Glutathione S-transferase Ï´-subunit as a phenotypic suppressor of pmr1Δ strain, the Kluyveromyces lactis model for Hailey-Hailey disease.

BACKGROUND: Hailey-Hailey disease (HHD), also known as familial benign chronic pemphigus, is a rare, chronic and recurrent blistering disorder, histologically characterized by suprabasal acantholysis. HHD has been linked to mutations in ATP2C1, the gene encoding the human adenosine triphosphate (ATP)-powered calcium channel pump. METHODS: In this work, the genetically tractable yeast Kluyveromyces lactis has been used to study the molecular basis of Hailey-Hailey disease. The K. lactis strain depleted of PMR1, the orthologue of the human ATP2C1 gene, was used to screen a Madin-Darby canine kidney (MDCK) cDNA library to identify genetic interactors able to suppress the oxidative stress occurring in those cells. RESULTS: We have identified the Glutathione S-transferase Ï´-subunit (GST), an important detoxifying enzyme, which restores many of the defects associated with the pmr1Δmutant. GST overexpression in those cells suppressed the sensitivity to calcium chelating agents and partially re-established calcium (Ca2+) homeostasis by decreasing the high cytosolic Ca2+ levels in pmr1Δstrain. Moreover, we found that in the K. lactis mutant the mitochondrial dysfunction was suppressed by GST overexpression independently from calcineurin. In agreement with yeast results, a decreased expression of the human GST counterpart (GSTT1/M1) was observed in lesion-derived keratinocytes from HHD patients. CONCLUSIONS: These data highlighted the Glutathione S-transferase as a candidate gene associated with Hailey-Hailey disease. GENERAL SIGNIFICANCE: Kluyveromyces lactis can be considered a good model to study the molecular basis of this pathology.

13C NMR based profiling unveils different α-ketoglutarate pools involved into glutamate and lysine synthesis in the milk yeast Kluyveromyces lactis.

BACKGROUND: The construction of efficient cell factories for the production of metabolites requires the rational improvement/engineering of the metabolism of microorganisms. The subject of this paper is directed towards the quantitative understanding of the respiratory/fermentative Kluyveromyces lactis yeast metabolism and its rag8 casein kinase mutant, taken as a model for all rag gene mutations. METHODS: (13)C NMR spectroscopy and [1,2-(13)C2]glucose were used as metabolic stable-isotope tracer to define the metabolic profiling of a K. lactis yeast and its derivative mutants. RESULTS: Rag8 showed a decrease of all (13)C glutamate fractional enrichments, except for [4-(13)C]glutamate that was higher than wild type ones. A decrease of TCA cycle flux in rag8 mutants and a contribution of a [4-(13)C]ketoglutarate pool not originating from mitochondria were suggested. (13)C lysine enrichments confirmed the presence of two compartmentalized α-ketoglutarate (α-KG) pools participating to glutamate and lysine synthesis. Moreover, an increased transaldolase, as compared to transketolase activity, was observed in the rag8 mutant by (13)C NMR isotopomer analysis of alanine. CONCLUSIONS: (13)C NMR-based isotopomer analysis showed the existence of different α-KG metabolic pools for glutamate and lysine biosynthesis. In the rag8 mutant, (13)C labeled pentose phosphate intermediates participated in the synthesis of this compartmentalized α-KG pool. GENERAL SIGNIFICANCE: A compartmentalization of the α-KG pools involved in lysine biosynthesis has been revealed for the first time in K. lactis. Given its great impact in metabolic engineering field, its existence should be validated/compared with other yeasts and/or fungal species.

Depletion of casein kinase I leads to a NAD(P)(+)/NAD(P)H balance-dependent metabolic adaptation as determined by NMR spectroscopy-metabolomic profile in Kluyveromyces lactis.

