The yeast histidine protein kinase, Sln1p, mediates phosphotransfer to two response regulators, Ssk1p and Skn7p

Abstract

The Saccharomyces cerevisiae Sln1 protein is a 'twocomponent' regulator involved in osmotolerance. Twocomponent regulators are a family of signal-transduction molecules with histidine kinase activity common in prokaryotes and recently identified in eukaryotes. Phosphorylation of Sln1p inhibits the HOG1 MAP kinase osmosensing pathway via a phosphorelay mechanism including Ypd1p and the response regulator, Ssk1p. SLN1 also activates an MCM1-dependent reporter gene, P-lacZ, but this function is independent of Ssk1p. We present genetic and biochemical evidence that Skn7p is the response regulator for this alternative Sln1p signaling pathway. Thus, the yeast Sln1 phosphorelay is actually more complex than appreciated previously; the Sln1 kinase and Ypd1 phosphorelay intermediate regulate the activity of two distinct response regulators, Ssk1p and Skn7p. The established role of Skn7p in oxidative stress is independent of the conserved receiver domain aspartate, D427. In contrast, we show that Sln1p activation of Skn7p requires phosphorylation of D427. The expression of TRX2, previously shown to exhibit Skn7p-dependent oxidative-stress activation, is also regulated by the SLN1 phosphorelay functions of Skn7p. The identification of genes responsive to both classes of Skn7p function suggests a central role for Skn7p and the SLN1-SKN7 pathway in integrating and coordinating cellular response to various types of environmental stress.

Crystallization and preliminary X-ray analysis of Saccharomyces cerevisiae Ypd1p, a key intermediate in phosphorelay signal transduction

“…The data strongly imply that phosphotransfer from Sln1p to Ypd1p to Skn7p (Asp427) is occurring. Similar results by Li et al (1998) establish that the Sln1p-regulated osmotic stress pathway is bifurcated, with Sln1p kinase transmitting signals via Ypd1p to two response regulators, Ssk1p and Skn7p. Therefore, Ypd1p plays a key role in this increasingly complex signal-transduction pathway in S. cerevisiae.…”

Information processing in the adaptation of Saccharomyces cerevisiae to osmotic stress: an analysis of the phosphorelay system

“…3 This might be due to the fact that the cell needs to circumvent a bottleneck in information shuttling. Ypd1 is able to interact with both Ssk1 in the cytosol as well as nuclear Skn7 (Li et al 1998;Lu et al 2003) to transfer the phosphate to the respective response regulator domain, but a transfer to Ssk1 is strongly favored as demonstrated in Janiak- Spens et al (2005). The phosphoryl group was not observed to be transported back to Ypd1.…”

Mitogen-activated protein kinase signaling pathways of the tangerine pathotype of Alternaria alternata

“…64,66,67 S. cerevisiae has a single HSK, Sln1p, which is required for osmotic adaption via an Ypd1p containing a histidine (His) phosphotransfer (HPt) domain and two response regulators (RR), Ssk1p and Skn7p. [68][69][70] All fungal HSKs identified have both a histidine kinase and a RR domains. 63,65,71 Under normal osmolarity, the Sln1p kinase is spontaneously phosphorylated at a conserved histidine residue.…”

“…In contrast, the phosphorylated Skn7p is active and capable of regulating the genes whose products are responsible for low osmolarity. 68,70 In addition, S. cerevisiae uses a Sho1p protein, independent of HSK, to counteract osmotic stress. 72,73 HSKmediated signals have long been thought to be transduced primarily via the Hog1 MAP kinase pathway.…”

“…68,101 Under oxidative stress, Skn7p is phosphorylated at serine or threonine residue and forms a heterodimer with the stress responsive transcription regulator Yap1. 100,102,103 Interaction between Skn7 and Yap1 regulates numerous genes associated with oxidative stress response.…”