Impurity effects on lysozyme crystal growth

Area of Science:

• Crystallography
• Materials Science
• Biophysics

Background:

• Crystal quality is crucial for applications like X-ray diffraction.
• Understanding factors affecting crystal growth, such as impurities, is essential.
• Hen egg-white lysozyme serves as a well-established model system for protein crystallization studies.

Purpose of the Study:

• To investigate the relationship between impurity incorporation and crystal quality.
• To analyze the impact of impurities on crystal surface morphology.
• To correlate surface changes with measurable crystal quality parameters.

Main Methods:

• Combined Atomic Force Microscopy (AFM) and X-ray Diffraction (XRD).
• Utilized hen egg-white lysozyme as a model protein.
• Introduced covalently bound lysozyme dimer as a model impurity at varying concentrations (5% and 10%).

Main Results:

• AFM revealed significant surface roughening and step disappearance on the [101] face with increasing impurity concentrations.
• Crystal quality metrics (resolution limit, I/, Rmerge, B-factor) consistently degraded as impurity levels rose.
• A notable drop in the B-factor correlated with observed step roughening at 5% impurity.

Conclusions:

• Impurity incorporation directly influences crystal surface morphology, specifically step growth mechanisms.
• Increased impurity levels lead to a significant decline in overall crystal quality.
• These findings highlight the critical role of controlling impurities for obtaining high-quality protein crystals.