Activity and thermal stability of lysozyme in alkylammonium formate ionic liquids—influence of cation modification

Thermal stability of proteins in the presence of aprotic ionic liquids

“…We have found that the activity of protease is highly maintained not only in water-immiscible aprotic ionic liquids but also in water-miscible aprotic ionic liquids as well [22,23]. On the other hand, it has been reported that protic ionic liquids keep the stability of proteins in an aqueous solution at high temperatures [24,25], and amyloid fibrils of proteins are dissolved in protic ionic liquids and are refolded by dilution with an aqueous solution [32]. Moreover, aprotic ionic liquids can refold the denatured protein [33].…”

“…Inorganic salts and glycerol used as a conventional stabilizing agent inhibited the formation of protein aggregation, and exhibited thermal stabilization to some extent. On the other hand, C, protein aggregation is prevented, and any cloudy appearance is absent [25]. The hydrophobic core of lysozyme unfolded by heat interacts with the cation of ionic liquids, and cation adsorption results in acquisition of a net positive charge preventing aggregation via electrostatic repulsion [24].…”

“…In thermal denaturation of lysozyme without protein aggregation, when the hydrophobic core of proteins is exposed, but the disulfide bonds keep intact, denatured proteins spontaneously refold to their native structures on cooling after thermal denaturation [26][27][28][29][30]. The refolding of thermally-denatured proteins is enhanced in the presence of protic ionic liquids such as alkylammonium nitrate and alkylammonium formates [24,25]. Moreover, N'-alkyl and N'-(ω-hydroxyalkyl) N-methylimidazolium chlorides refold denatured proteins such as hen egg white lysozyme and the single-chain antibody fragment ScFvOx [33].…”

“…Moreover, N'-alkyl and N'-(ω-hydroxyalkyl) N-methylimidazolium chlorides refold denatured proteins such as hen egg white lysozyme and the single-chain antibody fragment ScFvOx [33]. activity of lysozyme increases with an increase in the concentration of ethylammonium formate and 2-methoxyethylammonium formate, while the remaining activity increases at low concentration of propylammonium formate, but at higher concentrations of propylammonium formate the protein spontaneously denatures [25]. Thus, the dependence of concentration of ionic liquids on the remaining activity of proteins changes by switching from one ionic liquid to another.…”

“…As a model protein, chicken egg-white lysozyme has been employed, since it is well investigated regarding its structure, properties, functions, and thermostability [16][17][18]24,25 Figure 1. The other reagents were purchased from Sigma-Aldrich Co. (St. Louis, USA).…”