Non-thermal microwave effects on protein dynamics? An X-ray diffraction study on tetragonal lysozyme crystals.

Area of Science:

• Structural biology
• Biophysics
• Crystallography

Background:

• Understanding microwave effects on biological molecules is crucial for applications in medicine and research.
• Protein dynamics and structure are key to biological function.
• Previous studies have suggested potential microwave-induced alterations in biomolecular systems.

Purpose of the Study:

• To investigate the structural and dynamical effects of microwave fields on tetragonal hen egg-white lysozyme single crystals.
• To determine if microwaves cause significant, non-thermal structural changes in proteins.
• To differentiate between thermal and potential non-thermal microwave effects on protein crystals.

Main Methods:

• X-ray diffraction (XRD) was employed to analyze crystal structure and dynamics.
• On-line XRD was performed using a modified slab-line waveguide for controlled microwave exposure.
• Crystals were subjected to varying microwave power levels, and results were compared to temperature-simulated heating.

Main Results:

• High microwave power led to recoverable lattice defects, primarily from water evaporation.
• Lower microwave power induced localized, reproducible changes in atomic mean-square displacements (B factors).
• Some sites showed decreased B factors with increasing microwave power, suggesting localized ordering or reduced motion.

Conclusions:

• Observed effects are largely attributable to thermal heating from unbound water or water evaporation, not resonant microwave absorption by protein vibrations.
• Microwaves appear to have a very small effect on the dynamics and structure of globular proteins at functional hydration levels.
• No evidence of large, microwave-driven displacements of protein structural subunits was found.