XPORT-Dependent Transport of TRP and Rhodopsin

TRP channels have emerged as key biological sensors in vision, taste, olfaction, hearing, and touch. Despite their importance, virtually nothing is known about the folding and transport of TAP channels during biosynthesis. Here, we identify XPORT (exit protein of rhodopsin and TAP) as a critical chaperone for TAP and its G protein-coupled receptor (GPCR), rhodopsin (Rh1). XPORT is a resident ER and secretory pathway protein that interacts with TAP and Rh1, as well as with Hsp27 and Hsp90. XPORT promotes the targeting of TAP to the membrane in Drosophila S2 cells, a finding that provides a critical first step toward solving a longstanding problem in the successful heterologous expression of TAP. Mutations in xport result in defective transport of TRP and Rh1, leading to retinal degeneration. Our results identify XPORT as a molecular chaperone and provide a mechanistic link between TAP channels and their GPCRs during biosynthesis and transport.