ci9b01114_si_001.pdf (1.43 MB)
Mapping of Ion and Substrate Binding Sites in Human Sodium Iodide Symporter (hNIS)
journal contribution
posted on 2020-03-11, 19:35 authored by 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 NoskovThe 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.
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Keywords
PET radiotracersLeuT-fold proteinsHuman Sodium Iodide Symporterthyroid hormonessemioccluded statehomology modelinghNIS structurehNIS mutantsimaging ionsbinding sitessubstrate-ion binding pocketsodium iodide symporterHomology modeling3 D models nontrivial3 D organizationcotransported Nadynamics refiningSPECTtheranostic reporter genesequence identityanion transportSubstrate Binding Sitesthyroid glandpermeation pathwaysconsensus model35 hNIS variantsiodide transportercrystal structuresWT hNISmodel predictionsLeuT-fold protein family
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