BACKGROUND: In the Crabtree-negative Kluyveromyces lactis yeast the rag8 mutant is one of nineteen complementation groups constituting the fermentative-deficient model equivalent to the Saccharomyces cerevisiae respiratory petite mutants. These mutants display pleiotropic defects in membrane fatty acids and/or cell walls, osmo-sensitivity and the inability to grow under strictly anaerobic conditions (Rag(-) phenotype). RAG8 is an essential gene coding for the casein kinase I, an evolutionary conserved activity involved in a wide range of cellular processes coordinating morphogenesis and glycolytic flux with glucose/oxygen sensing. METHODS: A metabolomic approach was performed by NMR spectroscopy to investigate how the broad physiological roles of Rag8, taken as a model for all rag mutants, coordinate cellular responses. RESULTS: Statistical analysis of metabolomic data showed a significant increase in the level of metabolites in reactions directly involved in the reoxidation of the NAD(P)H in rag8 mutant samples with respect to the wild type ones. We also observed an increased de novo synthesis of nicotinamide adenine dinucleotide. On the contrary, the production of metabolites in pathways leading to the reduction of the cofactors was reduced. CONCLUSIONS: The changes in metabolite levels in rag8 showed a metabolic adaptation that is determined by the intracellular NAD(P)(+)/NAD(P)H redox balance state. GENERAL SIGNIFICANCE: The inadequate glycolytic flux of the mutant leads to a reduced/asymmetric distribution of acetyl-CoA to the different cellular compartments with loss of the fatty acid dynamic respiratory/fermentative adaptive balance response.

Biotreatment of Cr(VI) contaminated waters by sulphate reducing bacteria fed with ethanol.

Biological treatment of Cr(VI) contaminated waters was performed in fixed bed reactors inoculated with SRB (sulphate-reducing bacteria) growing on ethanol. Treatment efficiency was evaluated by checking chemical abatement of Cr(VI) and by ecotoxicological tests using the nematode Caenorhabditis elegans. A preliminary comparison between ethanol and lactate was performed, denoting that using ethanol, the same values of final sulphate abatement were obtained. In addition ethanol showed to be a substrate more competitive than lactate in kinetic terms. Fixed bed column reactors were continuously fed with a solution containing sulphates (3 g L(-1)), ethanol (1.5 g L(-1)) and Cr(VI) (50 mg L(-1)). At steady state the column inoculated with SRB removed 65 ± 5% of sulphate and 95 ± 5% of chromium. Bioactive removal mechanisms predominated over biosorption. Diminution of Cr(VI) toxicity was assessed by using the nematode C. elegans as a test organism showing that the survival of nematodes was 20% in the presence of the untreated influent and raised up to 53% when the nematodes were exposed to the treated effluent.

Complex multipathways alterations and oxidative stress are associated with Hailey-Hailey disease.

BACKGROUND: Hailey-Hailey disease (HHD) is an autosomal dominant disorder characterized by suprabasal cutaneous cell separation (acantholysis) leading to the development of erosive and oozing skin lesions. While a strong relationship exists between mutations in the gene that encodes the Ca(2+)/Mn(2+)-adenosine triphosphatase ATP2C1 and HHD, we still have little understanding of how these mutations affect manifestations of the disease. OBJECTIVES: This study was designed to determine early signalling events that affect epithelial cell growth and differentiation during HHD development. METHODS: Expression of key regulatory signals important for maintaining skin homeostasis were evaluated by Western blot analysis and by reverse transcriptase-polymerase chain reaction in primary keratinocytes obtained from skin biopsies of patients with HHD. Reactive oxygen species accumulation in primary keratinocytes derived from lesional skin of patients with HHD was assessed by dihydrorhodamine 123 (DHR) assay. RESULTS: HHD-derived keratinocytes showed downregulation of both Notch1 and differential regulation of different p63 isoforms. Itch and p63 are co-expressed in the epidermis and in primary keratinocytes where Itch controls the p63 protein steady-state level. We found that the Itch protein was significantly decreased in HHD-derived keratinocytes whereas the expression of its target, c-Jun, remained unaffected. We also found that HHD-derived keratinocytes undergo oxidative stress, which may explain both Notch1 and Itch downregulation. CONCLUSIONS: Our attempt to explore the molecular mechanism underlying HHD indicates a complex puzzle in which multi-hit combinations of altered signal pathways may explain the wide spectrum of defects in HHD.

Biotreatment and bioassessment of heavy metal removal by sulphate reducing bacteria in fixed bed reactors.

