No Proton - No problem. Non-protonated Nuclei in NMR Studies of Nucleic Acids
| Authors | |
|---|---|
| Year of publication | 2005 |
| Type | Article in Proceedings |
| Conference | XXI International Conference on MagneticResonance in Biological Systems-Abstracts |
| MU Faculty or unit | |
| Citation | |
| Field | Physical chemistry and theoretical chemistry |
| Keywords | NMR; biological macromolecules; nucleic acids |
| Description | The low proton density in nucleic acids, represents a problem in the structure refinement using NMR data. Six poorly resolved protons found in the RNA ribose moiety, and only one or two non-exchangeable protons in the purine and the pyrimidine bases, produce a limited number of conformationally dependent NOEs. To characterize the structure of a nucleic acid with a good accuracy, it is therefore highly important to supplement the proton NOE data with additional constraints. The proton chemical shifts, as well as the chemical shifts of 13C and 15N nuclei directly attached to protons, are readily available from the assigned 1H - 13C and 1H - 15N one-bond correlation spectra. Also chemical shifts of the glycosidic nitrogens can be obtained from two- or three-dimensional experiments correlating the sugar H1 and base H8/H6 protons. So far, however, little attention has been paid to study the quaternary carbons in nucleic acid bases. Potentially, their chemical shifts, reflecting secondary and tertiary structural arrangements, could be applied as a valuable restraint in the structure refinement. Since the number of quaternary carbons exceeds the number of carbons with directly bonded hydrogens, it is highly desirable to develop a strategy for their detection. New experiments, based both on indirect correlations to remote hydrogens and on direct detection of the 13C nuclei will be presented. In addition, results of ab initio calculations of spin-spin couplings and chemical shielding tensors in purine and pyrimidine bases and their changes upon hydrogen bonding will be dicsussed. |
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