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In some pathogens, trehalose biosynthesis is induced in response to stress as a protection mechanism. This pathway is an attractive target for antimicrobials as neither the enzymes, Tps1, and Tps2, nor is trehalose present in humans. Accumulation of T6P in Candida albicans, achieved by deletion of TPS2, resulted in strong reduction of fungal virulence. In this work, the effect of T6P on Tps1 activity was evaluated. Saccharomyces cerevisiae, C. albicans, and Candida tropicalis were used as experimental models. As expected, a heat stress induced both trehalose accumulation and increased Tps1 activity. However, the addition of 125 μM T6P to extracts obtained from stressed cells totally abolished or reduced in 50 and 60 % the induction of Tps1 activity in S. cerevisiae, C. tropicalis, and C. albicans, respectively. According to our results, T6P is an uncompetitive inhibitor of S. cerevisiae Tps1. This kind of inhibitor is able to decrease the rate of reaction to zero at increased concentrations. Based on the similarities found in sequence and function between Tps1 of S. cerevisiae and some pathogens and on the inhibitory effect of T6P on Tps1 activity observed in vitro, novel drugs can be developed for the treatment of infectious diseases caused by organisms whose infectivity and survival on the host depend on trehalose.

The fermentation process offers a wide variety of stressors for yeast, such as temperature, aging, and ethanol. To evaluate a possible beneficial effect of trehalose on ethanol production, we used mutant strains of Saccharomyces cerevisiae possessing different deficiencies in the metabolism of this disaccharide: in synthesis, tps1; in transport, agt1; and in degradation, ath1 and nth1. According to our results, the tps1 mutant, the only strain tested unable to synthesize trehalose, showed the lowest fermentation yield, indicating that this sugar is important to improve ethanol production. At the end of the first fermentation cycle, only the strains deficient in transport and degradation maintained a significant level of the initial trehalose. The agt1, ath1, and nth1 strains showed the highest survival rates and the highest proportions of non-petites. Accumulation of petites during fermentation has been correlated to low ethanol production. When recycled back for a subsequent fermentation, those mutant strains produced the highest ethanol yields, suggesting that trehalose is required for improving fermentative capacity and longevity of yeasts, as well as their ability to withstand stressful industrial conditions. Finally, according to our results, the mechanism by which trehalose improves ethanol production seems to involve mainly protection against protein oxidation., (© Springer-Verlag 2011)

During menadione stress, trehalose was necessary intracellularly, but under H2O2, the sugar was required on the outside of the plasma membrane. The mechanism of protection involves minimizing the oxidative damage caused to both proteins and lipids, which would require the presence of trehalose on both sides of the lipid bilayer.

Aiming to focus the protective role of the sugar trehalose under oxidative conditions, two sets of Saccharomyces cerevisiae strains, having different profiles of trehalose synthesis, were used. Cells were treated either with a 10% trehalose solution or with a heat treatment (which leads to trehalose accumulation) and then exposed either to menadione (a source of superoxide) or to tert-butylhydroperoxide (TBOOH). According to our results, trehalose markedly increased viability upon exposure to menadione stress, which seems to be correlated with decrease in lipid peroxidation levels. The protective effect of trehalose against oxidative damage produced by menadione was especially efficient under SOD1 deficiency. On the other hand, this sugar does not seem to participate of the mechanism of acquisition of tolerance against TBOOH, since trehalose pretreatment (addition of external trehalose) was not capable of increase cell survival. Therefore, trehalose plays a role in protecting cells, especially membranes, from oxidative injuries. However, this mechanism of defense is dependent on the type of oxidative stress to which cells are submitted.

Previous studies on the resistance of yeast cells to dehydration pointed towards the protective role of trehalose and the importance of the specific trehalose transporter in guaranteeing survival. The present report demonstrates that the trehalose transporter is essential during the germination process in order to translocate trehalose from the cytosol to the external environment. Diploids that lack the trehalose transporter germinate poorly and do not form 4 spore tetrads although they accumulate trehalose and show trehalase activity. Furthermore, addition of exogenous trehalose to the germination medium enhances germination and normal segregation. The ability to transport trehalose is dominant and seems to be related to a single gene.

Cells of a heat-shock resistant mutant were approximately 1000-times more resistant to lethal heat shock than those of the parental strain. We observed that exponentially growing cells of the mutant synthesized trehalose and showed increased osmotolerance, dehydration tolerance an ethanol tolerance, a fact not observed in wild type strains. The mutant synthesizes constitutively six proteins, among them two proteins of 56 and 63 kDa. Interestingly these molecular weights could correspond to the subunit of trehalose-6-phosphate synthase and to phosphoglucomutase II, respectively. Our results showed that glucose-growing cells of the hsr 1 mutant possessed high levels of activity of these enzymes when compared to the control strain.

Yeast cells accumulate the disaccharide trehalose in response to certain stress conditions. In an attempt to verify the role that trehalose plays when yeast cells are faced with heat stress, yeast mutant strains with specific lesions in trehalose metabolism were used. Cultures growing exponentially on glucose were shifted from 28 to 40 degrees C for 1 h. Accumulation of trehalose was correlated with heat tolerance, measured as resistance to 50.5 degrees C. Additionally, it was observed that the trehalose carrier was not involved in the mechanism of thermotolerance acquisition. Mutants that lack the carrier were also able to acquire thermotolerance as long as synthesis of the disaccharide took place.

Yeast cells are well known for their ability to survive complete dehydration, a phenomenon that is directly linked to the presence of the sugar trehalose in these cells. This sugar apparently endows the cells with the capacity to survive dehydration. Previous studies on in vitro models showed that trehalose must be present on both sides of the bilayer to stabilize dry membranes. The present report demonstrates that a specific trehalose carrier seems to enable the sugar to protect the yeast cell membrane by translocating trehalose from the cytosol to the extracellular environment. Saccharomyces cerevisiae mutant strains which lack the trehalose carrier did not survive after dehydration although they accumulated endogenous trehalose. Furthermore, when carrier mutants were dehydrated in the presence of exogenous trehalose the cells became more resistant showing increased survival.