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. 2015 Jan 1;27(1-2):65-71.
doi: 10.1080/10610278.2014.906601.

Enantiopure Cryptophane- 129 Xe Nuclear Magnetic Resonance Biosensors Targeting Carbonic Anhydrase

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Free PMC article

Enantiopure Cryptophane- 129 Xe Nuclear Magnetic Resonance Biosensors Targeting Carbonic Anhydrase

Olena Taratula et al. Supramol Chem. .
Free PMC article

Abstract

The (+) and (-) enantiomers for a cryptophane-7-bond-linker-benzenesulfonamide biosensor (C7B) were synthesized and their chirality confirmed by electronic circular dichroism (ECD) spectroscopy. Biosensor binding to carbonic anhydrase II (CAII) was characterized for both enantiomers by hyperpolarized (hp) 129Xe NMR spectroscopy. Our previous study of the racemic (+/-) C7B biosensor-CAII complex [Chambers, et al., J. Am. Chem. Soc. 2009, 131, 563-569], identified two "bound" 129Xe@C7B peaks by hp 129Xe NMR (at 71 and 67 ppm, relative to "free" biosensor at 64 ppm), which led to the initial hypothesis that (+) and (-) enantiomers produce diastereomeric peaks when coordinated to Zn2+ at the chiral CAII active site. Unexpectedly, the single enantiomers complexed with CAII also identified two "bound" 129Xe@C7B peaks: (+) 72, 68 ppm and (-) 68, 67 ppm. These results are consistent with X-ray crystallographic evidence for benzenesulfonamide inhibitors occupying a second site near the CAII surface. As illustrated by our studies of this model protein-ligand interaction, hp 129Xe NMR spectroscopy can be useful for identifying supramolecular assemblies in solution.

Keywords: 129Xe NMR spectroscopy; hyperpolarization; xenon biosensing.

Figures

Figure 1
Figure 1
ECD spectra of enantiopure biosensors (−)-C7B and (+)-C7B in 1,4-dioxane at 298 K. Molar ellipticity (Δε) has units of M−1Lcm−1.
Figure 2
Figure 2
HP 129Xe NMR spectra of (−)-C7B (left column) or (+)-C7B (right column) before and after binding to wild-type carbonic anhydrase II. The first row shows spectra of biosensors (138 μM, (−)-C7B; 147 μM (+)-C7B) dissolved in 90% Tris-SO4 buffer (50 mM, pH 8.0) and 10% glycerol. The second and third rows show spectra for biosensor-CA II binding. Solutions of 1.3 mM CA II in 50 mM Tris-SO4 buffer were titrated with 0.5 and 1.0 equivalents of biosensor, respectively.
Figure 3
Figure 3
HP 129Xe NMR spectra of racemic C7B binding to wild-type carbonic anhydrase II. The C7B biosensor (176 μM) was dissolved in Tris-SO4 buffer (50 mM, pH 8.0) and 10% glycerol. Solution of 1.3 mM CAII in matched Tris-SO4 buffer was titrated to give 1:1 stoichiometry with racemic C7B. The chemical shifts for the two “bound” peaks (72.5, 67.9 ppm) are somewhat shifted from the spectrum in reference [33] due to differences in buffer conditions.
Scheme 1
Scheme 1
Synthesis of enantiopure cryptophane biosensors (−) and (+) C7B from enantiopure tripropargyl cryptophanes (1a, 1b).

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