Abstract
Generation of chemical gradients across biological membranes of cellular compartments is a hallmark of all living systems. Herewe report a proof-of-concept prototype transmembrane pumping systemin 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 (pHin < pHout), 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-based13C 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.
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