Conformation-selective detection of residues in solid proteins under magic-angle-spinning

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
• Protein structure determination
• Biophysical chemistry

Background:

• Distinguishing secondary structures (alpha-helices and beta-sheets) in proteins is crucial for understanding their function.
• Magic-angle-spinning (MAS) NMR is a powerful technique for studying solid proteins.
• Conformation-dependent distances between nuclei can provide structural information.

Purpose of the Study:

• To develop a novel pulse sequence for differentiating protein secondary structures.
• To leverage conformation-dependent nuclear distances for structural analysis.
• To provide a method for simplifying chemical-shift assignments in known protein structures.

Main Methods:

• Utilized a rotational-echo double resonance (REDOR) pulse sequence.
• Exploited differences in distances between amide proton (¹H) and nitrogen (¹⁵N) nuclei.
• Employed a ¹⁵N-REDOR sequence to measure dephasing from remote ¹⁵N nuclei.
• Applied the method to a uniformly ¹³C, ¹⁵N labeled model protein (GB1) under fast magic-angle-spinning (MAS).

Main Results:

• Successfully demonstrated a REDOR-based pulse sequence capable of distinguishing secondary structure elements.
• The method differentiates resonances based on the ψ-torsion angle, correlating with secondary structure.
• Experiments on protein GB1 validated the sequence's effectiveness at a 41.67 kHz MAS frequency.

Conclusions:

• The developed REDOR pulse sequence effectively distinguishes alpha-helical and beta-sheet regions in solid proteins.
• This technique offers a valuable tool for simplifying chemical-shift assignments in proteins with known structures.
• Anticipated direct application in determining protein secondary structures without reliance on ¹³C chemical shifts.