Can radiation damage to protein crystals be reduced using small-molecule compounds?

Area of Science:

• Crystallography
• Structural Biology
• Radiation Chemistry

Background:

• Protein crystals are susceptible to radiation damage during X-ray diffraction studies.
• A robust metric and data-collection protocol now exist to quantify global radiation damage.
• Small molecules are explored for their potential to mitigate this damage.

Purpose of the Study:

• To evaluate the efficacy of 19 small-molecule compounds in protecting lysozyme crystals from radiation damage.
• To assess the impact of these compounds on crystal lifetime at room temperature and cryogenic conditions.
• To understand the mechanisms underlying compound effectiveness or ineffectiveness in protecting protein crystals.

Main Methods:

• Utilized a defined protocol and metric for measuring global radiation damage.
• Introduced 19 selected small-molecule compounds into lysozyme crystals via cocrystallization or soaking.
• Evaluated compound effects on crystal radiation damage at room temperature and 100 K.

Main Results:

• Twelve compounds showed no protective effect; six compounds exhibited a sensitizing effect.
• Sodium nitrate offered limited protection (factor of two or less) at room temperature in some cases.
• No tested compounds provided protection at 100 K.

Conclusions:

• Scavenger compounds are generally ineffective in protein crystals due to excitation/attack on the protein and low scavenger-to-protein ratios.
• The reactivity of scavengers may lead to sensitization in the protein-dense crystal environment.
• Future efforts should focus on identifying and removing sensitizing compounds from crystallization solutions.