Structure and interaction in protein solutions as studied by small-angle neutron scattering

Area of Science:

• Biophysics
• Protein Crystallization
• Solution Chemistry

Background:

• Lysozyme protein crystallization is influenced by solution conditions.
• Understanding salt effects is crucial for protein crystallization.
• The Hoffmeister series describes ion-specific effects in aqueous solutions.

Purpose of the Study:

• To investigate the impact of different potassium halide salts (KF, KCl, KBr) on lysozyme crystallization.
• To elucidate the role of counterion condensation and protein aggregation in salt-induced crystallization.
• To characterize lysozyme's structural and charge properties in solution using SANS.

Main Methods:

• Small-angle neutron scattering (SANS) was employed to study lysozyme solutions.
• Measurements were conducted across varying concentrations of KF, KCl, and KBr.
• Time-resolved SANS experiments were performed before and after crystallization.

Main Results:

• Salt-induced protein crystallization follows the Hoffmeister series (KF < KCl < KBr).
• Lysozyme macromolecules exist as prolate ellipsoids, with effective charge significantly reduced by counterion condensation.
• Salt addition promotes the formation of lysozyme dimers, with aggregation extent correlating with the Hoffmeister series.

Conclusions:

• Counterion condensation and dimer formation are key mechanisms in salt-mediated lysozyme crystallization.
• The observed salt effects align with the established Hoffmeister series.
• SANS provides valuable insights into protein structure, charge, and aggregation dynamics during crystallization.