Sfh3 is a sterol-modulated PI/PI4P transfer protein that confers azole resistance in yeast by specifically mediating lanosterol/PI exchange

Abstract

Lipid transfer proteins precisely distribute lipids within eukaryotic cells, supporting functions such as vesicular trafficking and cellular signaling. Here, we analyzed whether Sfh3 (Sec14 homolog 3) functions as a sterol/phosphatidylinositol (PI) exchanger to clarify its role in neutral lipid mobilization from lipid droplets and in azole resistance in yeast. Using real-time assays, we found that its ergosterol transfer capacity is not activated by PI and is inhibited by ergosterol biosynthesis intermediates, such as lanosterol. Next, we found that Sfh3 exhibits both PI and PI4P transfer activities, which sterols can modulate. Through kinetic, structure-function, and thermal stability analyses, we identified remarkable Sfh3 mutants and ranked Sfh3's relative affinity for its lipid ligands. This allowed us to show that Sfh3 performs selective lanosterol/PI exchange, provided it recognizes PI, in the presence of ergosterol, and that this activity is necessary for yeast resistance to miconazole. Collectively, our data show that Sfh3 is a sterol-regulated PI/PI4P transfer protein, potentially linking sterol metabolism and PI4P signaling during lipid droplet utilization. In azole-treated yeast, elevated lanosterol levels may shift Sfh3 into an exclusive PI/lanosterol exchange mode, promoting cellular detoxification and conferring drug resistance. By revealing unanticipated Sfh-mediated lipid transfer mechanisms, our study provides new insights into the Sec14 family.