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| Title | Flexible open conformation of the AP-3 complex explains its role in cargo recruitment at the Golgi. |
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| Journal, issue, pages | J Biol Chem, Vol. 297, Issue 5, Page 101334, Year 2021 |
| Publish date | Oct 22, 2021 |
 Authors | Jannis Schoppe / Evelyn Schubert / Amir Apelbaum / Erdal Yavavli / Oliver Birkholz / Heike Stephanowitz / Yaping Han / Angela Perz / Oliver Hofnagel / Fan Liu / Jacob Piehler / Stefan Raunser / Christian Ungermann /  |
| PubMed Abstract | Vesicle formation at endomembranes requires the selective concentration of cargo by coat proteins. Conserved adapter protein complexes at the Golgi (AP-3), the endosome (AP-1), or the plasma membrane ...Vesicle formation at endomembranes requires the selective concentration of cargo by coat proteins. Conserved adapter protein complexes at the Golgi (AP-3), the endosome (AP-1), or the plasma membrane (AP-2) with their conserved core domain and flexible ear domains mediate this function. These complexes also rely on the small GTPase Arf1 and/or specific phosphoinositides for membrane binding. The structural details that influence these processes, however, are still poorly understood. Here we present cryo-EM structures of the full-length stable 300 kDa yeast AP-3 complex. The structures reveal that AP-3 adopts an open conformation in solution, comparable to the membrane-bound conformations of AP-1 or AP-2. This open conformation appears to be far more flexible than AP-1 or AP-2, resulting in compact, intermediate, and stretched subconformations. Mass spectrometrical analysis of the cross-linked AP-3 complex further indicates that the ear domains are flexibly attached to the surface of the complex. Using biochemical reconstitution assays, we also show that efficient AP-3 recruitment to the membrane depends primarily on cargo binding. Once bound to cargo, AP-3 clustered and immobilized cargo molecules, as revealed by single-molecule imaging on polymer-supported membranes. We conclude that its flexible open state may enable AP-3 to bind and collect cargo at the Golgi and could thus allow coordinated vesicle formation at the trans-Golgi upon Arf1 activation. |
 External links | J Biol Chem / PubMed:34688652 / PubMed Central |
| Methods | EM (single particle) |
| Resolution | 9.1 - 10.5 Å |
| Structure data | EMDB-13187, PDB-7p3x: EMDB-13188, PDB-7p3y: EMDB-13189, PDB-7p3z: |
| Source |
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 Keywords |  TRANSPORT PROTEIN / adaptor protein / vesicle transport / AP-3 / homology model |
