Determination of peptide backbone torsion angles using double-quantum dipolar recoupling solid-state NMR spectroscopy

Area of Science:

• Biophysical Chemistry
• Structural Biology
• Nuclear Magnetic Resonance Spectroscopy

Background:

• Solid-state NMR (ssNMR) techniques are crucial for high-resolution local structure determination in peptides and proteins.
• Existing dipolar recoupling methods often measure only one torsion angle or are limited to specific secondary structures.
• Suppression of chemical shift anisotropy (CSA) effects at high magnetic fields remains a challenge for many ssNMR techniques.

Purpose of the Study:

• To evaluate the accuracy of Double-Quantum Dipolar Recoupling with a Windowless Sequence (DQ-DRAWS) for measuring Ramachandran torsion angles (phi and psi).
• To demonstrate the method's applicability to diverse secondary structures, irrespective of hydrogen-bonding patterns.
• To showcase the utility of DQ-DRAWS in analyzing heterogeneous protein samples.

Main Methods:

• Utilizing dipolar recoupling ssNMR, specifically the DQ-DRAWS pulse sequence.
• Exciting double-quantum (DQ) coherences between adjacent carbonyl carbons in the peptide backbone.
• Measuring relative orientations of CSA tensors to determine phi and psi torsion angles.

Main Results:

• DQ-DRAWS accurately measures torsion angles for a variety of secondary structures, including helices, beta-sheets, and extended conformations.
• The method is effective regardless of hydrogen-bonding patterns and requires no prior structural information.
• Isotopic labeling and experimental conditions can be optimized for accurate backbone secondary structure measurement.
• DQ-DRAWS demonstrates sensitivity in helix structure determination and distinguishes structures in heterogeneous samples.

Conclusions:

• DQ-DRAWS provides a robust and accurate method for determining local peptide and protein structures using ssNMR.
• The technique overcomes limitations of previous methods by measuring multiple torsion angles and accommodating various secondary structures.
• DQ-DRAWS offers a sensitive and versatile approach for structural analysis, including in complex or heterogeneous systems.