Probing ion-binding at a protein interface: Modulation of protein properties by ionic liquids

Area of Science:

• Biochemistry
• Materials Science
• Chemical Engineering

Background:

• Specific ion effects are crucial for modulating protein properties like solubility and stability.
• Ionic liquids (ILs) offer tunable ion combinations with potential for protein property control.
• Understanding protein-IL interactions is essential for leveraging ILs in biotechnology and protein engineering.

Purpose of the Study:

• To investigate the specific ion binding effects of ILs on the model protein lysozyme.
• To determine how ILs influence protein phase behavior, activity, size, conformation, aggregation, and intermolecular interactions.
• To elucidate the mechanisms underlying protein modulation by ILs.

Main Methods:

• Utilized a combination of spectroscopic techniques, activity assays, small-angle X-ray scattering (SAXS), and crystallography.
• Examined lysozyme in dilute and concentrated ionic liquid solutions.
• Compared the effects of different IL anions, specifically formate and nitrate.

Main Results:

• Ionic liquids, particularly their anions, bind to specific sites within the protein hydration layer.
• Specific ion binding can induce conformational flexibility in protein loop regions.
• Nitrate anions promoted higher protein solubility, reduced activity, induced aggregation, and an elongated protein shape compared to formate.
• Protein behavior in ILs is a result of both non-specific interactions and specific ion binding.

Conclusions:

• Protein behavior in ILs is governed by a balance of non-specific interactions and specific ion binding.
• The propensity of IL anions for binding directly correlates with their impact on protein properties.
• Findings provide critical insights into protein-IL interactions and the potential for using ILs to engineer protein characteristics.