In this work a batch-optimised mixture (w/w %: 6% leaves, 9% compost, 3% Fe(0), 30% silica sand, 30% perlite, 22% limestone) was investigated in a continuous fixed bed column reactor for the treatment of synthetic acid-mine drainage (AMD). A column reactor was inoculated with sulphate-reducing bacteria and fed with a solution containing sulphate and heavy metals (As(V), Cd, Cr(VI), Cu and Zn). At steady state, sulphate abatement was 50+/-10%, while metals were totally removed. A degradation rate constant (k) of 0.015+/-0.001h(-1) for sulphate removal was determined from column data by assuming a first order degradation rate. Reduction of AMD toxicity was assessed by using the nematode Caenorhabditis elegans as a test organism. A lethality assay was performed with the toxicants before and after the treatment, showing that only 5% of the animals were still alive after 48h in presence of the contaminants, while the percentage increased to 73% when the nematodes were exposed to the solution eluted from the column.

SOD1, a new Kluyveromyces lactis helper gene for heterologous protein secretion.

Bottlenecks in protein expression and secretion often limit the development of industrial processes. By manipulating chaperone and foldase levels, improvements in yeast secretion were found for a number of proteins. Recently, sustained endoplasmic reticulum stress, occurring due to recombinant protein production, was reported to cause oxidative stress in yeast. Saccharomyces cerevisiae cells are able to trigger an adaptive response to oxidative-stress conditions, resulting in the upregulation of both primary and secondary antioxidant defenses. SOD1 encodes for a superoxide dismutase that catalyzes the dismutation of superoxide anions (O(2)(-)) into oxygen and hydrogen peroxide. It is a Cu(2+)/Zn(2+) metalloenzyme and represents an important antioxidant defense in nearly all aerobic and aerotolerant organisms. We found that overexpression of the Kluyveromyces lactis SOD1 (KlSOD1) gene was able to increase the production of two different heterologous proteins, human serum albumin (HSA) and glucoamylase from Arxula adeninivorans. In addition, KlSOD1 overexpression led to a significant decrease in the amount of reactive oxygen species (ROS) that originated during protein production. The yield of HSA also increased when K. lactis cells were grown in the presence of the antioxidant agent ascorbic acid and decreased when cells were challenged with menadione, a ROS generator compound. Moreover, we observed that, in high-osmolarity medium, cells overexpressing KlSOD1 showed higher growth rates than control cells. Our results thus further support the notion that the production of some heterologous proteins may be improved by manipulating genes involved in general stress responses.

The Kluyveromyces lactis CPY homologous genes: cloning and characterization of the KlPCL1 gene.

A 3.85-kb genomic fragment containing the KlPCL1 gene, with an open reading frame (ORF) of 1359 bp, was isolated from Kluyveromyces lactis genomic library by heterologous colony hybridization using the Saccharomyces cerevisiae PRC1 (ScPRC1) gene as a probe. The KlPCL1 nucleotide sequence was identical to the KLLAOC17490g ORF of K. lactis and showed >55 % identity with S. cerevisiae YBR139w and PRC1 genes encoding carboxypeptidases. The deduced KlPcl1p amino acid sequence displayed strong similarities to yeast and higher eukaryotic carboxypeptidases. In silico analyses revealed that KlPcl1p contained several highly conserved regions characteristic of the serine-type carboxypeptidases, such as the catalytic triad in the active site and the LNGGPGCSS, FHIAGESYAGHYIP and ICNWLGN motifs involved in the substrate binding. All this suggests that the KlPCL1 gene product belongs to the serine carboxypeptidase family. Sporulation and ascus dissection of a diploid strain heterozygous for single-copy disruption of KlPCL1 revealed that this gene is not essential in K. lactis. Further analyses of haploid and diploid deletion mutants demonstrated that disruption of the KlPCL1 gene neither impaired sporulation nor affected growth abilities of K. lactis cells under a variety of physiological conditions, e.g., growth on different carbon sources, at various temperatures or pH of the medium, and under nitrogen depletion.

APY-1, a novel Caenorhabditis elegans apyrase involved in unfolded protein response signalling and stress responses.

