Chemical exchange spectroscopy based on carbon-13 NMR. Applications to enzymology and protein folding

Abstract We explore how 13 C-based two-dimensional chemical exchange spectroscopy (EXSY) can be used to investigate exchange processes that are slow on the NMR time scale. Results are shown for the mutarotase-catalyzed α →← β isomerization of [1- 13 C]glucose using experiments that detect carbon spins: homonuclear 13 C exchange spectroscopy [ 13 C { 13 C} EXSY] and heteronuclear exchange spectroscopy [ 13 C { 1H} EXSY]; and inverse experiments that select for proton spins attached to 13 C: 1 H− 13 C single-bond correlation exchange spectroscopy [ 1 H { 13 C} SBC-EXSY] and 13 C-filtered 1 H exchange spectroscopy [ 1 H { 1 H }− 13 C ƒ - EXSY ] . The main advantage of 13 C-based exchange experiments is the simplification of complex spectra afforded by incorporation of selective labels. The inherent power of this approach is illustrated with a 1 H { 13 C} SBC-EXSY spectrum showing the native →← denatured interconversion of [ 13 C δ1 ] Trp-staphylococcal nuclease. Certain 13 C-based EXSY experiments are useful for discriminating exchange connectivities from dipole-dipole connectivities.