High-throughput phase-diagram mapping via powder diffraction: a case study of HEWL versus pH

Area of Science:

• Crystallography
• Biochemistry
• Materials Science

Background:

• Hen egg-white lysozyme (HEWL) is a model protein for crystallization studies.
• Understanding protein crystallization is crucial for structural biology and drug development.
• Polycrystalline precipitates of HEWL were formed under controlled conditions.

Purpose of the Study:

• To investigate the structural changes of HEWL precipitates.
• To determine the influence of pH and temperature on HEWL crystal forms.
• To assess the utility of powder X-ray diffraction data for structural analysis.

Main Methods:

• Collection of high-resolution powder X-ray diffraction data.
• LeBail and Pawley/Rietveld refinement analyses.
• Utilized a robotic sample changer for efficient data acquisition.

Main Results:

• Tetragonal and orthorhombic HEWL forms were identified based on crystallization conditions.
• pH-dependent behavior of tetragonal unit-cell parameters was observed.
• Powder diffraction data proved sufficient for molecular replacement and structural refinement.

Conclusions:

• Crystallization conditions significantly impact HEWL crystal structure.
• Powder X-ray diffraction is a viable method for protein structure determination.
• Rietveld analysis yielded a high-quality average structural model of HEWL.