Evidence for a modulation of neutral trehalase activity by Ca2+ and cAMP signaling pathways in Saccharomyces cerevisiae

Protective role of trehalose in the Namib desert ant, Ocymyrmex robustior

Over recent decades, increasing attention has been paid to how low-molecular-weight molecules affect thermal tolerance in animals. Although the disaccharide sugar trehalose is known to serve as a thermal protectant in unicellular organisms, nothing is known about its potential role in insects. In this study, we investigated the effect of trehalose on heat tolerance in the Namib desert ant, Ocymyrmex robustior, one of the most thermotolerant animals found in terrestrial ecosystems. First, we tested whether a trehalose-supplemented diet increased worker survival following exposure to heat stress. Second, we assessed the degree of protein damage by comparing protein aggregation levels for trehalose-supplemented workers and control workers. Third, we compared the expression levels of three genes involved in trehalose metabolism. We found that trehalose supplementation significantly enhanced worker heat tolerance, increased metabolic levels of trehalose and reduced protein aggregation under conditions of heat stress. Expression levels of the three genes varied in a manner that was consistent with the maintenance of trehalose in the hemolymph and tissues under conditions of heat stress. Altogether, these results suggest that increased trehalose concentration may help protect Namib desert ant individuals against heat stress. More generally, they highlight the role played by sugar metabolites in boosting tolerance in extremophiles.

A protein kinase A-regulated network encodes short- and long-lived cellular memories

Cells can store memories of prior experiences to modulate their responses to subsequent stresses, as seen for the protein kinase A (PKA)-mediated general stress response in yeast, which is required for resistance against future stressful conditions. Using microfluidics and time-lapse microscopy, we quantitatively analyzed how the cellular memory of stress adaptation is encoded in single yeast cells. We found that cellular memory was biphasic. Short-lived memory was mediated by trehalose synthase and trehalose metabolism. Long-lived memory was mediated by PKA-regulated stress-responsive transcription factors and cytoplasmic messenger ribonucleoprotein granules. Short- and long-lived memory could be selectively induced by different priming input dynamics. Computational modeling revealed how the PKA-mediated regulatory network could encode previous stimuli into memories with distinct dynamics. This biphasic memory-encoding scheme might represent a general strategy to prepare for future challenges in rapidly changing environments.

The trehalose protective mechanism during thermal stress in Saccharomyces cerevisiae: the roles of Ath1 and Agt1

Trehalose on both sides of the bilayer is a requirement for full protection of membranes against stress. It was not known yet how trehalose, synthesized in the cytosol when dividing Saccharomyces cerevisiae cells are shifted from 28°C to 40°C, is transported to the outside and degraded when cells return to 28°C. According to our results, the lack of Agt1, a trehalose transporter, although had not affected trehalose synthesis, reduced cell tolerance to 51°C and increased lipid peroxidation. The damage was reversed when external trehalose was added during 40°C adaptation, confirming that the reason for the agt1Δ sensitivity is the absence of trehalose at the outside of the lipid bilayer. The 40-28°C condition caused cytosolic trehalase (Nth1) activation, reducing intracellular trehalose and, consequently, the survival rates after 51°C. Although lower than nth1Δ strain, cells deficient in acid trehalase (ath1Δ)  maintained increased trehalose levels after 40°C-28°C shift, which conferred protection against 51°C. Both Ath1 and Agt1 were found into vesicles near to plasma membrane in response to stress. This suggests that Agt1 containing vesicles would fuse with the membrane under 40°C to transport part of the cytosolic trehalose to the outside. By a similar mechanism, Ath1 would reach the cell surface to hydrolyze the external trehalose but only when the stress would be over. Corroborating this conclusion, Ath1 activity in soluble cell-free extracts increased after 40°C adaptation but decreased when cells returned to 28°C. During 40°C, Ath1 is confined into vesicles, avoiding the cleavage of the outside trehalose.

Decapping Scavenger (DcpS) enzyme: advances in its structure, activity and roles in the cap-dependent mRNA metabolism

Decapping Scavenger (DcpS) enzyme rids eukaryotic cells of short mRNA fragments containing the 5' mRNA cap structure, which appear in the 3'→5' mRNA decay pathway, following deadenylation and exosome-mediated turnover. The unique structural properties of the cap, which consists of 7-methylguanosine attached to the first transcribed nucleoside by a triphosphate chain (m(7)GpppN), guarantee its resistance to non-specific exonucleases. DcpS enzymes are dimers belonging to the Histidine Triad (HIT) superfamily of pyrophosphatases. The specific hydrolysis of m(7)GpppN by DcpS yields m(7)GMP and NDP. By precluding inhibition of other cap-binding proteins by short m(7)GpppN-containing mRNA fragments, DcpS plays an important role in the cap-dependent mRNA metabolism. Over the past decade, lots of new structural, biochemical and biophysical data on DcpS has accumulated. We attempt to integrate these results, referring to DcpS enzymes from different species. Such a synergistic characteristic of the DcpS structure and activity might be useful for better understanding of the DcpS catalytic mechanism, its regulatory role in gene expression, as well as for designing DcpS inhibitors of potential therapeutic application, e.g. in spinal muscular atrophy.

