Gnügge, Robert; Dharmarajan, Lekshmi; Lang, MoritzIST Austria; Stelling, Jörg
Feedback loops in biological networks, among others, enable differentiation and cell cycle progression, and increase robustness in signal transduction. In natural networks, feedback loops are often complex and intertwined, making it challenging to identify which loops are mainly responsible for an observed behavior. However, minimal synthetic replicas could allow for such identification. Here, we engineered a synthetic permease-inducer-repressor system in Saccharomyces cerevisiae to analyze if a transport-mediated positive feedback loop could be a core mechanism for the switch-like behavior in the regulation of metabolic gene networks such as the S. cerevisiae GAL system or the Escherichia coli lac operon. We characterized the synthetic circuit using deterministic and stochastic mathematical models. Similar to its natural counterparts, our synthetic system shows bistable and hysteretic behavior, and the inducer concentration range for bistability as well as the switching rates between the two stable states depend on the repressor concentration. Our results indicate that a generic permease–inducer–repressor circuit with a single feedback loop is sufficient to explain the experimentally observed bistable behavior of the natural systems. We anticipate that the approach of reimplementing natural systems with orthogonal parts to identify crucial network components is applicable to other natural systems such as signaling pathways.
ACS Synthetic Biology
We thank Julio Polaina (Instituto de Agroqu ı ́ mica y Tecnolog ı ́ a de Alimentos, C.S.I.C., Paterna, Spain) for the gift of plasmid pMR4, Gregor W. Schmidt for provision of and support with the micro fl uidic device, Markus Du ̈ rr for the cell tracking R script, and Lukas Widmer for the script for MEIGO using “ parfor ” in MATLAB. We acknowledge the members of the Stelling group for discussions, comments, and support.
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Gnügge R, Dharmarajan L, Lang M, Stelling J. An orthogonal permease–inducer–repressor feedback loop shows bistability. ACS Synthetic Biology. 2016;5(10):1098-1107. doi:10.1021/acssynbio.6b00013
Gnügge, R., Dharmarajan, L., Lang, M., & Stelling, J. (2016). An orthogonal permease–inducer–repressor feedback loop shows bistability. ACS Synthetic Biology, 5(10), 1098–1107. https://doi.org/10.1021/acssynbio.6b00013
Gnügge, Robert, Lekshmi Dharmarajan, Moritz Lang, and Jörg Stelling. “An Orthogonal Permease–Inducer–Repressor Feedback Loop Shows Bistability.” ACS Synthetic Biology 5, no. 10 (2016): 1098–1107. https://doi.org/10.1021/acssynbio.6b00013.
R. Gnügge, L. Dharmarajan, M. Lang, and J. Stelling, “An orthogonal permease–inducer–repressor feedback loop shows bistability,” ACS Synthetic Biology, vol. 5, no. 10, pp. 1098–1107, 2016.
Gnügge R, Dharmarajan L, Lang M, Stelling J. 2016. An orthogonal permease–inducer–repressor feedback loop shows bistability. ACS Synthetic Biology. 5(10), 1098–1107.
Gnügge, Robert, et al. “An Orthogonal Permease–Inducer–Repressor Feedback Loop Shows Bistability.” ACS Synthetic Biology, vol. 5, no. 10, American Chemical Society, 2016, pp. 1098–107, doi:10.1021/acssynbio.6b00013.