The apical localization of SGLT1 glucose transporter is determined by the short amino acid sequence in its N-terminal domain

SGLT1, an isoform of Na+-dependent glucose cotransporters, is localized at the apical plasma membrane in the epithelial cells of the small intestine and the kidney, where it plays a pivotal role in the absorption and reabsorption of sugars, respectively. To search the domain responsible for the apical localization of SGLT1, we constructed an N-terminal deletion clone series of rat SGLT1 and analyzed the localization of the respective products in Madin-Darby canine kidney (MDCK) cells. The products of N-terminal deletion clones up to the 19th amino acid were localized at the apical plasma membrane, whereas the products of N-terminal 20- and 23-amino-acid deletion clones were localized along the entire plasma membrane. Since single-amino-acid mutations of either D28N or D28G in the N-terminal domain give rise to glucose/galactose malabsorption disease, we examined the localization of these mutants. The products of D28N and D28G clones were localized in the cytoplasm, showing that the aspartic acid-28 may be essential for the delivery of SGLT1 to the plasma membrane. These results suggest that a short amino acid sequence of the N-terminal domain of SGLT1 plays important roles in plasma membrane targeting and specific apical localization of the protein.