Robust network structure of the Sln1-Ypd1-Ssk1 three-component phospho-relay prevents unintended activation of the HOG MAPK pathway in Saccharomyces cerevisiae

Abstract

BackgroundThe yeast Saccharomyces cerevisiae relies on the high-osmolarity glycerol (HOG) signaling pathway to respond to increases in external osmolarity. The HOG pathway is rapidly activated under conditions of elevated osmolarity and regulates transcriptional and metabolic changes within the cell. Under normal growth conditions, however, a three-component phospho-relay consisting of the histidine kinase Sln1, the transfer protein Ypd1, and the response regulator Ssk1 represses HOG pathway activity by phosphorylation of Ssk1. This inhibition of the HOG pathway is essential for cellular fitness in normal osmolarity. Nevertheless, the extent to and mechanisms by which inhibition is robust to fluctuations in the concentrations of the phospho-relay components has received little attention.ResultsWe established that the Sln1-Ypd1-Ssk1 phospho-relay is robust—it is able to maintain inhibition of the HOG pathway even after significant changes in the levels of its three components. We then developed a biochemically realistic mathematical model of the phospho-relay, which suggested that robustness is due to buffering by a large excess pool of Ypd1. We confirmed experimentally that depletion of the Ypd1 pool results in inappropriate activation of the HOG pathway.ConclusionsWe identified buffering by an intermediate component in excess as a novel mechanism through which a phospho-relay can achieve robustness. This buffering requires multiple components and is therefore unavailable to two-component systems, suggesting one important advantage of multi-component relays.Electronic supplementary materialThe online version of this article (doi:10.1186/s12918-015-0158-y) contains supplementary material, which is available to authorized users.

Interaction Dynamics Determine Signaling and Output Pathway Responses

“…We found that the intermediate Mut 3 is phenotypically similar to WT in almost all aspects tested. This is in agreement with previous computational models of the pathway showing that the phosphorelay of the SLN1 branch is relatively insensitive to small changes in the rate of phosphotransfer or changes in protein abundances (e.g., Krantz et al, 2009;Dexter et al, 2015). However, mutations that lead to a larger increase in both k on and k off (Mut 1 and 2) led to an increase in Hog1-P activation in steady-state environmental conditions indicating that the interaction dynamics are important to set the sensitivity of the osmosensor.…”

Non-invasive and invasive diagnoses of aspergillosis in a rat model by mass spectrometry

“…Upon lung inoculation, the immune system responds to the fungal growth and partially degrades the growing mycelia. Siderophore synthesis and iron uptake are Aspergillus virulence factors that occur at high frequencies 19 . A. fumigatus utilizes the following two systems for iron acquisition: siderophore-mediated iron uptake and reductive iron assimilation 20 .…”

Activation of a Mitogen-Activated Protein Kinase Hog1 by DNA Damaging Agent Methyl Methanesulfonate in Yeast

“…It is possible that MMS treatment could impact the phosphorelay between Ypd1 and Ssk1 by enhancing the interaction between Ypd1 and its interacting partners in the nucleus such as Apn1 or Skn7, thus reducing the availability of cytoplasmic phosphor-Ypd1 to bind and transfer its phosphoryl group to Ssk1. In addition to relaying the phosphoryl group to Ssk1, another established function of Ypd1 is binding to phosphorylated Ssk1 and shielding Ssk1 from the action of phosphatases that dephosphorylate Ssk1 (Saito and Posas, 2012;Dexter et al, 2015). Thus, diminished interaction between Ypd1 and Ssk1 could also contribute to a decrease in the phosphorylation level in Ssk1.…”