Structural mechanisms of cargo adaptors in membrane trafficking

Eukaryotic cells have evolved multiple intracellular trafficking pathways to control the precise sub-cellular localization of proteins and lipids. Key to this process are cargo adaptors, which cooperate with the coat machinery to package and deliver transmembrane cargo with directional specificity. Recent insights indicate how cargo adaptors act as active recognition and regulatory modules to integrate allosteric cues that couple cargo recognition with coat recruitment, coat polymerization, and membrane deformation. In this review, we discuss recent molecular insights into the adaptor protein (AP) family and endosomal sorting nexin (SNX) proteins that recognize cargoes throughout cells. We further highlight how the designation of coat versus adaptor is challenging in systems where these functions have merged into a single complex or cannot be easily ascribed to one versus the other.