Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 282, Issue 35, Pages 25290-25298Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M700147200
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Funding
- NCI NIH HHS [CA098390] Funding Source: Medline
- NIDDK NIH HHS [DK41544] Funding Source: Medline
- NIGMS NIH HHS [5T32 GM 07491] Funding Source: Medline
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The Na+/I- symporter (NIS) is a key plasma membrane glycoprotein that mediates Na+-dependent active I- transport in the thyroid, lactating breast, and other tissues. The OH group of the side chain at position 354 in transmembrane segment (TMS) IX of NIS has been demonstrated to be essential for NIS function, as revealed by the study of the congenital I- transport defect-causing T354P NIS mutation. TMS IX has the most beta-OH group-containing amino acids (Ser and Thr) of any TMS in NIS. We have thoroughly characterized the functional significance of all Ser and Thr in TMS IX in NIS, as well as of other residues in TMSIX that are highly conserved in other transporters of the SLC5A protein family. Here we show that five beta-OH group-containing residues (Thr-351, Ser-353, Thr-354, Ser-356, and Thr-357) and Asn-360, all of which putatively face the same side of the helix in TMS IX, plus Asp-369, located in the membrane/cytosol interface, play key roles in NIS function and seem to be involved in Na+ binding/translocation.
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