Alterations in protein synthesis and levels of heat shock 70 proteins in response to salt stress of the halotolerant yeast Rhodotorula mucilaginosa

Abstract

Responses of the halotolerant yeast Rhodotorula mucilaginosa YRH2 to salt stress was studied. Strain YRH2 was isolated from chemical industry park wastewater evaporation ponds that are characterized by large fluctuations in salinity and pH. Upon shift to high salt medium there is a shutdown of protein synthesis. Radiolabeling and separation of proteins from salt stressed and non-stressed cells identified down-regulated heat shock 70 proteins Ssb1/2p, by N-terminal sequencing and Western blotting. Ssb's role in salt stress in both R. mucilaginosa and S. cerevisiae was examined and we show that its response to salt stress and amino acid limitation is similar. Other proteins such as the heat shock 70 protein Kar2p/BiP and Protein Disulfide Isomerase were strongly induced in response to a shift to high salt in R. mucilaginosa and reacted in a manner similar to the effect of tunicamycin, a known unfolded protein response inducer. Also, assaying carboxypeptidase Y, we showed that high salt medium reduces the specific activity of the enzyme in R. mucilaginosa. It is suggested that the changes in the expression of the heat shock 70 proteins is a part of a mechanism which alleviates the damaging effects of high salt on protein folding in the yeast Rhodotorula mucilaginosa.

The response to unfolded protein is involved in osmotolerance of Pichia pastoris

“…Furthermore, intracellular levels of trehalose were analyzed as trehalose is thought to be involved in relieving or impeding protein folding stress [27], which may also occur during salt stress [9]. Intracellular trehalose levels were in the same range as glycerol levels but showed a significant trend ( p ≤ 0.05) towards decreased concentrations at medium and high osmolarity growth conditions in the wt strain but slightly missed the threshold p -value in the 3H6 Fab expressing strain (Figure 1C and Additional file 1)…”

“…In batch culture, osmotic shock usually implies a temporary growth arrest to adapt the cellular metabolism [7]. Major adjustments of gene transcription in Saccharomyces cerevisiae and other yeasts include the induction of glycerol-3-phosphate dehydrogenase GPD1 transcription [8], transcriptional repression of the plasma membrane glycerol efflux channel FPS1 [2], but also the adjustment of ribosome biogenesis and the translation and protein folding machinery [9]. Glycerol production, but also the production of other small organic molecules, is induced in different yeast species to compensate variations of osmotic conditions [10].…”

Salinity-Induced Palmella Formation Mechanism in Halotolerant Algae Dunaliella salina Revealed by Quantitative Proteomics and Phosphoproteomics

“…CALR is involved in the folding and quality control of newly synthesized proteins and glycoproteins, which is highly conserved and crucial for plant development and stress response (Garg et al, 2015). In addition, protein disulfide isomerase aids in the formation of proper disulfide bonds during protein folding in the endoplasmic reticulum (Appenzeller-Herzog and Ellgaard, 2008), which were salinity-increased in salt-tolerant Medicago sativa (Rahman et al, 2015), barley (Mostek et al, 2015), rice (Ghaffari et al, 2014), and halotolerant yeast ( Rhodotorula mucilaginosa ) (Lahav et al, 2004). Additionally, luminal binding protein Bip1 functions in precursor protein import and translocation (Wang et al, 2004b), which was high salt-induced in halotolerant yeast (Lahav et al, 2004).…”

Yeast translational response to high salinity: Global analysis reveals regulation at multiple levels

“…High salinity stress affects cellular physiology at multiple levels: it creates a hyperosmotic force that leads to water efflux and consequently to loss of internal pressure (Hohmann 2002); it imbalances membrane potential and thereby affects the activity of membrane transporters (Norbeck and Blomberg 1998); it disrupts ion homeostasis within cells and intracellular pH equilibrium, which result in misfolding of proteins and the generation of reactive oxygen species (ROS) (Mendoza et al 1994;Lahav et al 2004;Koziol et al 2005;Mortensen et al 2006); finally, it causes a solute-specific toxic effect. For example, sodium or lithium ions, but not potassium, inhibit the phosphatase activity of Hal2p and, thus, reduce the ability of cells to resist high salinity (Murguia et al 1995(Murguia et al , 1996.…”