached out to me for a talk at the biophysics symposium.