Human SLC26A4/Pendrin STAS domain is a nucleotide-binding protein: Refolding and characterization for structural studies

Mutations in the human SLC26A4/Pendrin polypeptide (hPDS) cause Pendred Syndrome /DFNB4, syndromic deafness with enlargement of the vestibular aqueduct and low-penetrance goiter. Here we present data on cloning, protein overexpression and purification, refolding, and biophysical characterization of the recombinant hPDS STAS domain lacking its intrinsic variable sequence (STAS-ΔIVS). We report a reproducible protein refolding protocol enabling milligram scale expression and purification of uniformly 15N- and 13C/15N-enriched hPDS STAS-ΔIVS domain suitable for structural characterization by solution NMR. Circular dichroism, one-dimensional 1H, two-dimensional 1H-15N HSQC, and 1H-13C HSQC NMR spectra confirmed the well-folded state of purified hPDS STAS-ΔIVS in solution. Heteronuclear NMR chemical shift perturbation of select STAS-ΔIVS residues by GDP was observed at fast-to-intermediate NMR time scales. Intrinsic tryptophan fluorescence quench experiments demonstrated GDP binding to hPDS STAS-ΔIVS with Kd of 178 μM. These results are useful for structure/function characterization of hPDS STAS, the cytoplasmic subdomain of the congenital deafness protein, pendrin, as well as for studies of other mammalian STAS domains.