Control theoretic properties of physiological controller motifs

Identifying biophysical mechanisms that provide regulation and control is essential for our understanding of living systems. However, the distance between life sciences and control theory can be a challenge. Here, we describe, and show the control theoretic properties of a set of biochemical reaction schemes, so-called controller motifs. These controller motifs have similarities with industrial control systems, and have properties such as setpoints, integral gain, and setpoint weight. Once identified, a system understanding of such mechanisms can help synthetic biologists in selecting suitable targets to alter in construction of new biological systems. From a control theoretic viewpoint we identify which biochemical rate constant or property affect the setpoint and the dynamic response of a biophysical controller motif. We also show how a biological system consisting of two antagonistic regulatory mechanisms can be compared to a control engineering problem of controlling the water level in a tank. The similarity between biological systems and control engineering provides theoretical insight, and clears the way to an engineer's approach to synthetic biology.