Crosstalk Between Osmolytes and Cellular Chaperones: Examples in Saccharomyces cerevisiae
Osmolytes and chaperones form two distinct arms of the cellular proteostasis network. They help the cell in adapting to a variety of stress conditions including changes in temperature, salinity, pH, redox balance, nutrient deprivation, etc. Osmolytes, also called compatible solutes, like disaccharides, amino acids and derivatives, are produced in the cell in response to stress and help stabilize proteins by a number of different mechanisms. Some of the chaperones and chaperonins perform basal functions in the cell, but their major role lies in protecting proteins and other biomolecules during stress conditions. They mainly comprise of heat shock proteins (Hsps) controlled by the heat shock factor (Hsf), various isomerases and other protein folding aids. The baker’s yeast Saccharomyces cerevisiae has been widely adopted as a model for higher organisms. Several of the biological pathways related to cellular stress response machinery are strongly conserved between yeast and humans, and yeast provides an excellent model to study proteotoxicity. Glycerol and trehalose are the major osmolytes whose levels are elevated in stressed yeast cells. The correlation between levels of compatible solutes and molecular chaperones under stress conditions has been studied extensively in yeast and has raised many interesting questions. A key issue is whether trehalose itself acts as the cytoprotectant or if the trehalose synthetic enzyme, Tps1, provides this function. The parallel relation between thermotolerance, trehalose and the protein remodelling factor Hsp104 observed in many cases has pointed to a complex association between the molecular and pseudo-chaperones. This chapter discusses some of these observations and attempts to provide a rational explanation of the interaction between the different components of the cellular stress response machinery using the budding yeast as a model system.
KeywordsChaperones Glycerol Heat shock proteins Osmolytes Saccharomyces cerevisiae Trehalose Unfolded protein response
Work in authors’ lab was supported by the Department of Biotechnology and Science and Engineering Research Board. ARP and ED acknowledge the award of junior research fellowships by NIPER S.A.S. Nagar and Department of Biotechnology (Govt. of India), respectively.