| dc.description.abstract | Phosphoinositides (PIPs) are phosphorylated derivatives of a membrane lipid called phosphatidylinositol that act as signaling molecules. These signaling molecules regulate hundreds of biological events ranging from growth, proliferation, migration, autophagy, exo- and endocytosis. Consequently, when these signaling pathways become dysfunctional, they lead to a wide array of devastating diseases such as diabetes, Alzheimer’s disease, cancer, and developmental disorders. However, there are only a handful of distinct PIP species in eukaryotes; only five in yeast and seven in mammals. Therefore, an unresolved question in the field of PIP signaling is: how can such a limited number of PIP species properly regulate such a wide array of complex and essential biological functions?
In this context, Sec14-like phosphatidylinositol transfer proteins (PITPs) channel phosphatidylinositol 4-OH kinase activities to specific yet diverse biological outcomes. PITPs are predicted to sense and translate specific lipid metabolic information into phosphoinositide signaling events that initiate distinct biological functions through a biophysical mechanism called heterotypic ligand exchange. The characterization of individual members of the yeast Sec14 PITP family will reveal more about the individual biological functions they regulate; especially in terms of the lipid composition the functions require.
The overarching aim of this research was to elucidate the functional and biophysical characteristics of the yeast Sec14-like PITP, Sfh2. This aim was attained by determining the biological function of Sfh2, identifying its secondary ligand, and characterizing its ligand-binding dynamics. The analysis of chemogenomic data revealed that Sfh2 is involved in vesicle formation/transport and, potentially, in the endosome/trans-Golgi network (TGN) system in response to perturbed lipid metabolism under nutrient deprived conditions. The identification of its secondary ligand as squalene implies that squalene is acting as metabolic information to be translated into a phosphoinositide signal and a specific cellular function; according to the Sec14-based model of PITP function. Finally, the data demonstrates that Sfh2 ligand-binding abilities can be uncoupled. However, better ligand-binding mutants need to be designed before the canonical heterotypic ligand exchange model can be validated in vivo. This final aim will establish that squalene metabolism is indeed coupled to PIP synthesis and vesicle transport by Sfh2. | en |
