The iodide-transport-defect-causing mutation R124H: A δ-amino group at position 124 is critical for maturation and trafficking of the Na+/I- symporter

Viktoriya Paroder, Juan P. Nicola, Christopher S. Ginter, Nancy Carrasco

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Na+/I- symporter (NIS)-mediated active accumulation of I- in thyrocytes is a key step in the biosynthesis of the iodine-containing thyroid hormones T3 and T4. Several NIS mutants have been identified as a cause of congenital I- transport defect (ITD), and their investigation has yielded valuable mechanistic information on NIS. Here we report novel findings derived from the thorough characterization of the ITD-causing mutation R124H, located in the second intracellular loop (IL-2). R124H NIS is incompletely glycosylated and colocalizes with endoplasmic reticulum (ER)-resident protein markers. As a result, R124H NIS is not targeted to the plasma membrane and therefore does not mediate any I- transport in transfected COS-7 cells. Strikingly, however, the mutant is intrinsically active, as revealed by its ability to mediate I- transport in membrane vesicles. Of all the amino acid substitutions we carried out at position 124 (K, D, E, A, W, N and Q), only Gln restored targeting of NIS to the plasma membrane and NIS activity, suggesting a key structural role for the δ-amino group of R124 in the transporter's maturation and cell surface targeting. Using our NIS homology model based on the structure of the Vibrio parahaemolyticus Na+/galactose symporter, we propose an interaction between the d-amino group of either R or Q124 and the thiol group of C440, located in IL-6. We conclude that the interaction between IL-2 and IL-6 is critical for the local folding required for NIS maturation and plasma membrane trafficking.

Original languageEnglish (US)
Pages (from-to)3305-3313
Number of pages9
JournalJournal of cell science
Issue number15
Publication statusPublished - Sep 9 2013



  • Congenital iodide transport defect
  • Impaired intracellular trafficking
  • Membrane vesicles
  • Na/I symporter (NIS)
  • Plasma membrane targeting

ASJC Scopus subject areas

  • Cell Biology

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