Mapping of Ion and Substrate Binding Sites in Human Sodium Iodide Symporter (hNIS)

Hristina R. Zhekova, Toshie Sakuma, Ryan Johnson, Susanna C. Concilio, Patrycja J. Lech, Igor Zdravkovic, Mirna Damergi, Lukkana Suksanpaisan, Kah Whye Peng, Stephen J. Russell, Sergei Noskov

Research output: Contribution to journalArticlepeer-review

Abstract

The human sodium iodide symporter (hNIS) is a theranostic reporter gene which concentrates several clinically approved SPECT and PET radiotracers and plays an essential role for the synthesis of thyroid hormones as an iodide transporter in the thyroid gland. Development of hNIS mutants which could enhance translocation of the desired imaging ions is currently underway. Unfortunately, it is hindered by lack of understanding of the 3D organization of hNIS and its relation to anion transport. There are no known crystal structures of hNIS in any of its conformational states. Homology modeling can be very effective in such situations; however, the low sequence identity between hNIS and relevant secondary transporters with available experimental structures makes the choice of a template and the generation of 3D models nontrivial. Here, we report a combined application of homology modeling and molecular dynamics refining of the hNIS structure in its semioccluded state. The modeling was based on templates from the LeuT-fold protein family and was done with emphasis on the refinement of the substrate-ion binding pocket. The consensus model developed in this work is compared to available biophysical and biochemical experimental data for a number of different LeuT-fold proteins. Some functionally important residues contributing to the formation of putative binding sites and permeation pathways for the cotransported Na+ ions and I- substrate were identified. The model predictions were experimentally tested by generation of mutant versions of hNIS and measurement of relative (to WT hNIS) 125I- uptake of 35 hNIS variants.

Original languageEnglish (US)
Pages (from-to)1652-1665
Number of pages14
JournalJournal of chemical information and modeling
Volume60
Issue number3
DOIs
StatePublished - Mar 23 2020

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Computer Science Applications
  • Library and Information Sciences

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