Self-Assembly of DNA and RNA Building Blocks Explored by Nitrogen-14 NMR Crystallography: Structure and Dynamics

Area of Science:

• Biophysical Chemistry
• Structural Biology
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• Nitrogen-15 enrichment of nucleic acids is synthetically challenging and costly.
• Nitrogen-15 NMR studies of nucleic acids lag behind protein studies due to synthetic difficulties and spectral overlap.

Purpose of the Study:

• Develop new NMR methods utilizing the abundant nitrogen-14 isotope for nucleic acid structural characterization.
• Investigate solid-state nitrogen-14 NMR spectra of guanine-based self-assembled quartets.

Main Methods:

• Magic-angle spinning (MAS) NMR spectroscopy.
• 2D double cross-polarization (CP) experiments (1H→14N→1H) to probe proton-nitrogen couplings.
• Density Functional Theory (DFT) calculations for spectral assignment and parameter validation.

Main Results:

• Identified interplane dipolar contacts between stacked guanine quartets.
• Experimental spectra are consistent with in silico internuclear distances.
• Averaging of chemical shifts due to internal motions was interpreted using semiempirical calculations.

Conclusions:

• Solid-state nitrogen-14 NMR is a viable alternative to nitrogen-15 enrichment for studying nucleic acid systems.
• The developed method can be extended to modified nucleobases, nucleosides, and potentially oligonucleotides.
• This approach facilitates structural characterization of DNA and RNA-related systems.