RESUMEN
Cellular organelles maintain areas of close apposition with other organelles at which the cytosolic gap in between them is reduced to a minimum. These membrane contact sites (MCS) are vital for organelle communication and are formed by molecular tethers that physically connect opposing membranes. Although many regulatory pathways are known to converge at MCS, a link between MCS and transcriptional regulation-the primary mechanism through which cells adapt their metabolism to environmental cues-remains largely elusive. In this study, we performed RNA-sequencing on Saccharomyces cerevisiae cells lacking tricalbin proteins (Tcb1, Tcb2, Tcb3), a family of tethering proteins that connect the endoplasmic reticulum with the plasma membrane and Golgi, to investigate if gene expression is altered when MCS are disrupted. Our results indicate that in the tcb1Δ2Δ3Δ strain, pathways responsive to a high-glucose environment, including glycolysis, fermentation, amino acid synthesis, and low-affinity glucose uptake, are upregulated. Conversely, pathways crucial during glucose depletion, such as the tricarboxylic acid (TCA) cycle, respiration, high-affinity glucose uptake, and amino acid uptake are downregulated. In addition, we demonstrate that the altered gene expression of tcb1Δ2Δ3Δ in glucose metabolism correlates with increased growth, glucose consumption, CO2 production, and ethanol generation. In conclusion, our findings reveal that tricalbin protein deletion induces a shift in gene expression patterns mimicking cellular responses to a high-glucose environment. This suggests that MCS play a role in sensing and signaling pathways that modulate gene transcription in response to glucose availability.
RESUMEN
The transport of ceramide from the endoplasmic reticulum (ER) to the Golgi is a key step in the synthesis of complex sphingolipids, the main building blocks of the plasma membrane. In yeast, ceramide is transported to the Golgi either through ATP-dependent COPII vesicles of the secretory pathway or by ATP-independent non-vesicular transport that involves tethering proteins at ER-Golgi membrane contact sites. Studies in both mammalian and yeast cells reported that vesicular transport mainly carries ceramide containing very long chain fatty acids, while the main mammalian non-vesicular ceramide transport protein CERT only transports ceramides containing short chain fatty acids. However, if non-vesicular ceramide transport in yeast similarly favors short chain ceramides remained unanswered. Here we employed a yeast GhLag1 strain in which the endogenous ceramide synthase is replaced by the cotton-derived GhLag1 gene, resulting in the production of short chain C18 rather than C26 ceramides. We show that block of vesicular transport through ATP-depletion or the use of temperature-sensitive sec mutants caused a reduction in inositolphosphorylceramide (IPC) synthesis to similar extent in WT and GhLag1 backgrounds. Since the remaining IPC synthesis is a readout for non-vesicular ceramide transport, our results indicate that non-vesicular ceramide transport is neither blocked nor facilitated when only short chain ceramides are present. Therefore, we propose that the sorting of ceramide into non-vesicular transport is independent of acyl chain length in budding yeast.
Asunto(s)
Ceramidas , Aparato de Golgi , Saccharomyces cerevisiae , Ceramidas/metabolismo , Aparato de Golgi/metabolismo , Transporte Biológico , Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/genética , Saccharomycetales/metabolismo , Saccharomycetales/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Retículo Endoplásmico/metabolismo , Adenosina Trifosfato/metabolismo , GlicoesfingolípidosRESUMEN
Membrane contact sites (MCSs) are junctures that perform important roles including coordinating lipid metabolism. Previous studies have indicated that vacuolar fission/fusion processes are coupled with modifications in the membrane lipid composition. However, it has been still unclear whether MCS-mediated lipid metabolism controls the vacuolar morphology. Here, we report that deletion of tricalbins (Tcb1, Tcb2, and Tcb3), tethering proteins at endoplasmic reticulum (ER)-plasma membrane (PM) and ER-Golgi contact sites, alters fusion/fission dynamics and causes vacuolar fragmentation in the yeast Saccharomyces cerevisiae. In addition, we show that the sphingolipid precursor phytosphingosine (PHS) accumulates in tricalbin-deleted cells, triggering the vacuolar division. Detachment of the nucleus-vacuole junction (NVJ), an important contact site between the vacuole and the perinuclear ER, restored vacuolar morphology in both cells subjected to high exogenous PHS and Tcb3-deleted cells, supporting that PHS transport across the NVJ induces vacuole division. Thus, our results suggest that vacuolar morphology is maintained by MCSs through the metabolism of sphingolipids.