Gene identification and enzymatic properties of a membrane-bound trehalase from the ovary of Rhodnius prolixus

Trehalose represents the main hemolymph sugar in most insects and its metabolic availability is regulated by trehalase. In this study, trehalase activity associated with the reproductive system was investigated in the insect Rhodnius prolixus, a hematophagous hemipteran vector of Chagas' disease. A single-copy gene that encodes a membrane-bound trehalase (RpTre-2) was identified in the genome of R. prolixus. RpTre-2 deduced amino acid sequence is closely related to other insect membrane-bound trehalases. The expression of this gene was detected in all analyzed organs, including ovary, where total trehalase enzymatic activity was determined, and was highest at day 7 after blood meal. Ovary membranes showed a major trehalase specific activity, which confirmed the presence of a membrane-bound trehalase in this insect. This trehalase activity seemed not to be regulated at transcriptional level, as the expression of RpTre-2 gene in the ovary did not change over the days after feeding. Similarly, ovarian follicles at different developmental stages did not show any variation in the transcription level of this gene. The RpTre-2 kinetic parameters were also investigated. Activity was highest at pH 5.5 and followed Michaelis-Menten kinetics, with an apparent K(m) = 1.42 ± 0.36 mM and Vmax = 167.90 ± 12.91 nmol/mg protein/h. These data reveal the presence of a membrane-bound trehalase in R. prolixus that is active in ovary and probably takes part in the insect carbohydrate metabolism associated with the reproductive process.

In vivo phosphorylation of Ser21 and Ser83 during nutrient-induced activation of the yeast protein kinase A (PKA) target trehalase

The readdition of an essential nutrient to starved, fermenting cells of the yeast Saccharomyces cerevisiae triggers rapid activation of the protein kinase A (PKA) pathway. Trehalase is activated 5–10-fold within minutes and has been used as a convenient reporter for rapid activation of PKA in vivo. Although trehalase can be phosphorylated and activated by PKA in vitro, demonstration of phosphorylation during nutrient activation in vivo has been lacking. We now show, using phosphospecific antibodies, that glucose and nitrogen activation of trehalase in vivo is associated with phosphorylation of Ser²¹ and Ser⁸³. Unexpectedly, mutants with reduced PKA activity show constitutive phosphorylation despite reduced trehalase activation. The same phenotype was observed upon deletion of the catalytic subunits of yeast protein phosphatase 2A, suggesting that lower PKA activity causes reduced trehalase dephosphorylation. Hence, phosphorylation of trehalase in vivo is not sufficient for activation. Deletion of the inhibitor Dcs1 causes constitutive trehalase activation and phosphorylation. It also enhances binding of trehalase to the 14-3-3 proteins Bmh1 and Bmh2, suggesting that Dcs1 inhibits by preventing 14-3-3 binding. Deletion of Bmh1 and Bmh2 eliminates both trehalase activation and phosphorylation. Our results reveal that trehalase activation in vivo is associated with phosphorylation of typical PKA sites and thus establish the enzyme as a reliable read-out for nutrient activation of PKA in vivo.

Enzymatic control of anhydrobiosis-related accumulation of trehalose in the sleeping chironomid, Polypedilum vanderplanki

Larvae of an anhydrobiotic insect, Polypedilum vanderplanki, accumulate very large amounts of trehalose as a compatible solute on desiccation, but the molecular mechanisms underlying this accumulation are unclear. We therefore isolated the genes coding for trehalose metabolism enzymes, i.e. trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) for the synthesis step, and trehalase (TREH) for the degradation step. Although computational prediction indicated that the alternative splicing variants (PvTpsα/β) obtained encoded probable functional motifs consisting of a typical consensus domain of TPS and a conserved sequence of TPP, PvTpsα did not exert activity as TPP, but only as TPS. Instead, a distinct gene (PvTpp) obtained expressed TPP activity. Previous reports have suggested that insect TPS is, exceptionally, a bifunctional enzyme governing both TPS and TPP. In this article, we propose that TPS and TPP activities in insects can be attributed to discrete genes. The translated product of the TREH ortholog (PvTreh) certainly degraded trehalose to glucose. Trehalose was synthesized abundantly, consistent with increased activities of TPS and TPP and suppressed TREH activity. These results show that trehalose accumulation observed during anhydrobiosis induction in desiccating larvae can be attributed to the activation of the trehalose synthetic pathway and to the depression of trehalose hydrolysis.

