Fatty Acid Fueled Transmembrane Chloride Transport

Generation of chemical gradients across biological membranes of cellular compartments is a hallmark of all living systems. Here we report a proof-of-concept prototype transmembrane pumping system in liposomes. The pump uses fatty acid to fuel chloride transport, thus generating a transmembrane chloride gradient. Addition of fatty acid to phospholipid vesicles generates a transmembrane pH gradient (pH_in < pH_out), and this electrochemical H⁺ potential is harnessed by an anionophore to drive chloride efflux via H⁺/Cl^- cotransport. Further addition of fatty acid efficiently fuels the system to continuously drive chloride transport against the concentration gradient, up to [Cl^-]_in 65 mM | [Cl^-]_out 100 mM, and is 1400 times more efficient than using an external fuel. Based on our findings from dissecting the H⁺/Cl^- flux process with the use of different liposomal fluorescence assays, and supported by additional liposome-based ¹³C NMR and DLS studies; we proposed that the presence of an anionophore can induce asymmetric distribution of fatty acid, and contribute to another Cl^- flux mechanism in this system.