[Study of lysozyme by a spin-label method in the 2-mm range]

Area of Science:

• Biophysics
• Chemical Physics
• Spectroscopy

Context:

• Egg lysozyme is a model protein for studying molecular interactions.
• Nitroxyl labels are frequently used spin probes in Electron Spin Resonance (ESR) spectroscopy.
• Understanding protein hydration and dynamics is crucial in biochemistry.

Purpose:

• To investigate the magnetic resonance parameters of egg lysozyme modified with a specific nitroxyl label.
• To elucidate the interactions between the spin label and the lysozyme protein.
• To analyze the temperature-dependent dynamics of the spin label in different sample states.

Summary:

• Electron Spin Resonance (ESR) spectroscopy was employed to study egg lysozyme modified with the nitroxyl label 4-(iodine-acetamide)-2,2,6,6-tetramethylpiperidine-1-oxyl at the hist-15 residue.
• In lyophilic samples, the spin label forms hydrogen bonds with the protein. Upon moistening, it interacts with water molecules.
• Analysis of temperature-dependent ESR line patterns (230-320 K) in moistened samples indicates anisotropic movement of the nitroxyl fragment, with preferential rotation around the N-O bond's Z-axis.

Impact:

• Provides insights into the local environment and dynamics of proteins through spin labeling.
• Demonstrates the utility of ESR spectroscopy in characterizing molecular interactions and hydration effects.
• Contributes to the understanding of protein flexibility and motion at the molecular level.