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 (kon) and dissociation (koff) rate constants (kinetic perturbations) but only moderate changes in the overall complex affinity (Kd). Yeast cells carrying a Sln1-Ypd1 mutant pair with moderate increases in kon and koff displayed a lower threshold of HOG pathway activation than wild-type cells. Mutants with higher kon and koff rates gave rise to higher basal signaling and gene expression but impaired osmoadaptation. Thus, the kon and koff rates of the components in the Sln1 osmosensor determine proper signaling dynamics and osmoadaptation.

The work was supported by European Commission 7th Framework Programme (UNICELLSYS, grant 201142 to L.S., F.P., and E.K.), grants from the Spanish Ministry of Economy and Competitiveness (BFU2012-33503 and FEDER, BFU2014-52125-REDT, BFU14-51672-REDC, and BFU2015-64437-P to F.P.; BFU2014-52333-P to E.d.N.), the Catalan Government (2014 SGR 599), an ERC Advanced Grant 294294 from the EU 7th Framework Programme (SYNCOM, to F.P.), the Fundación Botín, Banco Santander (through its Santander Universities Global Division, to F.P.), and the German Research Council (RTG 1772Computational Systems Biology to E.K.). F.P. and E.d.N. are recipients of an ICREA Acadèmia (Generalitat de Catalunya). This work was supported by the Spanish Ministerio de Economía y Competitividad, Plan Nacional, and the European Fund for Regional Development (BIO2012-39754 to L.S.). We acknowledge support of the Spanish Ministry of Economy and Competitiveness, “Centro de Excelencia Severo Ochoa 2013-2017” (SEV-2012-0208). We acknowledge the support of the CERCA Programme/Generalitat de Catalunya.