Stability and Control of Biomolecular Circuits through Structure

Due to omnipresent uncertainties and environmental disturbances, natural and engineered biological organisms face the challenging control problem of achieving robust performance using unreliable parts. The key to overcoming this challenge rests in identifying structures of biomolecular circuits that are largely invariant despite uncertainties, and building control through such structures. In this work, we show that log derivatives can capture the structural regimes of biocircuits in regulating the production and degradation rates of molecules. We show that log derivatives can establish stability of fixed points based on structure, despite large variations in rates and functional forms of models. Furthermore, we demonstrate how control objectives, such as robust perfect adaptation (i.e. step disturbance rejection), could be implemented through structure. Due to the method's simplicity, structural properties for analysis and design of biomolecular circuits can often be determined by a glance at the equations.