We describe the direct observation of very weak side chain-main chain hydrogen bonding interactions in medium-size 13C/15N-labeled proteins with sensitivity-enhanced NMR spectroscopy. Specifically, the remote correlation between the hydrogen acceptor side chain carboxylate carbon 13CO2(δ) of glutamate 54 and the hydrogen donor backbone amide 15N of methionine 49 in a 12 kDa protein, human FKBP12, is detected via the trans- hydrogen bond (3h)J(NCO2δ) coupling by employing a novel sensitivity- enhanced HNCO-type experiment, CPD-HNCO. The (3h)J(NCO2δ) coupling constant appears to be even smaller than the average value of backbone (3h)J(NC') couplings, consistent with more extensive local dynamics in protein side chains.
- NMR detection
- Sensitivity enhancement
- Side chain-main chain hydrogen bonds
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