In the unfolded protein response (UPR) signaling pathway, accumulation of unfolded proteins in the endoplasmic reticulum (ER) activates a transmembrane kinase/ribonuclease Ire1, which causes the transcriptional induction of ER-resident chaperones, including BiP/Kar2. It was previously hypothesized that BiP/Kar2 plays a direct role in the signaling mechanism. In this model, association of BiP/Kar2 with Ire1 represses the UPR pathway while under conditions of ER stress, BiP/Kar2 dissociation leads to activation. To test this model, we analyzed five temperature-sensitive alleles of the yeast KAR2 gene. When cells carrying a mutation in the Kar2 substrate-binding domain were incubated at the restrictive temperature, association of Kar2 to Ire1 was disrupted, and the UPR pathway was activated even in the absence of extrinsic ER stress. Conversely, cells carrying a mutation in the Kar2 ATPase domain, in which Kar2 poorly dissociated from Ire1 even in the presence of tunicamycin, a potent inducer of ER stress, were unable to activate the pathway. Our findings provide strong evidence in support of BiP/Kar2-dependent Ire1 regulation model and suggest that Ire1 associates with Kar2 as a chaperone substrate. We speculate that recognition of unfolded proteins is based on their competition with Ire1 for binding with BiP/Kar2.

Coffee is one of the most consumed beverages in the world, and its popularity has prompted the necessity to constantly increase the variety and improve the characteristics of coffee as a general commodity. The popularity of coffee as a staple drink has also brought undesired side effects, since coffee production, processing and consumption are all accompanied by impressive quantities of coffee-related wastes which can be a threat to the environment. In this review, we integrated the main studies on fermentative yeasts used in coffee-related industries with emphasis on two different directions: (1) the role of yeast strains in the postharvest processing of coffee, the possibilities to use them as starting cultures for controlled fermentation and their impact on the sensorial quality of processed coffee, and (2) the potential to use yeasts to capitalize on coffee wastes—especially spent coffee grounds—in the form of eco-friendly biomass, biofuel or fine chemical production.

The Ca²⁺‐dependent response to oxidative stress caused by H₂O₂ or tert‐butylhydroperoxide (tBOOH) was investigated in Saccharomyces cerevisiae cells expressing transgenic cytosolic aequorin, a Ca²⁺‐dependent photoprotein. Both H₂O₂ and tBOOH induced an immediate and short‐duration cytosolic Ca²⁺ increase that depended on the concentration of the stressors. Sublethal doses of H₂O₂ induced Ca²⁺ entry into the cytosol from both extracellular and vacuolar sources, whereas lethal H₂O₂ shock mobilized predominantly the vacuolar Ca²⁺. Sublethal and lethal tBOOH shocks induced mainly the influx of external Ca²⁺, accompanied by a more modest vacuolar contribution. Ca²⁺ transport across the plasma membrane did not necessarily involve the activity of the Cch1p/Mid1p channel, whereas the release of vacuolar Ca²⁺ into the cytosol required the vacuolar channel Yvc1p. In mutants lacking the Ca²⁺ transporters, H₂O₂ or tBOOH sensitivity correlated with cytosolic Ca²⁺ overload. Thus, it appears that under H₂O₂‐induced or tBOOH‐induced oxidative stress, Ca²⁺ mediates the cytotoxic effect of the stressors and not the adaptation process.

Homocysteine (Hcy), a sulfur amino acid, is the only direct precursor for L-methionine synthesis through a reaction that requires vitamin B₁₂, representing a connection with "one-carbon" units metabolism. Hcy catabolism requires vitamin B₆ and as a consequence, alteration in folic acid and B vitamins status impairs Hcy biotransformation. Numerous studies have indicated that Hcy is an independent risk factor for cardio- and cerebrovascular diseases. In the last decade, several clinical trials have investigated the possible correlation between the use of folic acid and vitamins B₆ and B₁₂ for lowering Hcy plasma concentration and the reduced risk of stroke or its recurrence. This review is aimed to present some aspects of Hcy biochemistry, as well as the mechanisms through which it exerts the toxic effects on the vascular endothelium. We also discuss the results of some of the clinical trials developed to investigate the beneficial effects of vitamin therapy in the prevention and management of stroke.