Related Experiment Video
Updated: Jul 21, 2026
14:55
Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Dipolar waves as NMR maps of protein structure
Michael F Mesleh1, Gianluigi Veglia, Tara M DeSilva
1Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA.
Journal of the American Chemical Society
|April 19, 2002
Summary
Nuclear magnetic resonance (NMR) spectral analysis reveals unique patterns for mapping protein structure. Dipolar waves and PISEMA wheels offer novel methods for determining molecular topology in aligned protein samples.
Area of Science:
- Structural biology
- Biophysical chemistry
- Nuclear Magnetic Resonance (NMR) spectroscopy
Background:
- Nuclear spin interactions create unique NMR spectral patterns, but angular ambiguities complicate molecular structure determination.
- Periodicity in protein secondary structures can serve as a topological index to overcome these ambiguities.
Purpose of the Study:
- To introduce and validate "dipolar waves" as a method for mapping protein structure using NMR spectra.
- To demonstrate the utility of dipolar waves in both highly and weakly aligned protein samples.
Main Methods:
- Utilizing two-dimensional 1H-15N heteronuclear dipolar/15N chemical shift PISEMA (polarization inversion spin-exchange at the magic angle) spectroscopy for highly aligned helical membrane proteins.
- Extending PISEMA "wheels" to one-dimensional "dipolar waves" for analyzing both highly and weakly aligned samples.
- Analyzing residual dipolar couplings (RDCs) in solution NMR spectra of weakly aligned helices.
Main Results:
- Distinctive "wheel-like" patterns were observed in PISEMA spectra of helical membrane proteins.
- One-dimensional dipolar waves effectively map protein structure in NMR spectra across varying alignment strengths.
- Residual dipolar couplings in weakly aligned samples exhibit properties consistent with dipolar wave analysis.
Conclusions:
- Dipolar waves provide a robust method for protein structure determination by leveraging inherent periodicity.
- This approach bridges solid-state and solution NMR techniques for analyzing weakly aligned protein helices.
- The findings enhance the capability of NMR spectroscopy in elucidating complex protein structures.
Related Concept Videos
03:37Molecular Shape and Polarity
Dipole Moment of a Molecule
02:06Newman Projections
Different notations are used to represent the three-dimensional structure of molecules on two-dimensional surfaces. One of the most commonly used representations is the dash-wedge formula. The dashed wedges, solid wedges, and the plane lines indicate the groups situated behind the plane, coming out of the plane, and in the plane, respectively.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers.
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
01:15¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
01:19NMR Spectroscopy Of Amines
In proton NMR spectroscopy, primary amines and secondary amines showcase their N–H protons as a broad signal in the chemical shift range between δ 0.5 and 5 ppm. The exact position in this range depends on several factors, including sample concentration, hydrogen bonding, and the type of solvent used. Since amine protons undergo fast proton exchange in solution, the protons are labile and therefore do not participate in any splitting with adjacent protons. Thus, the observed peak is broad and...