Asunto(s)
Membranas Mitocondriales , Proteínas de Saccharomyces cerevisiae , Membranas Mitocondriales/metabolismo , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Vacuolas/metabolismo , Esfingolípidos/metabolismo , Metabolismo de los Lípidos , Membrana Celular/metabolismoRESUMEN
Cells sense and control the number and quality of their organelles, but the underlying mechanisms of this regulation are not understood. Our recent research in the yeast Saccharomyces cerevisiae has shown that long acyl chain ceramides in the endoplasmic reticulum (ER) membrane and the lipid moiety of glycosylphosphatidylinositol (GPI) anchor determine the sorting of GPI-anchored proteins in the ER. Here, we show that a mutant strain, which produces shorter ceramides than the wild-type strain, displays a different count of Golgi cisternae. Moreover, deletions of proteins that remodel the lipid portion of GPI anchors resulted in an abnormal number of Golgi cisternae. Thus, our study reveals that protein sorting in the ER plays a critical role in maintaining Golgi biogenesis.
Asunto(s)
Proteínas de Saccharomyces cerevisiae , Saccharomycetales , Saccharomycetales/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Retículo Endoplásmico/metabolismo , Aparato de Golgi/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Transporte de Proteínas , Ceramidas/metabolismo , Glicosilfosfatidilinositoles/metabolismoRESUMEN
Liquid-ordered (Lo) membrane domains have been proposed to play important roles in a wide variety of biological processes, such as protein sorting and cell signaling. However, the mechanisms by which they are formed and maintained remain poorly understood. Lo domains are formed in the vacuolar membrane of yeast in response to glucose starvation. Here, we show that the deletion of proteins that localize to vacuole membrane contact sites (MCSs) caused a marked decrease in the number of cells with Lo domains. In addition to Lo domain formation, autophagy is induced upon glucose starvation. However, the deletion of core autophagy proteins did not inhibit Lo domain formation. Thus, we propose that vacuolar Lo domain formation during glucose restriction is regulated by MCSs but not by autophagy.
Asunto(s)
Proteínas de Saccharomyces cerevisiae , Vacuolas , Vacuolas/metabolismo , Glucosa/metabolismo , Membranas Mitocondriales/metabolismo , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMEN
Glycosylphosphatidylinositol-anchored proteins (GPI-APs) exit the endoplasmic reticulum (ER) through a specialized export pathway in the yeast Saccharomyces cerevisiae. We have recently shown that a very-long acyl chain (C26) ceramide present in the ER membrane drives clustering and sorting of GPI-APs into selective ER exit sites (ERES). Now, we show that this lipid-based ER sorting also involves the C26 ceramide as a lipid moiety of GPI-APs, which is incorporated into the GPI anchor through a lipid-remodeling process after protein attachment in the ER. Moreover, we also show that a GPI-AP with a C26 ceramide moiety is monitored by the GPI-glycan remodelase Ted1, which, in turn, is required for receptor-mediated export of GPI-APs. Therefore, our study reveals a quality-control system that ensures lipid-based sorting of GPI-APs into selective ERESs for differential ER export, highlighting the physiological need for this specific export pathway.
Asunto(s)
Ceramidas , Retículo Endoplásmico , Ceramidas/metabolismo , Retículo Endoplásmico/metabolismo , Proteínas Ligadas a GPI/metabolismo , Glicosilfosfatidilinositoles/metabolismo , Transporte de Proteínas , Saccharomyces cerevisiae/metabolismoRESUMEN
Sphingolipids are the most diverse class of membrane lipids, in terms of their structure and function. Structurally simple sphingolipid precursors, such as ceramides, act as intracellular signaling molecules in various processes, including apoptosis, whereas mature and complex forms of sphingolipids are important structural components of the plasma membrane. Supplying complex sphingolipids to the plasma membrane, according to need, while keeping pro-apoptotic ceramides in check is an intricate task for the cell and requires mechanisms that tightly control sphingolipid synthesis, breakdown, and storage. As each of these processes takes place in different organelles, recent studies, using the budding yeast Saccharomyces cerevisiae, have investigated the role of membrane contact sites as hubs that integrate inter-organellar sphingolipid transport and regulation. In this review, we provide a detailed overview of the findings of these studies and put them into the context of established regulatory mechanisms of sphingolipid homeostasis. We have focused on the role of membrane contact sites in sphingolipid metabolism and ceramide transport, as well as the mechanisms that prevent toxic ceramide accumulation.
