The hormesis characterized by low-concentration stimulation and high-concentration inhibition has gained significant interest over the past decades. Some organic solvents and ionic liquids (ILs) have hormetic concentration responses (HCR) to bioluminescence such as firefly luciferase and Vibrio qinghaiensis sp.-Q67. In this study, we determine the effects of 1-alkyl-3-methylimidazolium chlorine ILs ([Cnmim]Cl, n=2, 4, 6, 8, 10 and 12) to firefly luciferase in order to verify the mechanism of hormesis. The luminescence inhibition toxicity tests show that the stimulation effects of [C8mim]Cl and [C10mim]Cl are obvious, [C6mim]Cl and [C12mim]Cl are minor, and [C2mim]Cl and [C4mim]Cl are rare. The enzyme kinetics show that [C8mim]Cl and [C10mim]Cl are the competitive inhibitors with ATP while [C2mim]Cl and [C4mim]Cl are the noncompetitive ones. Molecular dynamics simulation results reveal that imidazolium rings of [C8mim] and [C10mim] locate at the entrance of luciferin pocket which is adjacent to AMP pocket, while alkyl-chains insert into the bottom of the luciferin pocket. Combining the results from inhibition test, kinetics assay and molecular simulation, we can deduce that occupying AMP pocket by imidazolium ring is responsible for hormetic stimulation.
Keywords: Competitive inhibitor; Hormetic concentration response; Ionic liquid; Luciferase; Molecular dynamics simulation.
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