Mapping the endosomal proximity proteome reveals Retromer as a hub for RAB GTPase regulation.
Endosomal retrieval and recycling of integral cargo proteins is essential for cell, tissue and organism-level development and homeostasis and is orchestrated through a specialised retrieval sub-domain on the endosomal vacuole. However, although sub-domain dysfunction is associated with human disease our appreciation of the molecular details and functional components of the retrieval sub-domain(s) remains poorly described. Here, using comparative proximity proteomics of critical retrieval sub-domain components Retromer and Retriever, their cargo adaptors, and a component of the opposing ESCRT-degradative sub-domain, we provide a data-rich resource that identifies new molecular details of retrieval sub-domain composition and organization, including an unrecognised complexity in the interface of Retromer with RAB GTPases. Combining X-ray crystallography and in silico predictions with extensive biochemical and cellular analysis, we dissect the direct association of Retromer with RAB10 regulators DENND4A, DENND4C, TBC1D1, and TBC1D4, and the RAB35 regulator TBC1D13. Overall, we conclude that the Retromer retrieval sub-domain constitutes a major hub for the regulated switching of selected RAB GTPases and propose that this constitutes a major component of the role of Retromer in neuroprotection.