RESUMEN
Glycosylphosphatidylinositol (GPI) anchoring of proteins is an essential post-translational modification in all eukaryotes that occurs at the endoplasmic reticulum (ER) and serves to deliver GPI-anchored proteins (GPI-APs) to the cell surface where they play a wide variety of vital physiological roles. This paper describes a specialized method for purification and structural analysis of the GPI glycan of individual GPI-APs in yeast. The protocol involves the expression of a specific GPI-AP tagged with GFP, enzymatic release from the cellular membrane fraction, immunopurification, separation by electrophoresis and analysis of the peptides bearing GPI glycans by mass spectrometry after trypsin digestion. We used specifically this protocol to address the structural remodeling that undergoes the GPI glycan of a specific GPI-AP during its transport to the cell surface. This method can be also applied to investigate the GPI-AP biosynthetic pathway and to directly confirm predicted GPI-anchoring of individual proteins.
Asunto(s)
Polisacáridos/química , Espectrometría de Masas en Tándem , Retículo Endoplásmico/metabolismo , Proteínas Ligadas a GPI/química , Proteínas Ligadas a GPI/metabolismo , Péptidos/química , Péptidos/metabolismo , Saccharomyces cerevisiae/metabolismoRESUMEN
Sphingolipid biosynthesis occurs in both the endoplasmic reticulum (ER) and the Golgi apparatus. Ceramide synthesized in the ER is transported to the Golgi and incorporated into complex sphingolipids. Here, we present a step-by-step protocol to analyze sphingolipid metabolism in budding yeast. Ceramide and inositolphosphorylceramide (IPC) are classes of sphingolipids present in yeast and are metabolically labeled with radioactive precursors. This protocol for metabolic labeling can be used to investigate ceramide transport in an in vivo environment. For complete details on the use and execution of this protocol, please refer to Ikeda et al. (2020).
Asunto(s)
Técnicas Citológicas/métodos , Saccharomycetales , Esfingolípidos , Ceramidas/análisis , Ceramidas/química , Ceramidas/aislamiento & purificación , Ceramidas/metabolismo , Fraccionamiento Químico/métodos , Cromatografía en Capa Delgada/métodos , Glicoesfingolípidos/análisis , Glicoesfingolípidos/química , Glicoesfingolípidos/aislamiento & purificación , Glicoesfingolípidos/metabolismo , Saccharomycetales/química , Saccharomycetales/metabolismo , Esfingolípidos/análisis , Esfingolípidos/química , Esfingolípidos/aislamiento & purificación , Esfingolípidos/metabolismo , Coloración y EtiquetadoRESUMEN
Cell division produces two viable cells of a defined size. Thus, all cells require mechanisms to measure growth and trigger cell division when sufficient growth has occurred. Previous data suggest a model in which growth rate and cell size are mechanistically linked by ceramide-dependent signals in budding yeast. However, the conservation of mechanisms that govern growth control is poorly understood. In fission yeast, ceramide synthase is encoded by two genes, Lac1 and Lag1. Here, we characterize them by using a combination of genetics, microscopy, and lipid analysis. We showed that Lac1 and Lag1 co-immunoprecipitate and co-localize at the endoplasmic reticulum. However, each protein generates different species of ceramides and complex sphingolipids. We further discovered that Lac1, but not Lag1, is specifically required for proper control of cell growth and size in Schizosaccharomyces pombe. We propose that specific ceramide and sphingolipid species produced by Lac1 are required for normal control of cell growth and size in fission yeast.
