- 作者: Chia-Cheng Li; Tin-Yun Ho; Chia-Hung Kao; Shih-Lu Wu; Ji-An Liang; Chien-Yun Hsiang
- 作者服務機構: Graduate Institute of Chinese Medicine, China Medical University, Taichung, Taiwan, R.O.C.
- 中文摘要: --
- 英文摘要:
Background: Sodium/iodide symporter (NIS) mediates the active transport and
accumulation of iodide from the blood into the thyroid gland. His-226 located in the
extracellular region of NIS has been demonstrated to be critical for iodide transport in our
previous study. The conserved charged amino acid residues in the extracellular region of NIS
were therefore characterized in this study.
Methods: Fourteen charged residues (Arg-9, Glu-79, Arg-82, Lys-86, Asp-163, His-226,
Arg-228, Asp-233, Asp-237, Arg-239, Arg-241, Asp-311, Asp-322, and Asp-331) were
replaced by alanine. Iodide uptake abilities of mutants were evaluated by steady-state and
kinetic analysis. The three-dimensional comparative protein structure of NIS was further
modeled using sodium/glucose transporter as the reference protein.
Results: All the NIS mutants were expressed normally in the cells and targeted correctly to
the plasma membrane. However, these mutants, except R9A, displayed severe defects on the
iodide uptake. Further kinetic analysis revealed that mutations at conserved positively
charged amino acid residues in the extracellular region of NIS led to decrease NIS-mediated
iodide uptake activity by reducing the maximal rate of iodide transport, while mutations at
conserved negatively charged residues led to decrease iodide transport by increasing
dissociation between NIS mutants and iodide.
Conclusions: This is the first report characterizing thoroughly the functional significance of
conserved charged amino acid residues in the extracellular region of NIS. Our data suggested
that conserved charged amino acid residues, except Arg-9, in the extracellular region of NIS
were critical for iodide transport. - 中文關鍵字: --
- 英文關鍵字: --