Hybrid endosomal coats contain different classes of sorting nexins

Endosomes are protein sorting stations, where multiple membrane coats form tubulovesicular carriers exporting proteins to the Golgi, the plasma membrane, or endo-lysosomal compartments. Distinct classes of sorting nexins are assumed to form distinct homogeneous coats that define the endosomal sorting routes and their cargos. Snx3 and the SNX-BAR proteins Vps5-Vps17 belong to different sorting-nexin classes. They can form homogeneous retromer-dependent coats that differ in structure and in their modes of membrane association and cargo recognition. Here, we describe the formation of hybrid coats between purified SNX-BARs, Snx3, and their cargos. Hybrid coats assemble at variable subunit ratios and diameters and show greater membrane-scaffolding activity than homogeneous coats. In vivo, Snx3 and SNX-BARs co-localise and mutually impact the sorting of their respective cargos. Although simultaneous binding of Snx3- and SNX-BARs to Retromer is sterically prohibited, hybrid coats incorporate both SNXs in a common complex, probably linked by retromer oligomerisation. We hence propose that SNX-BARs and Snx3 form retromer-mediated hybrid coats in novel, stoichiometrically adaptable configurations that allow the adjustment of endosomal carriers for transporting varying ratios of cargo.