Asunto(s)
Oxidorreductasas/metabolismo , Subunidades de Proteína/metabolismo , Proteínas de Schizosaccharomyces pombe/metabolismo , Schizosaccharomyces/enzimología , Schizosaccharomyces/crecimiento & desarrollo , Esfingosina N-Aciltransferasa/metabolismo , Secuencia de Aminoácidos , Proliferación Celular , Secuencia Conservada , Retículo Endoplásmico/metabolismo , Lípidos/química , Modelos Biológicos , Oxidorreductasas/química , Subunidades de Proteína/química , Transporte de Proteínas , Esfingolípidos/metabolismoRESUMEN
Protein sorting in the secretory pathway is crucial to maintain cellular compartmentalization and homeostasis. In addition to coat-mediated sorting, the role of lipids in driving protein sorting during secretory transport is a longstanding fundamental question that still remains unanswered. Here, we conduct 3D simultaneous multicolor high-resolution live imaging to demonstrate in vivo that newly synthesized glycosylphosphatidylinositol-anchored proteins having a very long chain ceramide lipid moiety are clustered and sorted into specialized endoplasmic reticulum exit sites that are distinct from those used by transmembrane proteins. Furthermore, we show that the chain length of ceramide in the endoplasmic reticulum membrane is critical for this sorting selectivity. Our study provides the first direct in vivo evidence for lipid chain length-based protein cargo sorting into selective export sites of the secretory pathway.
Asunto(s)
Ceramidas , Retículo Endoplásmico , Ceramidas/metabolismo , Retículo Endoplásmico/metabolismo , Proteínas de la Membrana/metabolismo , Transporte de Proteínas , Vías SecretorasRESUMEN
Lipid composition varies among organelles, and the distinct lipid composition is important for specific functions of each membrane. Lipid transport between organelles, which is critical for the maintenance of membrane lipid composition, occurs by either vesicular or non-vesicular mechanisms. In yeast, ceramide synthesized in the endoplasmic reticulum (ER) is transported to the Golgi apparatus where inositolphosphorylceramide (IPC) is formed. Here we show that a fraction of Tcb3p, a yeast tricalbin protein, localizes to ER-Golgi contact sites. Tcb3p and their homologs Tcb1p and Tcb2p are required for formation of ER-Golgi contacts and non-vesicular ceramide transport. Absence of Tcb1p, Tcb2p, and Tcb3p increases acylceramide synthesis and subsequent lipid droplet (LD) formation. As LD can sequester excess lipids, we propose that tricalbins act as regulators of ceramide transport at ER-Golgi contact sites to help reduce a potentially toxic accumulation of ceramides.
RESUMEN
Deficiency of the endoplasmic reticulum transmembrane protein ARV1 leads to epileptic encephalopathy in humans and in mice. ARV1 is highly conserved, but its function in human cells is unknown. Studies of yeast arv1 null mutants indicate that it is involved in a number of biochemical processes including the synthesis of sphingolipids and glycosylphosphatidylinositol (GPI), a glycolipid anchor that is attached to the C-termini of many membrane bound proteins. GPI anchors are post-translational modifications, enabling proteins to travel from the endoplasmic reticulum (ER) through the Golgi and to attach to plasma membranes. We identified a homozygous pathogenic mutation in ARV1, p.Gly189Arg, in two brothers with infantile encephalopathy, and characterized the biochemical defect caused by this mutation. In addition to reduced expression of ARV1 transcript and protein in patients' fibroblasts, complementation tests in yeast showed that the ARV1 p.Gly189Arg mutation leads to deficient maturation of Gas1, a GPI-anchored protein, but does not affect sphingolipid synthesis. Our results suggest, that similar to mutations in other proteins in the GPI-anchoring pathway, including PIGM, PIGA, and PIGQ, ARV1 p.Gly189Arg causes a GPI anchoring defect and leads to early onset epileptic encephalopathy.
