Positive and negative chemotaxis of enzyme-coated liposome motors.

The ability of cells or cell components to move in response to chemical signals is critical for the survival of living systems. This motion arises from harnessing free energy from enzymatic catalysis. Artificial model protocells derived from phospholipids and other amphiphiles have been made and their enzymatic-driven motion has been observed. However, control of directionality based on chemical cues (chemotaxis) has been difficult to achieve. Here we show both positive or negative chemotaxis of liposomal protocells. The protocells move autonomously by interacting with concentration gradients of either substrates or products in enzyme catalysis, or Hofmeister salts. We hypothesize that the propulsion mechanism is based on the interplay between enzyme-catalysis-induced positive chemotaxis and solute-phospholipid-based negative chemotaxis. Controlling the extent and direction of chemotaxis holds considerable potential for designing cell mimics and delivery vehicles that can reconfigure their motion in response to environmental conditions.