Stress-driven structural and functional switching of Ypt1p from a GTPase to a molecular chaperone mediates thermo tolerance in Saccharomyces cerevisiae.

Guanosine triphosphatases (GTPases) function as molecular switches in signal transduction pathways that enable cells to respond to extracellular stimuli. Saccharomyces cerevisiae yeast protein two 1 protein (Ypt1p) is a monomeric small GTPase that is essential for endoplasmic reticulum-to-Golgi trafficking. By size-exclusion chromatography, SDS-PAGE, and native PAGE, followed by immunoblot analysis with an anti-Ypt1p antibody, we found that Ypt1p structurally changed from low-molecular-weight (LMW) forms to high-molecular-weight (HMW) complexes after heat shock. Based on our results, Ypt1p exhibited dual functions both as a GTPase and a molecular chaperone, and furthermore, heat shock induced a functional switch from that of a GTPase to a molecular chaperone driven by the structural change from LMW to HMW forms. Subsequently, we found, by using a galactose-inducible expression system, that conditional overexpression of YPT1 in yeast cells enhanced the thermotolerance of cells by increasing the survival rate at 55°C by ∼60%, compared with the control cells expressing YPT1 in the wild-type level. Altogether, our results suggest that Ypt1p is involved in the cellular protection process under heat stress conditions. Also, these findings provide new insight into the in vivo roles of small GTP-binding proteins and have an impact on research and the investigation of human diseases.