Protein glycosylation modulates a wide variety of intracellular events and dysfunction of the glycosylation pathway has been reported in a variety of human pathologies. Endo-apyrases have been suggested to have critical roles in protein glycosylation and sugar metabolism. However, deciphering the physiological relevance of Endo-apyrases activity has actually proved difficult, owing to their complexity and the functional redundancy within the family. We report here that a UDP/GDPase, homologous to the human apyrase Scan-1, is present in the membranes of Caenorhabditis elegans, encoded by the ORF F08C6.6 and hereinafter-named APY-1. We showed that ER stress induced by tunicamycin or high temperature resulted in increased transcription of apy-1. This increase was not observed in C. elegans mutants defective in ire-1 or atf-6, demonstrating the requirement of both ER stress sensors for up-regulation of apy-1. Depletion of APY-1 resulted in constitutively activated unfolded protein response. Defects in the pharynx and impaired organization of thin fibers in muscle cells were observed in adult worms depleted of APY-1. Some of the apy-1(RNAi) phenotypes are suggestive of premature aging, because these animals also showed accumulation of lipofuscin and reduced lifespan that was not dependent on the functioning of DAF-2, the receptor of the insulin/IGF-1 signaling pathway.

Characterization of the superoxide dismutase SOD1 gene of Kluyveromyces marxianus L3 and improved production of SOD activity.

Superoxide dismutase (SOD) activity is one major defense line against oxidative stress for all of the aerobic organisms, and industrial production of this enzyme is highly demanded. The Cu/Zn superoxide dismutase gene (KmSOD1) of Kluyveromyces marxianus L3 was cloned and characterized. The deduced KmSod1p protein shares 86% and 71% of identity with Kluyveromyces lactis and Saccharomyces cerevisiae Sod1p, respectively. The characteristic motifs and the amino acid residues involved in coordinating copper and zinc and in enzymatic function were conserved. To the aim of developing a microbial production of Cu/Zn superoxide dismutase, we engineered the K. marxianus L3 strain with the multicopy plasmid YG-KmSOD1 harboring the KmSOD1 gene. The production of KmSOD1p in K. marxianus L3 and K. marxianus L3 (pYG-KmSOD1) in response to different compositions of the culture medium was evaluated. The highest specific activity (472 U(SOD) mg(prot) (-1)) and the highest volumetric yield (8.8 x 10(5) U(SOD) l(-1)) were obtained by the recombinant strain overexpressing KmSOD1 in the presence of Cu(2+) and Zn(2+) supplements to the culture media. The best performing culture conditions were positively applied to a laboratory scale fed-batch process reaching a volumetric yield of 1.4 x 10(6) U(SOD) l(-1).

KlPMR1 inactivation and calcium addition enhance secretion of non-hyperglycosylated heterologous proteins in Kluyveromyces lactis.

The Kluyveromyces lactis KlPMR1 gene is the functional homologue of Saccharomyces cerevisiae PMR1 which encodes a Ca(2+)-ATPase localized in the Golgi apparatus. We studied the effects of KlPMR1 inactivation on the glycosylation and secretion of native and heterologous proteins in K. lactis. We used acid phosphatase, recombinant human serum albumin and alpha-glucoamylase from Arxula adeninivorans as reporter proteins. The Klpmr1Delta strain showed enhanced secretion of the heterologous proteins analyzed; the improved rHSA production did not result from enhanced transcription but rather involved increased translation and/or secretion efficiency. The growth rate of mutant cells resulted slower as compared to that of wild-type strain. The addition of 10mM calcium to the culture medium, however, not only completely relieved the growth defect of the mutant cells but also improved the rate of heterologous proteins production. Moreover, the addition of this ion in the culture medium of K. lactis did not suppress the glycosylation defects; this is an important difference with respect to S. cerevisiae where the glycosylation is partially restored by Ca(2+) addition. The Klpmr1Delta strain as a host offers thus an additional advantage for those cases requiring that the produced recombinant protein would not result hyperglycosylated.

The UDPase activity of the Kluyveromyces lactis Golgi GDPase has a role in uridine nucleotide sugar transport into Golgi vesicles.

