Perspective: next generation isotope-aided methods for protein NMR spectroscopy.

Area of Science:

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

Background:

• Conventional NMR methods are limited in obtaining structural information for large proteins and protein complexes.
• Current approaches primarily focus on backbone amide and methyl signals, restricting the scope of investigation.
• The field of integrative structural biology increasingly requires insights into protein dynamics, which are challenging for X-ray crystallography and cryo-electron microscopy.

Purpose of the Study:

• To innovate isotope-aided NMR methodology for investigating large proteins and protein complexes.
• To demonstrate that NMR signals beyond methyl and amide groups can be obtained from large proteins.
• To highlight the potential of these novel NMR probes for studying challenging biological targets and dynamics.

Main Methods:

• Optimization of transverse relaxation properties through advanced isotope labeling, building upon the stereo-array isotope labeling (SAIL) method.
• Development of "TROSY by isotope labeling" techniques to improve signal quality in large molecules.
• Selective deuteration to isolate protons attached to 12C atoms, yielding narrow 1H-NMR signals.

Main Results:

• Successful observation of individual NMR signals for side-chain aliphatic and aromatic 13CH groups in large proteins (e.g., 82 kDa malate synthase G).
• Demonstration that selective deuteration enables narrow 1H-NMR signals from protons attached to 12C in large proteins.
• Direct 1H observation methods show higher sensitivity compared to heteronuclear multidimensional NMR.

Conclusions:

• Novel isotope labeling strategies significantly expand the types of NMR signals accessible for large proteins.
• These advancements open new avenues for studying protein dynamics and challenging targets like membrane proteins and supramolecular complexes.
• Low-dimensional 1H-direct observation NMR methods, revitalized by selective deuteration, are crucial for future ultrahigh-field NMR studies.