Abstract
We introduce a new symmetry-based method for structural investigations of areas surrounding water-exchanging hydrogens in biomolecules by liquid-state nuclear magnetic resonance spectroscopy. Native structures of peptides and proteins can be solved by NMR with fair resolution, with the notable exception of labile hydrogen sites. The reason why biomolecular structures often remain elusive around exchangeable protons is that the dynamics of their exchange with the solvent hampers the observation of their signals. The new spectroscopic method we report allows to locate water-originating hydrogens in peptides and proteins via their effect on nuclear magnetic transitions similar to electronic phosphorescence, long-lived coherences. The sign of long-lived coherences excited in coupled protons can be switched by the experimenter. The different effect of water-exchanging hydrogens on long-lived coherences with opposed signs allows to pinpoint the position of these labile hydrogen atoms in the molecular framework of peptides and proteins.
Highlights
We introduce a new symmetry-based method for structural investigations of areas surrounding waterexchanging hydrogens in biomolecules by liquid-state nuclear magnetic resonance spectroscopy
long-lived coherences (LLC’s) evolve in time, oscillating at a frequency corresponding to the eigenvalue of the eigenstate described in Eq (1) and they decay according to their auto-relaxation rate constants, RLLC and RLLC′: dQLmLoCl,LLC′/dt = − (RLLC,LLC′ + 2πiνLLC)QLmLoCl,LLC′
The diagonalization of the full Liouvillian of a 3-spin system (I,S,K) shows that for small values of J-couplings to the outside spin K with respect to JIS, νLLC ≈ νLLC′ ≈ JIS when JIS is the dominant coupling for the spin system and RLLC is the relaxation rate constant, which effectively describes the decay of www.nature.com/scientificreports the signal
Summary
We introduce a new symmetry-based method for structural investigations of areas surrounding waterexchanging hydrogens in biomolecules by liquid-state nuclear magnetic resonance spectroscopy. These transitions improve spectral resolution, as singlet-triplet long-lived coherences (LLC’s)[21] feature decays up to 9 times slower than those of standard NMR transitions, yielding a proportional narrowing of the observed spectroscopic lines.
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