In Saccharomyces cerevisiae a Golgi lumenal GDPase (ScGda1p) generates GMP, the antiporter required for entry of GDP-mannose, from the cytosol, into the Golgi lumen. Scgda1 deletion strains have severe defects in N- and O-mannosylation of proteins and glycosphingolipids. ScGda1p has also significant UDPase activity even though S. cerevisiae does not utilize uridine nucleotide sugars in its Golgi lumen. Kluyveromyces lactis, a species closely related to S. cerevisiae, transports UDP-N-acetylglucosamine into its Golgi lumen, where it is the sugar donor for terminal N-acetylglucosamine of the mannan chains. We have identified and cloned a K. lactis orthologue of ScGda1p. KlGda1p is 65% identical to ScGda1p and shares four apyrase conserved regions with other nucleoside diphosphatases. KlGda1p has UDPase activity as ScGda1p. Transport of both GDP-mannose, and UDP-GlcNAc was decreased into Golgi vesicles from Klgda1 null mutants, demonstrating that KlGda1p generates both GMP and UMP required as antiporters for guanosine and uridine nucleotide sugar transport into the Golgi lumen. Membranes from Klgda1 null mutants showed inhibition of glycosyltransferases utilizing uridine- and guanosine-nucleotide sugars, presumably due to accumulation of nucleoside diphosphates because the inhibition could be relieved by addition of apyrase to the incubations. KlGDA1 and ScGDA1 restore the wild-type phenotype of the other yeast gda1 deletion mutant. Surprisingly, KlGDA1 has only a role in O-glycosylation in K. lactis but also complements N-glycosylation defects in S. cerevisiae. Deletion mutants of both genes have altered cell wall stability and composition, demonstrating a broader role for the above enzymes.

vga Mutants of Kluyveromyces lactis show cell integrity defects.

We studied the cell wall alterations that occur in mutants of Kluyveromyces lactis impaired in glycosylation. The mutants belong to four complementation groups named vga1 to vga4 (vanadate glycosylation affected), characterized by sodium orthovanadate resistance and alteration of the glycosylation profile of native invertase. A drastic reduction of the alkali-soluble fraction of the beta-D-glucan was observed in vga1, vga2 and vga3 cells, accompanied by an increase in the chitin content of the cell wall. In vga4 cells, both beta-D-glucan fractions (alkali-soluble and alkali-insoluble) were reduced to about half of the corresponding wild-type value but the chitin content was normal. A protein related to Fks1p, the catalytic subunit of the major 1,3-beta-D-glucan synthase of S. cerevisiae, was detected in K. lactis. The amount of this Fks1p-like protein increased 7-10 times in vga1, vga2 and vga3 mutants as compared to wild-type cells; the same strains released significant amounts of beta-D-glucan in the culture supernatant. These mutations also resulted in abnormally thick cell walls with conspicuous irregularities in the structure, as revealed by electron microscopy and by an altered resistance to Zymolyase. The observed high responsiveness of cell wall phenotypes to alterations of glycosylation make K. lactis an attractive system for studying the interconnections between these processes.

Disruption of six novel genes from chromosome VII of Saccharomyces cerevisiae reveals one essential gene and one gene which affects the growth rate.

Six ORFs of unknown function located on chromosome VII of Saccharomyces cerevisiae were disrupted in two different genetic backgrounds, and the phenotype of the generated mutants was analysed. Disruptions of ORFs YGR256w, YGR272c, YGR273c, YGR275w and YGR276c were carried out using the disruption marker kanMX4 flanked by short homology regions, whereas ORF YGR255c was inactivated with a long flanking homology (LFH) disruption cassette (Wach et al., 1994). Tetrad analysis of the heterozygous disruptants revealed that ORF YGR255c, previously identified as COQ6 and encoding a protein involved in the biosynthesis of coenzime Q (Tzagoloff and Dieckmann, 1990), is an essential gene. The same analysis also revealed that sporulation of the ygr272cDelta heterozygous diploid produced two small colonies per ascus that were also G418-resistant, indicating that the inactivation of ORF YGR272c could result in a slower growth rate. This result was confirmed by growth tests of the haploid disruptants and by complementation of the phenotype after transformation with a plasmid carrying the cognate gene. No phenotypes could be associated to the inactivation of ORFs YGR256w, YGR273c, YGR275w and YGR276c. Two of these genes have recently been further characterized: ORF YGR255w, renamed RTT102, encodes a regulator of the Ty1-element transposition, whereas ORF YGR276c was found to encode the 70 kDa RNase H activity and was renamed RNH70 (Frank et al., 1999).

