Rudolf Peierls Centre for Theoretical Physics, University of Oxford , Oxford OX1 3NP , United Kingdom.
Department of Chemistry , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.
Nano Lett. 2018 Apr 11;18(4):2711-2717. doi: 10.1021/acs.nanolett.8b00717. Epub 2018 Mar 22.
Chemotaxis of enzymes in response to gradients in the concentration of their substrate has been widely reported in recent experiments, but a basic understanding of the process is still lacking. Here, we develop a microscopic theory for chemotaxis that is valid for enzymes and other small molecules. Our theory includes both nonspecific interactions between enzyme and substrate as well as complex formation through specific binding between the enzyme and the substrate. We find that two distinct mechanisms contribute to enzyme chemotaxis: a diffusiophoretic mechanism due to the nonspecific interactions and a new type of mechanism due to binding-induced changes in the diffusion coefficient of the enzyme. The latter chemotactic mechanism points toward lower substrate concentration if the substrate enhances enzyme diffusion and toward higher substrate concentration if the substrate inhibits enzyme diffusion. For a typical enzyme, attractive phoresis and binding-induced enhanced diffusion will compete against each other. We find that phoresis dominates above a critical substrate concentration, whereas binding-induced enhanced diffusion dominates for low substrate concentration. Our results resolve an apparent contradiction regarding the direction of urease chemotaxis observed in experiments and, in general, clarify the relation between the enhanced diffusion and the chemotaxis of enzymes. Finally, we show that the competition between the two distinct chemotactic mechanisms may be used to engineer nanomachines that move toward or away from regions with a specific substrate concentration.
酶在其底物浓度梯度下的趋化作用在最近的实验中被广泛报道，但对这一过程的基本理解仍然缺乏。在这里，我们为酶和其他小分子开发了一种微观理论的趋化作用。我们的理论既包括酶和底物之间的非特异性相互作用，也包括酶和底物之间通过特异性结合形成的复合物。我们发现，酶的趋化作用有两种不同的机制：一种是由于非特异性相互作用引起的扩散泳动机制，另一种是由于结合诱导的酶扩散系数变化引起的新机制。如果底物增强了酶的扩散，那么后者的趋化机制会导致酶向较低的底物浓度方向运动；如果底物抑制了酶的扩散，那么后者的趋化机制会导致酶向较高的底物浓度方向运动。对于典型的酶，泳动和结合诱导的增强扩散会相互竞争。我们发现，在临界底物浓度以上泳动占主导地位，而在低底物浓度下，结合诱导的增强扩散占主导地位。我们的结果解决了实验中观察到的脲酶趋化作用方向的明显矛盾，并澄清了增强扩散与酶趋化作用之间的关系。最后，我们表明，两种不同的趋化机制之间的竞争可用于设计向特定底物浓度区域移动或远离该区域的纳米机器。
