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Regulatory mechanism for the transmembrane receptor that mediates bidirectional vitamin A transport
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Regulatory mechanism for the transmembrane receptor that mediates bidirectional vitamin A transport
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Regulatory mechanism for the transmembrane receptor that mediates bidirectional vitamin A transport
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Journal Article
Regulatory mechanism for the transmembrane receptor that mediates bidirectional vitamin A transport
2020
Overview
Vitamin A has diverse biological functions and is essential for human survival at every point from embryogenesis to adulthood. Vitamin A and its derivatives have been used to treat human diseases including vision diseases, skin diseases, and cancer. Both insufficient and excessive vitamin A uptake are detrimental, but how its transport is regulated is poorly understood. STRA6 is a multitransmembrane domain cell-surface receptor and mediates vitamin A uptake from plasma retinol binding protein (RBP). STRA6 can mediate both cellular vitamin A influx and efflux, but what regulates these opposing activities is unknown. To answer this question, we purified and identified STRA6-associated proteins in a native mammalian cell type that takes up vitamin A through STRA6 using mass spectrometry. We found that the major protein repeatedly identified as STRA6-associated protein is calmodulin, consistent with the cryogenic electron microscopy (cryo-EM) study of zebrafish STRA6 associated with calmodulin. Using radioactivity-based, high-performance liquid chromatography (HPLC)-based and real-time fluorescence techniques, we found that calmodulin profoundly affects STRA6’s vitamin A transport activity. Increased calcium/calmodulin promotes cellular vitamin A efflux and suppresses vitamin A influx through STRA6. Further mechanistic studies revealed that calmodulin enhances the binding of apo-RBP to STRA6, and this enhancement is much more pronounced for apo-RBP than holo-RBP. This study revealed that calmodulin regulates STRA6’s vitamin A influx or efflux activity by modulating its preferential interaction with apo-RBP or holo-RBP. This molecular mechanism of regulating vitamin A transport may point to new directions to treat human diseases associated with insufficient or excessive vitamin A uptake.
Publisher
National Academy of Sciences
Subject
/ Biological Transport - genetics
/ Cattle
/ Chromatography, High Pressure Liquid
/ Efflux
/ High-performance liquid chromatography
/ Humans
/ Membrane Proteins - genetics
/ Membrane Proteins - metabolism
/ Proteins
/ Receptors, Cell Surface - genetics
/ Regulatory mechanisms (biology)
/ Retinene
/ Retinol-Binding Proteins, Plasma - genetics
