Robustness and fragility in the yeast High Osmolarity Glycerol (HOG) signal transduction pathway

Paper in proceeding, 2009

Cellular signalling networks integrate environmental stimuli with information on cellular status. These networks must be robust against stochastic fluctuations in stimuli as well as in the amounts of signalling components. Here, we challenge the yeast HOG signal transduction pathway with systematic perturbations in components’ expression levels implemented by a “genetic tug-of-war” methodology under various external conditions in search of nodes of fragilities. We observe a substantially higher frequency of fragile nodes in this signal transduction pathway than has been observed for other cellular processes. These fragilities disperse without any clear pattern over biochemical functions or location in pathway topology, with the most sensitive node being the scaffold protein PBS2. They are also largely independent of pathway activation by external stimuli. However, the strongest toxicities are caused by pathway hyperactivation. In silico analysis highlights the impact of model structure on in silico robustness, and suggests complex formation and scaffolding as important contributors to the observed fragility patterns. Thus, in vivo robustness data can be used to discriminate and improve mathematical models.