Data collection strategies for time-resolved X-ray free-electron laser diffraction, and 2-color methods

Area of Science:

• Structural Biology
• Biophysics
• X-ray Crystallography

Background:

• Time-resolved X-ray diffraction using X-ray free-electron lasers (XFELs) is crucial for studying dynamic processes in protein nanocrystals.
• Current methods like Monte Carlo pump-probe and fixed sample pump-probe face challenges related to radiation damage and data acquisition efficiency.

Purpose of the Study:

• To compare the error in structure factor measurement for different time-resolved X-ray diffraction schemes.
• To evaluate a proposed two-color method against existing techniques for protein nanocrystal analysis.

Main Methods:

• Monte Carlo pump-probe method with a liquid jet.
• Fixed sample pump-probe (goniometer) method (diffract-and-destroy and below damage dose).
• Proposed two-color method utilizing sequential X-ray pulses of different energies on the same nanocrystal.

Main Results:

• The two-color method eliminates stochastic fluctuations by impressing Bragg spots on the same detector readout.
• For 1% accuracy, the two-color method requires two orders of magnitude fewer diffraction patterns compared to the Monte Carlo liquid jet method.
• Error analysis shows the goniometer method's error is independent of the number of shots, while the two-color and Monte Carlo methods show error inversely proportional to the square root of the number of shots.

Conclusions:

• The proposed two-color method offers a more efficient and accurate approach for time-resolved X-ray diffraction from protein nanocrystals.
• This method mitigates radiation damage and overcomes limitations of existing techniques, particularly regarding sample variability.