Hybrid endosomal coats containing different classes of sorting nexins

Endosomes are protein sorting stations where multiple 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-BARs Vps5-Vps17 belong to different sorting nexin classes. They form homogeneous Retromer-dependent coats that differ in structure and their modes of membrane association and cargo recognition. Here, we show 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 colocalise 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 to adjust endosomal carriers for transporting varying ratios of cargo.