Microfocus diffraction from different regions of a protein crystal: structural variations and unit-cell polymorphism

Area of Science:

• Structural Biology
• Crystallography
• Biophysics

Background:

• Macromolecular crystals are often non-ideal, posing challenges for structure determination.
• These imperfections can also provide insights into crystalline states and macromolecular dynamics.

Purpose of the Study:

• To investigate spatial variations within a single crystal of the dynamic protein EutL.
• To assess if these variations inform about crystal and protein polymorphism.

Main Methods:

• Collected 18 X-ray diffraction datasets from distinct regions of a single EutL crystal using a microfocus synchrotron beam.
• Employed principal component analysis (PCA) to compare structure factors and unit cells across datasets.
• Refined atomic models using merged data from distinct crystal regions.

Main Results:

• PCA separated datasets into two distinct groups with significant unit-cell variations.
• Refined models showed minor but discernible differences in protein structure segments.
• Deviations correlated with regions predicted to have higher dynamic motions via simulations.

Conclusions:

• Individual macromolecular crystals can exhibit significant spatially dependent variations.
• Analyzing multiple datasets from a single crystal can reveal protein dynamics and polymorphism.
• This approach enhances the accuracy of X-ray diffraction experiments.