Directing Self-Propelled Enzymes and Enzyme-Coated Vesicles Using Chemical Signals

The ability to move both towards and away from specific chemical signals is a critical survival mechanism in living systems. The motion itself arises from the harnessing of free energy from enzymatic catalysis. A variety of enzymes has been shown to undergo positive chemotaxis, moving up their substrate concentration gradient. We propose a general expression for the active movement of an enzyme in a concentration gradient of its substrate. The proposed model takes into account both the substrate-binding and catalytic turnover step, as well as the enhanced diffusion effect of the enzyme. The model is general, has no adjustable parameters, and only requires three experimentally defined constants to quantify chemotaxis. Model enzyme-functionalized synthetic protocells have also been studied and they exhibit both positive and negative chemotaxis based on the interplay between positive enzymatic catalysis-induced chemotaxis and solute-lipid interaction-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.