The Iodide Transport Defect-Causing Y348D Mutation in the Na+/I− Symporter Renders the Protein Intrinsically Inactive and Impairs Its Targeting to the Plasma Membrane

• DOI: 10.1089/thy.2020.0931
• Publication Date: 2021-03-27T10:56:47Z
• Authors: Andrea Reyna-Neyra; Lara Jung; Mayukh Chakrabarti; Mikel X. Suárez; L. Mario Amzel; Nancy Carrasco
• Keywords: Sodium-iodide symporter; Transport protein

Background: The sodium/iodide (Na+/I−) symporter (NIS) mediates active transport of I− into the thyroid gland. Mutations in SLC5A5 gene, which encodes NIS, cause defects (ITDs)—which, if left untreated, lead to congenital hypothyroidism and consequent cognitive developmental deficiencies. ITD-causing NIS mutation Y348D, located transmembrane segment (TMS) 9, was reported three Sudanese patients. Methods: We generated cDNAs coding for Y348D mutants with other hydrophilic hydrophobic amino acid substitutions at position 348 transfected them cells. activity resulting quantitated by radioiodide assays. glycosylation investigated Western blotting after endoglycosidase H (Endo H) PNGase-F glycosidase treatment. Subcellular localization mutant proteins ascertained flow cytometry analysis, cell surface biotinylation, immunofluorescence. intrinsic studied measuring membrane vesicles prepared from Y348D-NIS-expressing Our homology models molecular dynamics simulations were used identify residues that interact Y348 investigate possible interactions between membrane. sequences several Slc5 family transporters aligned, a phylogenetic tree ClustalX. Results: Cells expressing no I−. Furthermore, is only partially glycosylated, retained intracellularly, intrinsically inactive. Hydrophilic than Asp also yield fail be targeted plasma (PM), whereas this position, we show do not membrane, rescue PM targeting function. Conclusions: does reach Hydrophobic 348, however, preserve activity. findings are consistent our model's prediction should face side opposite TMS9 coordinate Na+ participate transport, notion interacts residues. or charged have deleterious effects on activity, residue rescues