Interaction Dynamics Determine Signaling and Output Pathway Responses

The understanding of interaction dynamics in signaling pathways can shed light on pathway architecture and provide insights into targets for intervention. Here, we explored the relevance of kinetic rate constants of a key upstream osmosensor in the yeast high-osmolarity glycerol-mitogen-activated protein kinase (HOG-MAPK) pathway to signaling output responses. We created mutant pairs of the Sln1-Ypd1 complex interface that caused major compensating changes in the association (k on ) and dissociation (k off ) rate constants (kinetic perturbations) but only moderate changes in the overall complex affinity (K d ). Yeast cells carrying a Sln1-Ypd1 mutant pair with moderate increases in k on and k off displayed a lower threshold of HOG pathway activation than wild-type cells. Mutants with higher k on and k off rates gave rise to higher basal signaling and gene expression but impaired osmoadaptation. Thus, the k on and k off rates of the components in the Sln1 osmosensor determine proper signaling dynamics and osmoadaptation.