Techniques to Study Specific Cell-Surface Receptor-Mediated Cellular Vitamin A Uptake

STRA6 is a multitransmembrane domain protein that was recently identified as the cell-surface receptor for plasma retinol-bindingprotein (RBP), the vitamin A carrier protein in the blood. STRA6 binds to RBP with high affinity and mediates cellular uptakeof vitamin A from RBP. It is not homologous to any known receptors, transporters, and channels, and it represents a new classof membrane transport protein. Consistent with the diverse physiological functions of vitamin A, STRA6 is widely expressedin diverse adult organs and throughout embryonic development. Mutations in human STRA6 that abolish its vitamin A uptake activitycause severe pathological phenotypes in many human organs including the eye, brain, lung, and heart. This chapter describesfunctional assays for STRA6 in live cells and on cellular membranes. These assays can be employed to study the mechanism ofthis new membrane transport mechanism and its roles in the physiology and pathology of many organs.