Chemotaxis: A New Mechanism for Molecular Transport*

In aqueous environments, molecules bounce around through random Brownian walk. However, the environment is often not uniform and there might be a gradient of an interacting solute. In that case, the probe molecules can show directional motion known as chemotaxis. In contrast to diffusion, the chemotactic motion is directional and can be toward or away from high solute concentration which constitutes positive or negative chemotaxis. We have found that enzyme undergoes directional movement towards high concentration of substrate under different conditions, even when the enzyme is not catalyzing the corresponding reaction [1]. In addition to enzymes, we have shown that chemotaxis can happen in a simpler system comprised of dye and interacting polymer molecules [2].
Despite the very different chemistries of the two chemotaxing species (enzyme and dye), the driving force for molecular chemotaxis appears to be similar: the lowering of chemical potential due to a thermodynamically favorable interaction or binding. Based on this thermodynamic insight, we have proposed a general expression to model the observed molecular chemotaxis.

[1] F. Mohajerani, et al. Biochemistry, 2018
[2] R. Guha, et al. J. Am. Chem. Soc., 2017