Mechanisms directing stress-specific outputs from a regulatory hub - Hog1 in Candida albicans

Stress-activated protein kinase (SAPK) pathways are important stress signalling modules found in all eukaryotic cells. These pathways comprise of a protein kinase cascade that activates the SAPK by phosphorylation at a conserved TGY motif. However, TGY phosphorylation alone is not sufficient to explain how SAPKs programme stress-specific outputs in response to diverse stress inputs. The Hog1 SAPK is critical for the adaptation of the pathogenic fungus Candida albicans to a diverse range of stresses, and is essential for its virulence. Notably, in addition to TGY phosphorylation, we have found that C. albicans Hog1 is subjected to three further posttranslational modifications in a stress-specific fashion: (a) phosphorylation at T179, (b) oxidation, and (c) S-nitrosylation. Our working hypothesis is that these stress-specific SAPK modifications modulate the stress-specific outputs of Hog1. In this project we will test this, firstly by establishing the impact of blocking these modifications upon the ability of Hog1 to drive stress-specific adaptation in C. albicans. We will then perform complementary interaction, expression and chemogenetic screens to define the Hog1 interactome under different stress conditions. This will allow us to test our prediction that Hog1 phosphorylation, oxidation and S-nitrosylation programme stress-dependent interactions. In addition, the global characterisation of environmentally contingent outputs of the Hog1 interactome will facilitate the identification of those components vital in mediating stress-specific downstream responses. Finally we will establish the impact of the novel posttranslational modifications of Hog1, and the Hog1-dependent stress-specific responses identified in this study, on C. albicans-host interactions and disease progression using well established tools and infection models.