Extreme Nonuniform Sampling for Protein NMR Dynamics Studies in Minimal Time

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Protein Dynamics
• Biophysical Chemistry

Background:

• NMR spectroscopy provides quantitative insights into protein dynamics via spin relaxation or chemical exchange saturation transfer (CEST).
• Standard 15N-CEST measurements are time-consuming due to prolonged pseudo-3D HSQC experiments.
• Nonuniform sampling (NUS) can accelerate these experiments but often introduces artifacts, with optimization remaining a challenge.

Purpose of the Study:

• To develop and validate a systematic approach for optimizing NUS schedules for 15N-CEST experiments.
• To significantly reduce measurement times for quantitative multidimensional NMR studies.
• To minimize artifacts associated with accelerated NMR data acquisition.

Main Methods:

• Utilized fitted cross-peaks from reference 2D HSQC experiments as 'footprints' to reconstruct pseudo-3D CEST data.
• Employed linear least-squares fitting to determine cross-peak amplitudes as a function of radiofrequency offset (Δω).
• Implemented spectrum-specific optimized nonuniform sampling (SONUS) schemes based on the Cramer-Rao lower bound metric.

Main Results:

• Achieved a 20-30 fold speed-up in acquiring highly accurate CEST profiles for the protein Im7.
• Demonstrated the effectiveness of using reference experiment cross-peaks for reconstructing undersampled data.
• Identified general properties of optimal sampling schedules through SONUS.

Conclusions:

• The developed method enables dramatic speed-up of quantitative multidimensional NMR measurements.
• This systematic optimization of NUS schedules for 15N-CEST minimizes errors and artifacts.
• The findings pave the way for more efficient studies of protein dynamics in solution.