Investigating the Activities of Gramicidin a in the Presence of Ionic Liquids(Ils)

Abstract

Ionic liquids(ILs) have been considered as eco-friendly solvent that can replace organic solvent due to their special properties including non-volatility, non-explosiveness, high return yield, and high manipulability. Although ILs are proven as green solvent, the micro-spills into aquatic environment are inevitable. Previous researches have already shown the toxicity of ILs to diverse organisms including bacteria and zebra fish. Our previous research has also shown that the toxicity of ILs to biological organisms may be attributed to the molecular interactions of ILs with cell membranes. However, the effects of ILs on membrane proteins have not been studied yet. The membrane proteins that play important roles in the homeostasis of biological organisms are very susceptible to the perturbation of membranes. It is important to investigate the activities of membrane proteins in the presence of ILs. In this study, we chose gramicidin A(gA) as a model membrane protein. The structure of a membrane is essential to maintain the gA dimers, thus the perturbation of membrane structure may influence the dwell time of gA dimers, resulting in the change of ion current across the membrane; gAs need to be dimerized to permeate ions through the membrane. In order to study the activities of gAs in the presence of ILs, we measured the effects of ILs on gAs using two methods: fluorescence and electrical assay. The effects of ILs increase with regard to the length of alkyl chain and the concentration of ILs. In addition, the flux of monovalent cations is hindered by the positive charge of ionic liquids. Our work suggests that ILs perturb the structure of cell membranes, giving rise to the functional changes of membrane proteins as well. We believe that our research help to design more environment friendly ILs.