Protein Conformational Flexibility Enables the Formation of Dense Liquid Clusters: Tests Using Solution Shear

Area of Science:

• Crystallization Science
• Protein Biophysics
• Solution Chemistry

Background:

• Protein crystallization is often preceded by the formation of dense liquid clusters.
• These mesoscopic clusters (around 100 nm) host crystal nucleation and contain a small fraction of the total protein.
• Theories suggest these clusters may comprise partially misfolded protein molecules in single-chain protein solutions.

Purpose of the Study:

• To investigate the role of protein conformation in the formation and stability of dense liquid clusters.
• To test the conjecture that partially misfolded proteins constitute these clusters.
• To understand the influence of mechanical stress on protein cluster dynamics.

Main Methods:

• Perturbation of protein conformation using controlled shear rates on lysozyme solutions.
• Observation and quantification of changes in cluster volume following shear application.
• Analysis of potential conformational changes induced by shear stress.

Main Results:

• Shear rates exceeding a specific threshold, applied for over an hour, significantly reduced the volume of the protein cluster population.
• This reduction indicates a sensitivity of the clusters to mechanical perturbation.
• The observed effect is consistent with shear-induced changes in protein structure.

Conclusions:

• Partial unfolding of lysozyme molecules under shear is a likely mechanism for the observed reduction in cluster volume.
• Shear-induced unfolding exposes hydrophobic surfaces, potentially altering protein-protein interactions within clusters.
• This study provides evidence linking protein conformation and the stability of liquid clusters relevant to nucleation.