Asunto(s)
Encefalopatías/genética , Proteínas Portadoras/genética , Glicosilfosfatidilinositoles/biosíntesis , Discapacidad Intelectual/genética , Proteínas de la Membrana/genética , Convulsiones/genética , Adolescente , Niño , Retículo Endoplásmico/metabolismo , Fibroblastos/metabolismo , Prueba de Complementación Genética , Aparato de Golgi/metabolismo , Homocigoto , Humanos , Lípidos/química , Masculino , Manosiltransferasas/genética , Mutación , Linaje , Dominios Proteicos , TemperaturaRESUMEN
Glycosylphosphatidylinositol (GPI) is synthesized in the endoplasmic reticulum (ER) and added onto proteins to form GPI-anchored proteins. Among the many proteins involved in this process, ACAT-related enzyme-2 required for viability 1 (Arv1) is a candidate, functioning as a flippase that translocates GPI intermediates from the cytoplasmic side into the luminal side of the ER membranes. Here, we show that the deletion of the ARV1 gene in yeast leads to cold-sensitive defects in cell growth and GPI anchor synthesis. Furthermore, complementation assays show that the overexpression of a missense human ARV1-G189R mutant does not completely restore the cold-sensitive phenotypes of the yeast arv1 mutant. Our results support the proposed role of Arv1 in GPI anchor synthesis and suggest that ARV1-linked human diseases result from defective GPI anchor synthesis.
Asunto(s)
Glicosilfosfatidilinositoles/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/metabolismo , Sustitución de Aminoácidos , Frío , Retículo Endoplásmico/genética , Retículo Endoplásmico/metabolismo , Glicosilfosfatidilinositoles/genética , Aparato de Golgi/genética , Aparato de Golgi/metabolismo , Membranas Intracelulares/metabolismo , Proteínas de la Membrana/genética , Mutación Missense , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/genéticaRESUMEN
Gamma-aminobutyric acid (GABA) is produced by Lactobacillus brevis using date residue fermentation. In this study, the GABA production method was improved, for which L. brevis strain JCM 1059T was the most efficient among the four L. brevis strains examined. This was presumably due to a difference in the expression level of the gene encoding glutamate decarboxylase that catalyzes GABA synthesis.Abbreviation: GABA: gamma-aminobutyric acid.
Asunto(s)
Glutamato Descarboxilasa/genética , Levilactobacillus brevis/enzimología , Levilactobacillus brevis/genética , Phoeniceae/química , Extractos Vegetales/metabolismo , Ácido gamma-Aminobutírico/metabolismo , Secuencia de Aminoácidos , Proteínas Bacterianas/metabolismo , Fermentación , Regulación Bacteriana de la Expresión Génica , Genes Bacterianos/genética , Glutamato Descarboxilasa/metabolismo , Concentración de Iones de Hidrógeno , ARN Ribosómico 16S/genética , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
The endoplasmic reticulum is the site of synthesis of most glycerophospholipids, neutral lipids and the initial steps of sphingolipid biosynthesis of the secretory pathway. After synthesis, these lipids are distributed within the cells to create and maintain the specific compositions of the other secretory organelles. This represents a formidable challenge, particularly while there is a simultaneous and quantitatively important flux of membrane components stemming from the vesicular traffic of proteins through the pathway, which can also vary depending on the cell type and status. To meet this challenge cells have developed an intricate system of interorganellar contacts and lipid transport proteins, functioning in non-vesicular lipid transport, which are able to ensure membrane lipid homeostasis even in the absence of membrane trafficking. Nevertheless, under normal conditions, lipids are transported in cells by both vesicular and non-vesicular mechanisms. In this review we will discuss the mechanism and roles of vesicular and non-vesicular transport of lipids from the ER to other organelles of the secretory pathway.
Asunto(s)
Retículo Endoplásmico/metabolismo , Metabolismo de los Lípidos , Animales , Transporte Biológico , Proteínas Portadoras/metabolismo , Homeostasis , Humanos , Vías Secretoras , Vesículas Transportadoras/metabolismoRESUMEN
Reduced ribosome biogenesis in response to environmental conditions is a key feature of cell adaptation to stress. For example, ribosomal genes are transcriptionally repressed when cells are exposed to tunicamycin, a protein glycosylation inhibitor that induces endoplasmic reticulum stress and blocks vesicular trafficking in the secretory pathway. Here, we describe a novel regulatory model, in which tunicamycin-mediated stress induces the accumulation of long-chain sphingoid bases and subsequent activation of Pkh1/2 signaling, which leads to decreased expression of ribosomal protein genes via the downstream effectors Pkc1 and Sch9. Target of rapamycin complex 1 (TORC1), an upstream activator of Sch9, is also required. This pathway links ribosome biogenesis to alterations in membrane lipid composition under tunicamycin-induced stress conditions. Our results suggest that sphingolipid/Pkh1/2-TORC1/Sch9 signaling is an important determinant for adaptation to tunicamycin-induced stress.
