Spin-diffusion couples proton relaxation rates for proteins in exchange with a membrane interface

Area of Science:

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

Background:

• Paramagnetic relaxation agents are crucial for studying molecular dynamics and interactions.
• Nuclear spin-lattice relaxation rates provide insights into molecular motion and environment.
• Proteins interacting with membranes exhibit distinct dynamic behaviors compared to those in solution.

Purpose of the Study:

• To investigate the impact of membrane binding on protein nuclear spin-lattice relaxation rates.
• To compare relaxation dynamics of proteins in solution versus membrane-bound states.
• To understand how molecular environment affects paramagnetic relaxation effects.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was employed to measure spin-lattice relaxation rates.
• Paramagnetic relaxation agents were used to probe protein dynamics.
• Comparative analysis of relaxation rates in solution and membrane-bound protein states.

Main Results:

• Intramolecular cross-relaxation rates were modest for proteins in solution.
• Large differences in oxygen-induced protein-proton relaxation rates were observed in solution.
• Membrane binding dramatically increased intramolecular (1)H cross-relaxation rates due to slow reorientational motion.
• Protein protons exhibited similar spin-lattice relaxation rate constants when membrane-bound, suppressing site-specific effects.

Conclusions:

• Membrane-bound proteins experience significantly altered relaxation dynamics compared to solution states.
• Slow reorientational motion in membrane environments leads to relaxation leveling effects.
• These findings have implications for studying slowly reorienting or rotationally immobilized molecules in vivo using NMR.