%0 Journal Article %J Journal of the American Chemical Society %D 2006 %T Diastereomeric Xe chemical shifts in tethered cryptophane cages %A Ruiz, E. J. %A Sears, D. N. %A Pines, A. %A Jameson, C. J. %K chirality %X

Cryptophane cages serve as host molecules to a Xe atom. Functionalization of cryptophane-A has permitted the development of Xe as a biosensor. Synthetic routes used to prepare cryptophanes result in racemic mixtures of the chiral cages. In the preparation of a tethered cryptophane-A cage for biosensor applications, some achiral and chiral substituents such as left-handed amino acids have been used. When the substituent is achiral, the NMR signal of the Xe atom in the functionalized cage in solution is a single isotropic peak, since the Xe shielding tensor components in the R and L cages differ by no more than the signs of the off-diagonal elements. Chiral substituents can split the cage-encapsulated Xe NMR signal into one or more sets of doublets, depending on the number of asymmetric centers in the substituent. We carry out quantum mechanical calculations of Xe nuclear magnetic shielding for the Xe atom at the same strategic position within an L cryptophane-A cage, under the influence of chiral potentials that represent for r or I substituents outside the cage. Calculations of the Xe shielding response in the Lr and LI diastereomeric pairs permit the prediction of the relative order of the Xe chemical shifts in solutions containing the RI and LI diastereomers. Where the substituent itself possesses two chiral centers, comparison of the calculated isotropic shielding responses in the Llr, Lrl, RIl, and Lrr systems, respectively, permits the prediction of the Xe spectrum of diastereomeric systems in solutions containing Llr, RIr, LIl, and RIl systems. Assignment of the peaks observed in the experimental Xe NMR spectra is therefore possible, without having to undertake the difficult synthetic route that produces a single optically pure enantiomer.

%B Journal of the American Chemical Society %V 128 %P 16980-16988 %8 Dec 27 %@ 0002-7863 %G English %U ://WOS:000242941600104 %N 51 %M WOS:000242941600104 %! Diastereomeric Xe chemical shifts in tethered cryptophane cages %R Doi 10.1021/Ja066661z %0 Journal Article %J Protein Science %D 2005 %T Distinguishing multiple chemotaxis Y protein conformations with laser-polarized Xe-129 NMR %A Lowery, T. J. %A Doucleff, M. %A Ruiz, E. J. %A Rubin, S. M. %A Pines, A. %A Wemmer, D. E. %K cavity %X

The chemical shift of the Xe-129 NMR signal has been shown to be extremely sensitive to the local environment around the atom and has been used to follow processes such as ligand binding by bacterial periplasmic binding proteins. Here we show that the Xe-129 shift can sense more subtle changes: magnesium binding, BeF3- activation, and peptide binding by the Escherichia coli chemotaxis Y protein. H-1-N-15 correlation spectroscopy and X-ray crystallography were used to identify two xenon-binding cavities in CheY that are primarily responsible for the shift changes. One site is near the active site, and the other is near the peptide binding site.

%B Protein Science %V 14 %P 848-855 %8 Apr %@ 0961-8368 %G English %U ://WOS:000227738900002 %N 4 %M WOS:000227738900002 %! Distinguishing multiple chemotaxis Y protein conformations with laser-polarized Xe-129 NMR %R Doi 10.1110/Ps.041231005 %0 Journal Article %J Angewandte Chemie-International Edition %D 2004 %T Design of a conformation-sensitive xenon-binding cavity in the ribose-binding protein %A Lowery, T. J. %A Rubin, S. M. %A Ruiz, E. J. %A Pines, A. %A Wemmer, D. E. %K probe %B Angewandte Chemie-International Edition %V 43 %P 6320-6322 %@ 1433-7851 %G English %U ://WOS:000225575600015 %N 46 %M WOS:000225575600015 %! Design of a conformation-sensitive xenon-binding cavity in the ribose-binding protein %R Doi 10.1002/Anie.200460629 %0 Journal Article %J Journal of the American Chemical Society %D 2004 %T Development of a functionalized xenon biosensor %A Spence, M. M. %A Ruiz, E. J. %A Rubin, S. M. %A Lowery, T. J. %A Winssinger, N. %A Schultz, P. G. %A Wemmer, D. E. %A Pines, A. %K drug discovery %X

