Endosomes are major cellular cargo sorting stations routing trans-membrane proteins either for degradation or to retrieval to the Golgi and cell surface. Retrieval defects lead to various pathological conditions, including neurodegenerative disorders such as Alzheimer and Parkinson’s diseases. The Retromer coat is the key molecular machine that functions in the cargo sorting and retrieving from endosomes. Its VPS26/VPS29/VPS35 hetero-trimer associates with various sorting nexins (SNX) including SNX-BARs and SNX3 to generate cargo-loaded tubular carriers that can be transported to destination compartments. Although previously we decipher the ‘canonical’ yeast Retromer:SNX-BAR tubular coat(1), it was unclear how Retromer generates tubules with SNXs that lack BAR domains, and whether the architecture of the metazoan Retromer complex follows same principles.
We used cryo-electron tomography and sub-tomogram averaging approach to capture the structural details of reconstituted Retromer:SNX3-coated tubules of metazoan and fungal origins. Remarkably, these evolutionary distant coats feature essentially identical architecture that provides a mechanistic explanation to Parkinson's disease-linked mutations in humans. We further show that Retromer switches between distinct modes of membrane attachments to function with different adaptors without altering its principal architecture. Our subnanometer-resolved reconstructions also reveal the novel structural basis for the formation of tubular carriers in the absence of canonical membrane-remodelling SNX-BAR adaptors.