Determination of the residue-specific 15N CSA tensor principal components using multiple alignment media

Area of Science:

• Biophysics
• Structural Biology
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• The chemical shift anisotropy (CSA) tensor provides insights into local electronic environments and molecular dynamics.
• Understanding the backbone (15)N CSA tensor in proteins is crucial for interpreting NMR data and elucidating protein structure and dynamics.

Purpose of the Study:

• To determine the individual components of the backbone (15)N CSA tensor (sigma(11), sigma(22), sigma(33)) and the orientation of sigma(11) relative to the NH bond (angle beta) for ubiquitin.
• To investigate the correlation between CSA tensor components and protein structural features.

Main Methods:

• Utilized uniformly labeled (15)N, (13)C ubiquitin.
• Employed partial alignment in various media: phospholipid bicelles, Pf1 phage, and poly(ethylene glycol).
• Measured residue-specific residual dipolar couplings and chemical shift deviations.

Main Results:

• Determined individual components of the backbone (15)N CSA tensor and the orientation of sigma(11) relative to the NH bond.
• Found no strong correlation between CSA tensor components and any single structural feature.
• Observed agreement between experimentally determined tensor components and previously reported average CSA principal components.
• Identified significant deviations from average CSA values in beta-strand or extended regions, while alpha-helical residues showed tensor components clustering near the average.

Conclusions:

• The backbone (15)N CSA tensor components are sensitive to local protein secondary structure.
• Deviations in CSA tensor components from average values can serve as indicators of beta-strand and extended conformations.
• Alpha-helical regions exhibit CSA tensor components closer to the average values, suggesting a more uniform local environment.