Puzzle of protein dynamical transition

Area of Science:

• Biophysics
• Materials Science
• Neutron Scattering

Background:

• The dynamics of biological macromolecules are not fully understood, with conflicting models for temperature-dependent mean square displacement (MSD) and relaxation time (τ).
• Previous studies proposed explanations like the fragile-to-strong dynamical crossover (FSC) or instrumental resolution effects for observed transitions.

Purpose of the Study:

• To investigate the nature of the dynamical transition in biological systems, specifically dry and hydrated lysozyme.
• To resolve contradictions in existing models concerning the temperature dependence of macromolecular dynamics.

Main Methods:

• Neutron scattering experiments were conducted on dry and hydrated lysozyme.
• Experiments utilized varying instrumental energy resolutions to probe system dynamics.

Main Results:

• The 'dynamical transition' is an artifact of finite instrumental energy resolution, occurring when system relaxation time matches resolution time.
• No actual transition in dynamical properties of the systems was detected.
• The previously reported change in τ-temperature dependence at 220 K was confirmed and is not an artifact of resolution or numerical errors.

Conclusions:

• The observed dynamical transition in lysozyme is an experimental artifact, not an intrinsic property of the macromolecule.
• The study refutes the fragile-to-strong dynamical crossover as the cause of this artifact.
• The findings clarify the temperature dependence of macromolecular dynamics, resolving long-standing debates.