13C-NOESY-HSQC with Split Carbon Evolution for Increased Resolution with Uniformly Labeled Proteins

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Protein Structure Determination
• Biophysical Chemistry

Background:

• Standard 2D 13C-HSQC and 3D 13C-NOESY-HSQC experiments can suffer from signal loss and peak splitting due to long carbon evolution times.
• 13C homonuclear J-couplings often limit spectral resolution and sensitivity in these experiments.
• Improved NMR techniques are crucial for detailed structural analysis of large biomolecules.

Purpose of the Study:

• To introduce and validate two novel pulse sequences for 2D 13C-HSQC and 3D 13C-NOESY-HSQC experiments.
• To enhance spectral resolution in the carbon domain while maintaining good sensitivity, even for large proteins.
• To overcome limitations imposed by 13C homonuclear J-couplings in NMR spectroscopy.

Main Methods:

• Development of pulse sequences with two consecutive carbon evolution periods separated by a z-filter.
• Utilizing a non-constant-time incrementation scheme to minimize J-coupling effects.
• Employing a 13C-13C gradient echo acquisition protocol for data collection.
• Application to uniformly 13C-labeled proteins, including the IIAMan protein from E. coli.

Main Results:

• Achieved nearly twofold enhancement in carbon spectral resolution compared to standard 13C-HSQC at twice the evolution time.
• Demonstrated a 36% decrease in linewidths for the IIAMan protein using the new 13C-HSQC sequence.
• Observed a reduction in signal-to-noise ratio (S/N) of 40% for representative cross-peaks, consistent with increased resolution.
• The derived 13C-NOESY-HSQC experiment provided additional Nuclear Overhauser Effect (NOE) restraints for previously unresolved resonances.

Conclusions:

• The new pulse sequences effectively suppress 13C homonuclear J-couplings, leading to improved spectral resolution and reduced peak splitting.
• These advanced NMR techniques offer enhanced capabilities for structural studies of uniformly 13C-labeled proteins.
• The method provides valuable additional NOE restraints, aiding in the detailed structural elucidation of complex biomolecules.