Ionic liquid induced dehydration and domain closure in lysozyme: FCS and MD simulation

Area of Science:

• Biophysics
• Materials Science
• Protein Dynamics

Background:

• Proteins undergo conformational changes influenced by their environment.
• Room temperature ionic liquids (RTILs) offer unique solvent properties.
• Understanding protein-IL interactions is crucial for biomaterial applications.

Purpose of the Study:

• To investigate the effect of a specific RTIL, [pmim][Br], on the structure and dynamics of the protein lysozyme.
• To elucidate the molecular mechanisms behind RTIL-induced protein conformational changes.

Main Methods:

• Fluorescence Correlation Spectroscopy (FCS) to measure hydrodynamic radius and dynamics.
• Molecular Dynamics (MD) simulations to analyze structural changes and solvation.

Main Results:

• RTIL addition significantly reduced lysozyme's hydrodynamic radius from 18 Å to 11 Å.
• Conformational relaxation time decreased from 65 μs to 5 μs, indicating faster dynamics.
• MD simulations revealed RTIL cation ([pmim](+)) preferential solvation, replacing water and forming a nanoscopic cage around the protein.
• A 'domain closure' was observed, leading to a more compact protein structure.

Conclusions:

• RTILs can induce significant structural compaction and dynamics acceleration in proteins like lysozyme.
• The observed effects are driven by preferential solvation of the protein by RTIL cations.
• This study provides insights into protein behavior in ionic liquid solutions, relevant for bio-nanotechnology.