A Synthetic Gene-Metabolic Oscillator
Fung, E., Wong, W.W., Suen, J.K., Bulter, T., Lee, S.G. and Liao, J.C. (2005) A synthetic gene-metabolic oscillator. Nature, 435, 118-122.
Autonomous oscillations found in gene expression and metabolic, cardiac and neuronal systems have attracted significant attention both because of their obvious biological roles and their intriguing dynamics. In addition, de novo designed oscillators have been demonstrated, using components that arenot part of the natural oscillators. Such oscillators are useful in testing the design principles and in exploring potential applications not limited by natural cellular behaviour transcriptional and metabolic integration characteristic of natural oscillators, here we designed and constructed a synthetic circuit in Escherichia coli K12, using glycolytic flux to generate oscillation through the signalling metabolite acetyl phosphate. If two metabolite pools are interconverted by two enzymes that are placed under the transcriptional control of acetyl phosphate, the system oscillates when the glycolytic rate exceeds a critical value. We used bifurcation analysis to identify the boundaries of oscillation, and verified these experimentally. This work demonstrates the possibility of using metabolic flux as a control factor in system-wide oscillation, as well as the predictability of a de novo gene–metabolic circuit designed using nonlinear dynamic analysis.
Metabolic Engineering and Gene-Metabolic Circuits
Metabolic engineering has achieved encouraging success in producing foreign metabolites in a variety of hosts. However, common strategies for engineering metabolic pathways focus on amplifying the desired enzymes and deregulating cellular controls. As a result, uncontrolled or deregulated metabolic pathways lead to a metabolic imbalance and sub-optimal productivity. We have demonstrated the design and engineering of a regulatory circuit, in addition to amplifying the pathway genes, as the second stage of metabolic engineering effort. In particular, we recruited and altered one of the global regulatory systems in Escherichia coli, the Ntr regulon, to control the engineered lycopene biosynthesis pathway. The altered regulon, stimulated by excess glycolytic flux though sensing of the acetyl phosphate level, controls the expression of two key enzymes in lycopene synthesis in response to flux dynamics. This artificial regulon significantly enhanced lycopene and recombinant protein production and reduced the growth retardation caused by protein overexpression. Projects accomplished are highlighted in the following.