Ion Transport

Solving the mystery of iodine uptake

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Science  20 Jun 2014:
Vol. 344, Issue 6190, pp. 1355
DOI: 10.1126/science.344.6190.1355-a

Iodine ion transport by the NIS protein.

PHOTO: ILLUSTRATION: V. ALTOUNIAN/SCIENCE

The thyroid gland produces iodine-containing hormones that regulate metabolism. The cell membrane protein NIS (sodium/iodine symporter) transports iodine into thyroid cells, but because iodine concentrations outside of the cell are so low, how it does so is a mystery. The key? Moving two sodium ions along with the iodine ion, Nicola et al found. NIS also does not bind sodium very tightly, but the high concentrations of sodium outside the cell allow one sodium ion to bind. This binding increases the affinity of NIS for a second sodium ion and also for iodine. With the three ions bound, NIS changes its conformation so that it opens to the inside of the cell, where the sodium concentration is low enough for NIS to release its sodium ions. When the sodium goes away, so does NIS's affinity for iodine, leading NIS to release it.

Nat. Commun. 10.1038/ncomms4948 (2014).

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