Receptor-transporting Protein 1 Short (RTP1S) Mediates Translocation and Activation of Odorant Receptors by Acting through Multiple Steps

Odorant receptor (OR) proteins are retained in the endoplasmic reticulum when heterologously expressed in cultured cells of non-olfactory origins. RTP1S is an accessory protein to mammalian ORs and facilitates their trafficking to the cell-surface membrane and ligand-induced responses in heterologous cells. The mechanism by which RTP1S promotes the functional expression of ORs remains poorly understood. To obtain a better understanding of the role(s) of RTP1S, we performed a series of structure-function analyses of RTP1S in HEK293T cells. By constructing RTP1S deletion and chimera series and subsequently introducing single-site mutations into the protein, we found the N terminus of RTP1S is important for the endoplasmic reticulum exit of ORs and that a middle region of RTP1S is important for OR trafficking from the Golgi to the membrane. Using sucrose gradient centrifugation, we found that the localization of RTP1S to the lipid raft microdomain is critical to the activation of ORs. Finally, in a protein-protein interaction analysis, we determined that the C terminus of RTP1S may be interacting with ORs. These findings provide new insights into the distinct roles of RTP1S in OR translocation and activation.