Structural dynamics in proteins induced by and probed with X-ray free-electron laser pulses

Area of Science:

• Biophysics
• Structural Biology
• Materials Science

Background:

• X-ray free-electron lasers (XFELs) offer advanced crystallographic structure determination.
• Radiation damage limits synchrotron measurements, but XFELs can overcome this.
• Non-uniform ionization in biological samples due to elemental distributions complicates XFEL applications.

Purpose of the Study:

• Investigate femtosecond time-resolved X-ray pump/X-ray probe experiments on protein nanocrystals.
• Understand the impact of dense-environment effects on radiation damage-induced structural dynamics.

Main Methods:

• Femtosecond time-resolved X-ray pump/X-ray probe experiments.
• Analysis of structural changes in protein backbones, aromatic residues, and disulfide bridges.
• Computational simulations to model ion dynamics and screening effects.

Main Results:

• Observed structural changes in protein backbones, aromatic residues, and disulfide bridges.
• Simulations revealed slower-than-expected dynamics of disulfide bridges.
• Identified significant roles of ion caging and plasma electron screening in mitigating damage effects.

Conclusions:

• Dense-environment effects, including ion caging and plasma electron screening, strongly influence local radiation damage dynamics in protein nanocrystals.
• These effects challenge predictions based solely on high atomic charge states.
• Understanding these dynamics is crucial for accurate structural determination using XFELs.