NMR-based biosensors that utilize laser-polarized xenon offer potential advantages beyond current sensing technologies. These advantages include the capacity to simultaneously detect multiple analytes, the applicability to in vivo spectroscopy and imaging, and the possibility of "remote" amplified detection. Here, we present a detailed NMR characterization of the binding of a biotin-derivatized caged-xenon sensor to avidin. Binding of "functionalized" xenon to avidin leads to a change in the chemical shift of the encapsulated xenon in addition to a broadening of the resonance, both of which serve as NMR markers of ligand-target interaction. A control experiment in which the biotin-binding site of avidin was blocked with native biotin showed no such spectral changes, confirming that only specific binding, rather than nonspecific contact, between avidin and functionalized xenon leads to the effects on the xenon NMR spectrum. The exchange rate of xenon (between solution and cage) and the xenon spin-lattice relaxation rate were not changed significantly upon binding. We describe two methods for enhancing the signal from functionalized xenon by exploiting the laser-polarized xenon magnetization reservoir. We also show that the xenon chemical shifts are distinct for xenon encapsulated in different diastereomeric cage molecules. This demonstrates the potential for tuning the encapsulated xenon chemical shift, which is a key requirement for being able to multiplex the biosensor.

%B Journal of the American Chemical Society %V 126 %P 15287-15294 %8 Nov 24 %@ 0002-7863 %G English %U ://WOS:000225233600051 %N 46 %M WOS:000225233600051 %! Development of a functionalized xenon biosensor %R Doi 10.1021/Ja0483037 %0 Journal Article %J Journal of Molecular Biology %D 2002 %T Detection and characterization of xenon-binding sites in proteins by Xe-129 NMR spectroscopy %A Rubin, S. M. %A Lee, S. Y. %A Ruiz, E. J. %A Pines, A. %A Wemmer, D. E. %K nonpolar cavity %X

Xenon-binding sites in proteins have led to a number of applications of xenon in biochemical and structural studies. Here we further develop the utility of Xe-129 NMR in characterizing specific xenon-protein interactions. The sensitivity of the Xe-129 chemical shift to its local environment and the intense signals attainable by optical pumping make xenon a useful NMR reporter of its own interactions with proteins. A method for detecting specific xenon-binding interactions by analysis of Xe-129 chemical shift data is illustrated using the maltose binding protein (MBP) from Escherichia coli as an example. The crystal structure of MBP in the presence of 8 atm of xenon confirms the binding site determined from NMR data. Changes in the structure of the xenon-binding cavity upon the binding of maltose by the protein can account for the sensitivity of the Xe-129 chemical shift to MBP conformation. Xe-129 NMR data for xenon in solution with a number of cavity containing phage T4 lysozyme mutants show that xenon can report on cavity structure. In particular, a correlation exists between cavity size and the binding-induced Xe-129 chemical shift. Further applications of Xe-129 NMR to biochemical assays, including the screening of proteins for xenon binding for crystallography are considered. (C) 2002 Elsevier Science Ltd. All rights reserved

%B Journal of Molecular Biology %V 322 %P 425-440 %8 Sep 13 %@ 0022-2836 %G English %U ://WOS:000178230500014 %N 2 %M WOS:000178230500014 %! Detection and characterization of xenon-binding sites in proteins by Xe-129 NMR spectroscopy %R Doi 10.1016/S0022-2836(02)00739-8 %0 Journal Article %J Journal of the American Chemical Society %D 2001 %T Detection of a conformational change in maltose binding protein by Xe-129 NMR spectroscopy %A Rubin, S. M. %A Spence, M. M. %A Dimitrov, I. E. %A Ruiz, E. J. %A Pines, A. %A Wemmer, D. E. %K blood %B Journal of the American Chemical Society %V 123 %P 8616-8617 %8 Sep 5 %@ 0002-7863 %G English %U ://WOS:000170729200029 %N 35 %M WOS:000170729200029 %! Detection of a conformational change in maltose binding protein by Xe-129 NMR spectroscopy %R Doi 10.1021/Ja0110325