Asunto(s)
Estrés del Retículo Endoplásmico/efectos de los fármacos , Ribosomas/metabolismo , Saccharomyces cerevisiae/metabolismo , Transducción de Señal , Tunicamicina/farmacología , Proteínas Quinasas Dependientes de 3-Fosfoinosítido/metabolismo , Regulación Fúngica de la Expresión Génica , Proteínas Serina-Treonina Quinasas/metabolismo , Saccharomyces cerevisiae/efectos de los fármacos , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Esfingolípidos/metabolismo , Factores de Transcripción/metabolismo , Tunicamicina/toxicidadRESUMEN
Coat protein complex II (COPII) proteins form vesicles from the endoplasmic reticulum to export cargo molecules to the Golgi apparatus. Among the many proteins involved in this process, Sec12 is a key regulator, functioning as the guanosine diphosphate (GDP) exchange factor for Sar1p, the small guanosine triphosphatase (GTPase) that initiates COPII assembly. Here we show that overexpression of phospholipase B3 in the thermosensitive sec12-4 mutant partially restores growth and protein transport at non-permissive temperatures. Lipidomics analyses of these cells show a higher content of lysophosphatidylinositol (lysoPI), consistent with the lipid specificity of PLB3. Furthermore, we show that lysoPI is specifically enriched in COPII vesicles isolated from in vitro budding assays. As these results suggested that lysophospholipids could facilitate budding under conditions of defective COPII coat dynamics, we reconstituted COPII binding onto giant liposomes with purified proteins and showed that lysoPI decreases membrane rigidity and enhances COPII recruitment to liposomes. Our results support a mechanical facilitation of COPII budding by lysophospholipids.
Asunto(s)
Vesículas Cubiertas por Proteínas de Revestimiento/metabolismo , Lisofosfolípidos/metabolismo , Saccharomyces cerevisiae/metabolismo , Lisofosfolípidos/genética , Microsomas/metabolismoRESUMEN
Life is dependent on the protection of cellular functions from various stresses. Sphingolipids are essential biomembrane components in eukaryotic organisms, which are exposed to risks that may disrupt sphingolipid metabolism, threatening their lives. Defects of the sphingolipid biosynthesis pathway cause profound defects of various cellular functions and ultimately cell death. Therefore, cells are equipped with defense response mechanisms against aberrant metabolism of sphingolipids, the most characterized one being the target of rapamycin complex 2-mediated regulation of sphingolipid biosynthesis in budding yeast Saccharomyces cerevisiae. On the other hand, very recently, we found that the high osmolarity glycerol pathway is involved in suppression of a growth defect caused by a reduction in complex sphingolipid levels in yeast. It is suggested that this signaling pathway is not involved in the repair of the impaired biosynthesis pathway for sphingolipids, but compensates for cellular dysfunctions caused by reduction in complex sphingolipid levels. This is a novel protection mechanism against aberrant metabolism of complex sphingolipids, and further investigation of the mechanism will provide new insights into the physiological significance of complex sphingolipids. Here, we summarize the response signaling against breakdown of sphingolipid biosynthesis in yeast, which includes the high osmolarity glycerol pathway.
Asunto(s)
Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/metabolismo , Esfingolípidos/metabolismo , Ceramidas/metabolismo , Glicerol/metabolismo , Concentración Osmolar , Transducción de Señal , Esfingolípidos/biosíntesisRESUMEN
Dates are commercially consumed as semi-dried fruit or processed into juice and puree for further food production. However, the date residue after juice and puree production is not used, although it appears to be nutrient enriched. Here, date residue was fermented by a lactic acid bacterium, Lactobacillus brevis, which has been generally recognized as safe. Through degradation of sodium glutamate added to the residue during the fermentation, γ-aminobutyric acid (GABA), which reduces neuronal excitability, was produced at the conversion rate of 80-90% from glutamate. In order to achieve this GABA production level, pretreatment of the date residue with carbohydrate-degrading enzymes, i.e., cellulase and pectinase, was necessary. All ingredients used for this GABA fermentation were known as being edible. These results provide us with a solution for the increasing commercial demand for GABA in food industry with the use of date residue that has been often discarded.