Stress within the endoplasmic reticulum (ER) induces a coordinated response, namely the unfolded protein response (UPR), devoted to helping the ER cope with the accumulation of misfolded proteins. Failure of the UPR plays an important role in several human diseases. Recent studies report that intracellular accumulation of saturated fatty acids (SFAs) and cholesterol, seen in diseases of high incidence, such as obesity or atherosclerosis, results in ER stress. In the present study, we evaluated the effects of perturbations to lipid homeostasis on ER stress/UPR induction in the model eukaryote Saccharomyces cerevisiae. We show that SFA originating from either endogenous (preclusion of fatty acid desaturation) or exogenous (feeding with extracellular SFA) sources trigger ER stress and that ergosterol, the major sterol in yeast, acts synergistically with SFA in this process. This latter effect is connected to ergosterol accumulation within microsomal fractions from SFA-accumulating cells, which display highly saturated phospholipid content. Moreover, treating the cells with the molecular chaperone 4-phenyl butyrate abolishes UPR induction, suggesting that lipid-induced ER stress leads to an overload of misfolded protein that acts, in turn, as the molecular signal for induction of the UPR. The present data are discussed in the context of human diseases that involve lipid deregulation.

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A three-step method was developed for the purification of mesentericin Y105 (60% yield) from the culture supernatant of Leuconostoc mesenteroides Y105. The same procedure was successfully applied to the purification of five other anti-Listeria bacteriocins identified by mass spectrometry. Specific activities of the purified bacteriocins were compared.The increasing numbers of food contaminations by Listeria spp. have greatly stimulated research on class IIa bacteriocins produced by lactic acid bacteria. The number of such peptidic compounds may be limited since many of the newly detected strains express previously described bacteriocins. Consequently, the detection and characterization of still-unknown antagonistic peptides is becoming difficult. One of the more time-consuming steps in such studies is the purification of antagonistic compounds. Because bacteriocins are secreted into the culture medium, most strategies start with a step to concentrate bacteriocins from the culture supernatant, such as pH-dependent adsorption of bacteriocins on heat-killed producer bacteria (7), diatomite calcium silicate (Micro-Cel) (9), or rice hull ash or precipitation with silicic acid (19), ammonium sulfate (7), or ethanol (31). Although these procedures are used principally to reduce the working volume, they typically do not provide a high degree of purity. Therefore, subsequent steps of preparative isoelectric focusing (31) and/or multiple chromatographic separations, including cation exchange (7, 10, 22), gel filtration (12, 22), hydrophobic interaction (7,10,22), and reverse-phase liquid chromatography (6,10,22,24), are necessary to achieve significant purification of the bacteriocins. Usually, but not always, the protein yields obtained are low (for a review, see reference 7). This is probably due to the high number of steps in the protocol, leading to time-consuming processes and subsequently low yields.The primary structures of anti-Listeria bacteriocins are presented in Fig. 1. All of these peptides are characterized by the consensus sequence YGNGV(n)C(n) 4 C(n)V(n) 4 A (where n is any amino acid). More generally, the first 20 residues are well conserved, while a hydrophobic C-terminal half moiety is characterized by a large structural diversity, suggesting its implication in host specificity (11). We hypothesize that these variable C-terminal parts of the peptides result in differences in their specific anti-Listeria activities. Indeed, the sensitivity of a particular target strain depends on the bacteriocin concentration of the solution or culture supernatant used for the activity assay. Therefore, the host specificity described for a bacteriocin could depend on host sensitivity. Moreover, comparison of the bacteriocin specific activities described in the literature remains difficult because the methods and the target strains used are heterogeneous.Mesentericin Y105, a 37-amino-acid-long peptide produced by Leuconostoc mesenteroides Y105 was first characterized by Héchard et al. in 1992 (17). The method used to puri...