Hydrated ionic liquids enhance stability and preserve functionality in transmembrane proteins

Transmembrane proteins, especially α-helical transmembrane proteins, are critical cellular membrane components. They play a crucial role in various biological processes, such as molecular transport, signal transduction, and metabolism. Therefore, structural and functional studies are essential for the advancement of fields such as fundamental biology, medical science, drug discovery, biotechnology, and bioengineering. However, challenges such as insolubility and the preservation of native structure have hindered research progress. Various methods, including amphiphilic molecule development and the use of nanodiscs, have been adopted to address these challenges. However, a simple and effective method for the stable handling of membrane proteins is yet to be developed. This study introduces hydrated ionic liquids that directly and stably dissolve transmembrane proteins, including TehA and bacteriorhodopsin. Careful selection of the basic backbone and functional groups of the component cations, along with the kosmotropicity of the anions, revealed that these proteins can be dissolved while retaining their higher-order structure and functionality. The thermodynamic stability of these transmembrane proteins increased by over 20 °C. Bacteriorhodopsin, a light-driven H⁺ transporter, retained its functional capacity. Additionally, its resistance to laser irradiation significantly improved. This study highlights the crucial role of hydration state and specific ionic interactions in the preservation of transmembrane protein structure and functionality. This enhanced stability facilitates the physicochemical analyses of transmembrane protein structures and functions. Furthermore, it opens new avenues for drug discovery and transmembrane protein-based device development through more efficient screening techniques.