Trehalose metabolism is important for heat stress tolerance and spore germination of Botrytis cinerea

To analyse the role of trehalose as stress protectant and carbon storage compound in the grey mould fungus Botrytis cinerea, mutants defective in trehalose-6-phosphate synthase (TPS1) and neutral trehalase (TRE1) were constructed. The Deltatps1 mutant was unable to synthesize trehalose, whereas the Deltatre1 mutant showed elevated trehalose levels compared to the wild-type and was unable to mobilize trehalose during conidial germination. Both mutants showed normal vegetative growth and were not affected in plant pathogenicity. Growth of the Deltatps1 mutant was more heat sensitive compared to the wild-type. Similarly, Deltatps1 conidia showed a shorter survival under heat stress, and their viability at moderate temperatures was strongly reduced. In germinating wild-type conidia, rapid trehalose degradation occurred only when germination was induced in the presence of nutrients. In contrast, little trehalose breakdown was observed during germination on hydrophobic surfaces in water. Here, addition of cAMP to conidia induced trehalose mobilization and accelerated the germination process, probably by activation of TRE1. In accordance with these data, both mutants showed germination defects only in the presence of sugars but not on hydrophobic surfaces in the absence of nutrients. The data indicate that in B. cinerea trehalose serves as a stress protectant, and also as a significant but not essential carbon source for germination when external nutrients are low. In addition, evidence was obtained that trehalose 6-phosphate plays a role as a regulator of glycolysis during germination.

Role of a novel dual flavin reductase (NR1) and an associated histidine triad protein (DCS-1) in menadione-induced cytotoxicity

Microsomal cytochrome P450 reductase catalyzes the one-electron transfer from NADPH via FAD and FMN to various electron acceptors, such as cytochrome P450s or to some anti-cancer quinone drugs. This results in generation of free radicals and toxic oxygen metabolites, which can contribute to the cytotoxicity of these compounds. Recently, a cytosolic NADPH-dependent flavin reductase, NR1, has been described which is highly homologous to the microsomal cytochrome P450 reductase. In this study, we show that over-expression of NR1 in human embryonic kidney cells enhances the cytotoxic action of the model quinone, menadione. Furthermore, we show that a novel human histidine triad protein DCS-1, which is expressed together with NR1 in many tissues, can significantly reduce menadione-induced cytotoxicity in these cells. We also show that DCS-1 binds NF1 and directly modulates its activity. These results suggest that NR1 may play a role in carcinogenicity and cell death associated with one-electron reductions.

Inferring protein-protein interactions through high-throughput interaction data from diverse organisms

MOTIVATION

Identifying protein-protein interactions is critical for understanding cellular processes. Because protein domains represent binding modules and are responsible for the interactions between proteins, computational approaches have been proposed to predict protein interactions at the domain level. The fact that protein domains are likely evolutionarily conserved allows us to pool information from data across multiple organisms for the inference of domain-domain and protein-protein interaction probabilities.

RESULTS

We use a likelihood approach to estimating domain-domain interaction probabilities by integrating large-scale protein interaction data from three organisms, Saccharomyces cerevisiae, Caenorhabditis elegans and Drosophila melanogaster. The estimated domain-domain interaction probabilities are then used to predict protein-protein interactions in S.cerevisiae. Based on a thorough comparison of sensitivity and specificity, Gene Ontology term enrichment and gene expression profiles, we have demonstrated that it may be far more informative to predict protein-protein interactions from diverse organisms than from a single organism.

AVAILABILITY

The program for computing the protein-protein interaction probabilities and supplementary material are available at http://bioinformatics.med.yale.edu/interaction.

A role for calcium in the regulation of neutral trehalase activity in the fission yeast Schizosaccharomyces pombe

Neutral trehalases mobilize trehalose accumulated by fungal cells as a protective and storage carbohydrate. A structural feature of these enzymes is the presence of an EF-like motif similar to that shown by many Ca2+-binding proteins. In this study we provide direct evidence for physical binding of Ca2+ to neutral trehalase (Ntp1p) of the fission yeast Schizosaccharomyces pombe, and show that aspartic residues at positions 97 and 108 in the conserved putative Ca2+-binding motif of Ntp1p appear to be responsible for this interaction. Mutations in these residues do not interfere with the ability of Ntp1p to associate in vivo with trehalose-6-phosphate synthase, but prevent activation of neutral trehalase triggered by the addition of glucose or by subjecting cells to stressing conditions. Strains expressing Ntp1p variants that are unable to bind Ca2+ partially resemble those devoid of the ntp1+ gene in terms of trehalose hyperaccumulation. Gel filtration of cell extracts from wild-type cells after EDTA treatment or from cells containing Ntp1p with mutations in aspartic acid residues within the Ca2+-binding site revealed that Ntp1p eluted mainly in an inactive conformation instead of the dimeric or trimeric active form of the enzyme. These results suggest that activation of S. pombe Ntp1p under different conditions depends upon Ca2+ binding through the Ca2+-binding motif as a prerequisite for correct enzyme oligomerization to its active form. Given the high degree of conservation of the Ca2+ accommodation site, this might be a general mechanism regulating neutral trehalase activity in other yeasts and filamentous fungi.

