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Residue at position 93 of the Na + /iodide symporter (NIS) plays a critical role in Na + /substrate coupled transport
Author(s) -
Maestas Matthew J.,
Dohán Orsolya,
Paroder Monika,
Nicola Juan Pablo,
Eskandari Sepehr,
Carrasco Nancy
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.936.13
Subject(s) - symporter , chemistry , perchlorate , cotransporter , kinetics , mutant , iodide , biophysics , stereochemistry , transporter , biochemistry , inorganic chemistry , ion , sodium , biology , quantum mechanics , gene , physics , organic chemistry
The Na + /I − symporter (NIS) mediates Na + ‐dependent active I − uptake in the thyroid. We report the electrophysiological characterization of G93R NIS, a clinically‐identified NIS mutation that causes congenital I − transport defect, and other substitutions at position 93. Wild‐type (WT) NIS and G93N, G93T, and G93R mutants were expressed in X. laevis oocytes and the two‐electrode voltage clamp technique was used to study steady‐state and presteady‐state kinetic properties of the transporters. Similar to WT NIS, the G93N and G93T mutants exhibited electrogenic Na + ‐dependent I − transport; however, the mutants displayed reduced apparent affinity for I − (>500 μM vs. 30 μM). In contrast to WT NIS, G93N and G93T NIS mutants exhibited electrogenic transport of perchlorate, an environmental pollutant and well‐known NIS inhibitor. Steady‐state kinetics revealed the apparent affinity of the mutants for perrhenate and perchlorate to be 20–30 μM. Steady‐state Na + kinetics showed a sigmoidal dose‐response relationship with all substrates examined (I − , perchlorate, perrhenate, and chlorate). The Na + apparent affinity (~30 mM) and the Na + Hill coefficient (~2) of the mutants were similar to those of the WT. Presteady‐state currents of the mutants were similar to those of the WT. Although trafficked to the cell surface, G93R NIS was inactive. The data suggest that residue 93 may play a key role in coordinating substrate and/or Na + in the binding pocket. NIH grants S06 GM53933 to S.E. and DK41544 and CA098390 to N.C.