How to bring orphan genes into functional families.

In the framework of the B1 Consortium of the EUROFAN-1 project, we set up a series of simple phenotypic tests that can be performed on a large number of strains at a time. This methodological approach was intended to help assign functions of putative genes coding for unknown proteins to several specific aspects of cell biology. The tests were chosen to study phenotypes which should be affected by numerous genes. In this report, we examined the sensitivity/resistance or the adaptation of the cell to physical or chemical stresses (thermotolerance, osmotolerance and ethanol sensitivity), the effects of the alteration of the level of protein phosphorylation (sensitivity or resistance to compounds affecting the activity of protein kinases or phosphatases) and the effects of compounds interfering with synthesis of nucleic acids or proteins. Deletions in 66 genes of unknown function have been tested in 21 different conditions. In many deletant strains, phenotypes were observed and, for the most promising candidates, tetrad analysis was performed in order to verify co-segregation of the deletion marker with the phenotype.

The KlPMR1 gene of Kluyveromyces lactis encodes for a P-type Ca(2+)-ATPase.

A novel P-type Ca(2+)-ATPase gene has been cloned and sequenced in the yeast Kluyveromyces lactis. The gene has been named KlPMR1 and is localized on chromosome I. The putative gene product contains 936 residues and has a calculated molecular weight of 102,437 Da. Analysis of deduced amino acid sequence (KlPmr1p) indicated that the encoded protein retains all the highly conserved domains characterizing the P-type ATPases. KlPmr1p shares 71% amino acid identity with Pmr1p of S. cerevisiae, 62% with HpPmr1p of Hansenula polymorpha, 56% with Y1Pmr1p of Yarrowia lipolytica and 52% with the Ca(2+)-ATPase encoded for by the SPCA1 gene of Rattus norvegicus; these similarities place KlPmr1p in the SPCA group (secretory pathway Ca(2+)-ATPase) of the P-type ATPases. The K. lactis strain harbouring the Klpmr1 disrupted gene is not able to grow in presence of low calcium concentrations and shows hypersensitivity to high concentrations of EGTA in the medium. These defects are relieved by PMR1 of S. cerevisiae on a centromeric plasmid, demonstrating that KlPMR1 encodes for a functional Pmr1p homologue.

Mutants of Kluyveromyces lactis with altered protein glycosylation are affected in cell wall morphogenesis.

We isolated spontaneous mutants resistant to sodium orthovanadate in the biotechnologically significant yeast Kluyveromyces lactis. Resistance behaved as a recessive character in all mutants analyzed. Four genes were defined by complementation analysis, from vga1 to vga4. These mutants showed defects in N-linked as well as O-linked glycosylation processes. In addition, the mutants exhibited sensitivity to the aminoglycoside hygromycin B and to calcofluor white, with the exception of vga4; this mutant grew in the presence of the antibiotic as well as the parental wild type and was resistant to calcofluor. The mutations were accompanied by alterations in the cell wall structure, as revealed by the delocalization of chitin, changes in cell shape and size and by the clumpy aspect of the cultures. The mutants isolated provide basic tools for molecular and cellular analysis of glycosylation processes in K. lactis.

Isolation and characterisation of a ropy Lactobacillus strain producing the exopolysaccharide kefiran.

A capsular-polysaccharide-producing strain, LM-17, was isolated from kefir grains and was identified as a slime-forming, rod-shaped Lactobacillus. According to 1H- and 13C-NMR spectral data, the exopolysaccharide produced by the isolated bacterial strain is identical to the glucogalactan extracted from kefir grains and therefore known as kefiran. The kefiran produced was characterised by means of viscosity, optical rotatory power, circular dichroism and IR spectral measurements. A batch procedure was set up for the culture and extraction of the exopolysaccharide in laboratory conditions, resulting in a yield of 2 g/l purified kefiran from the culture supernatant of the LM-17 strain.