Researchers in David Wemmer's group, in collaboration with Alex Pines' group in the Department of Chemistry, have utilized the natural affinity of xenon for hydrophobic protein cavities and the sensitivity of laser-polarized xenon nuclear magnetic resonance to develop a xenon-based method for probing protein conformations in solution. Xenon NMR is able distinguish protein conformations via small hydrophobic cavities that bind xenon in a specific manner.
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Shown
here schematically is a protein (blue) that binds xenon (purple) via a
xenon binding cavity. When the protein binds to its ligand (red) there
is a conformational change that inhibits protein xenon binding. A
corresponding shift in the xenon NMR spectrum is observed.
Currently,
we are using xenon binding cavities that are naturally occurring or
introduced with site-directed mutagenesis to investigate protein
conformational changes induced by ligand binding events,
phosphorylation, and protein-protein association.
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Shown here are laser-polarized xenon NMR spectra of xenon in E. coli cell lysate with and without overexpressed maltose binding protein (MBP). When maltose is added to the lysate, there is a change in the xenon chemical shift only when MBP is present.
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How can xenon detect the MBP ligand binding event in cell lysate? Unlike the other proteins present in E. coli lysate, MBP contains a xenon binding pocket that changes size upon maltose binding, altering its xenon binding properties and therefore the xenon chemical shift.
The availability of numerous NMR spectrometers ranging from 300 to 700 MHz, commercial laser polarizers for xenon optical pumping, the LBL Advanced Light Source sychrotron radiation for x-ray studies, and the expertise in structural biology and NMR have made this interdisciplinary project possible and successful.