A photo-responsive transmembrane anion transport relay

Ion transport across lipid membranes in biology is controlled by stimuli-responsive membrane channels and molecular machine ion pumps such as ATPases. Here, we report a synthetic molecular machine-like ion transport relay, in which transporters in opposite sides of a lipid bilayer membrane facilitate transport by passing ions between them. By incorporating a photo-responsive telescopic arm into the relay design, this process is reversibly controlled in response to irradiation with blue and green light. Transport occurs only in the extended state when the length of the arm is sufficient to pass the anion between transporters located on opposite sides of the membrane. In contrast, the contracted state of the telescopic arm is too short to mediate effective transport. The system acts as a stimuli-responsive ensemble of machine-like components, reminiscent of ro-botic arms in a factory assembly line, working cooperatively to mediate ion transport. This work points to new prospects for us-ing lipid bilayer membranes as scaffolds for confining, orientating and controlling the relative positions of molecular machines, thus enabling multiple components to work in concert, and opening up new applications in biological contexts.