Revealing the complexity of ionic liquid-protein interactions through a multi-technique investigation

Area of Science:

• Biocatalysis
• Protein Stability
• Ionic Liquids

Background:

• Ionic liquids offer tunable properties for biocatalysis.
• Protein and enzyme instability in ionic liquids hinders bioprocessing.
• A comprehensive understanding of ionic liquid-protein interactions is lacking.

Purpose of the Study:

• To develop and apply an analytical framework to study protein interactions with ionic liquids.
• To investigate the structure and stability of green fluorescent protein (GFP) in various ionic liquids.
• To elucidate the mechanisms behind protein destabilization in ionic liquid environments.

Main Methods:

• Utilized a holistic analytical framework combining circular dichroism (CD), fluorescence, UV/Vis spectroscopy, and small-angle X-ray scattering (SAXS).
• Examined the model protein green fluorescent protein (GFP).
• Tested a range of pyrrolidinium and imidazolium salts with different anions (acetate, chloride, triflate).

Main Results:

• Single-technique assessments of protein stability can yield misleading conclusions.
• A holistic framework provides a more accurate understanding of protein stability.
• The triflate anion, despite minimal interaction, induced protein contraction, lowering the unfolding barrier.
• Site-specific ionic liquid-protein interactions were identified.

Conclusions:

• A robust, multi-technique analytical framework is essential for accurately assessing protein stability in ionic liquids.
• Understanding these interactions is critical for advancing non-aqueous biocatalysis.
• Even seemingly benign ionic liquid components can significantly impact protein structure and stability.