How Much Entropy Is Contained in NMR Relaxation Parameters?

Area of Science:

• Biophysics
• Structural Biology
• Computational Chemistry

Background:

• Solution-state Nuclear Magnetic Resonance (NMR) relaxation experiments are vital for atomic-level protein dynamics.
• NMR relaxation parameters link protein motions to thermodynamic quantities like conformational entropy.
• Understanding the timescale of entropy accumulation is key to interpreting NMR data.

Purpose of the Study:

• To determine the extent of protein conformational entropy captured by short-time dynamics observable via NMR relaxation.
• To investigate the contribution of slow dynamics (beyond rotational tumbling time) to side-chain conformational entropy.

Main Methods:

• All-atom molecular dynamics (MD) simulations were employed.
• T4 lysozyme was used as a model system.
• Analysis focused on entropy buildup across different timescales.

Main Results:

• Backbone entropy accumulation was found to be rapid, with most entropy captured within the rotational tumbling time (τR).
• Slow dynamics of side chains, occurring on timescales longer than τR, contribute significantly to side-chain conformational entropy.
• A substantial portion of total conformational entropy resides in these slower side-chain motions.

Conclusions:

• Short-time dynamics probed by NMR relaxation capture the majority of backbone entropy.
• Accurate thermodynamic property extraction requires considering the significant contribution of slow side-chain dynamics beyond τR.
• Integrating insights from both fast and slow dynamics is essential for a comprehensive understanding of protein thermodynamics.