In silico and in vivo analysis reveal a novel gene in Saccharomyces cerevisiae trehalose metabolism

Background

The ability to respond rapidly to fluctuations in environmental changes is decisive for cell survival. Under these conditions trehalose has an essential protective function and its concentration increases in response to enhanced expression of trehalose synthase genes, TPS1, TPS2, TPS3 and TSL1. Intriguingly, the NTH1 gene, which encodes neutral trehalase, is highly expressed at the same time. We have previously shown that trehalase remains in its inactive non-phosphorylated form by the action of an endogenous inhibitor. Recently, a comprehensive two-hybrid analysis revealed a 41-kDa protein encoded by the YLR270w ORF, which interacts with NTH1p.

Results

In this work we investigate the correlation of this Trehalase Associated Protein, in trehalase activity regulation. The neutral trehalase activity in the ylr270w mutant strain was about 4-fold higher than in the control strain. After in vitro activation by PKA the ylr270w mutant total trehalase activity increased 3-fold when compared to a control strain. The expression of the NTH1 gene promoter fused to the heterologous reporter lacZ gene was evaluated. The mutant strain lacking YLR270w exhibited a 2-fold increase in the NTH1-lacZ basal expression when compared to the wild type strain.

Conclusions

These results strongly indicate a central role for Ylr270p in inhibiting trehalase activity, as well as in the regulation of its expression preventing a wasteful futile cycle of synthesis-degradation of trehalose.

Shared control of maltose and trehalose utilization in Candida utilis

Trehalose biosynthesis and its hydrolysis have been extensively studied in yeast, but few reports have addressed the catabolism of exogenously supplied trehalose. Here we report the catabolism of exogenous trehalose by Candida utilis. In contrast to the biphasic growth in glucose, the growth of C. utilis in a mineral medium with trehalose as the sole carbon and energy source is aerobic and exhibits the Kluyver effect. Trehalose is transported into the cell by an inducible trehalose transporter (K M of 8 mM and V MAX of 1.8 mol trehalose min-1 mg cell (dry weight)-1. The activity of the trehalose transporter is high in cells growing in media containing trehalose or maltose and very low or absent during the growth in glucose or glycerol. Similarly, total trehalase activity was increased from about 1.0 mU/mg protein in cells growing in glucose to 39.0 and 56.2 mU/mg protein in cells growing in maltose and trehalose, respectively. Acidic and neutral trehalase activities increased during the growth in trehalose, with neutral trehalase contributing to about 70% of the total activity. In addition to the increased activities of the trehalose transporter and trehalases, growth in trehalose promoted the increase in the activity of alpha-glucosidase and the maltose transporter. These results clearly indicate that maltose and trehalose promote the increase of the enzymatic activities necessary to their catabolism but are also able to stimulate each other's catabolism, as reported to occur in Escherichia coli. We show here for the first time that trehalose induces the catabolism of maltose in yeast.

A nuclear protein in Schizosaccharomyces pombe with homology to the human tumour suppressor Fhit has decapping activity

A number of eukaryotic proteins are already known to orchestrate key steps of mRNA metabolism and translation via interactions with the 5' m7GpppN cap. We have characterized a new type of histidine triad (HIT) motif protein (Nhm1) that co-purifies with the cap-binding complex eIF4F of Schizosaccharomyces pombe. Nhm1 is an RNA-binding protein that binds to m7GTP-Sepharose, albeit with lower specificity and affinity for methylated GTP than is typical for the cap-binding protein known as eukaryotic initiation factor 4E. Sequence searches have revealed that proteins with strong sequence similarity over all regions of the new protein exist in a wide range of eukaryotes, yet none has been characterized up to now. However, other proteins that share specific motifs with Nhm1 include the human Fhit tumour suppressor protein and the diadenosine 5', 5"'-P1, P4-tetraphosphate asymmetrical hydrolase of S. pombe. Our experimental work also reveals that Nhm1 inhibits translation in a cell-free extract prepared from S. pombe, and that it is therefore a putative translational modulator. On the other hand, purified Nhm1 manifests mRNA decapping activity, yet is physically distinct from the Saccharomyces cerevisiae decapping enzyme Dcp1. Moreover, fluorescence and immunofluorescence microscopy show that Nhm1 is predominantly, although not exclusively, nuclear. We conclude that Nhm1 has evolved as a special branch of the HIT motif superfamily that has the potential to influence both the metabolism and the translation of mRNA, and that its presence in S. pombe suggests the utilization of a novel decapping pathway.