The glyoxylate shunt protein ICL-1 protects from mitochondrial superoxide stress through activation of the mitochondrial unfolded protein response

Disrupting mitochondrial superoxide dismutase (SOD) causes neonatal lethality in mice and death of flies within 24 h after eclosion. Deletion of mitochondrial sod genes in C. elegans impairs fertility as well, but surprisingly is not detrimental to survival of progeny generated. The comparison of metabolic pathways among mouse, flies and nematodes reveals that mice and flies lack the glyoxylate shunt, a shortcut that bypasses part of the tricarboxylic acid (TCA) cycle. Here we show that ICL-1, the sole protein that catalyzes the glyoxylate shunt, is critical for protection against embryonic lethality resulting from elevated levels of mitochondrial superoxide. In exploring the mechanism by which ICL-1 protects against ROS-mediated embryonic lethality, we find that ICL-1 is required for the efficient activation of mitochondrial unfolded protein response (UPRmt) and that ATFS-1, a key UPRmt transcription factor and an activator of icl-1 gene expression, is essential to limit embryonic/neonatal lethality in animals lacking mitochondrial SOD. In sum, we identify a biochemical pathway that highlights a molecular strategy for combating toxic mitochondrial superoxide consequences in cells.

Ectopic expression of rice malate synthase in Arabidopsis revealed its roles in salt stress responses

Expression of rice malate synthase (OsMS), one of the two key genes in the glyoxylate cycle, is highly upregulated under salt stress. In this study, we aimed to investigate the role of OsMS in salt stress responses using the Arabidopsis T-DNA insertional mutant line of malate synthase (AtMS), an OsMS orthologous gene, for ectopic expression. Germination of the Atms mutant under salt stress was lower than that of Arabidopsis Col-0 wildtype (WT); furthermore, the two Atms mutant lines ectopically expressing OsMS reversed the salt-sensitive phenotype. Atms mutants salt-treated for 3 days exhibited higher electrolyte leakage, higher Na⁺/K⁺ ratio, lower expression of stress-responsive genes, and lower soluble sugar content than WT and the two OsMS-expressing Atms mutant lines. Consistently, Atms mutants salt-treated for 3 days followed by a 5-day recovery period displayed greater fresh-weight reduction. Notably, leaf greenness and chlorophyll and total carotenoid contents were higher in the Atms mutant lines than in the WT under stress. OsMS-expressing Atms mutants exhibited a change in pigment content closer to that of WT. During dark-induced senescence, an Atms mutant, Aticl, mutant (the other key gene in the glyoxylate cycle), and three double mutant lines of Atms and Aticl exhibited lower decreases in leaf greenness than the WT and OsMS-expressing Atms mutant lines. Furthermore, SAG12 expression levels in the Atms mutant, Aticl mutant, and three double mutant lines were lower than those in OsMS-expressing Atms mutant lines. Altogether, our data indicate that OsMS likely plays a key role in salt stress responses, possibly through the induction of leaf senescence.

Mechanistic assessment of tolerance to iron deficiency mediated by Trichoderma harzianum in soybean roots

AIMS

Iron (Fe) deficiency in soil is a continuing problem for soybean (Glycine max L.) production, partly as a result of continuing climate change. This study elucidates how Trichoderma harzianum strain T22 (TH) mitigates growth retardation associated with Fe-deficiency in a highly sensitive soybean cultivar.

METHODS AND RESULTS

Soil TH supplementation led to mycelial colonization and the presence of UAOX1 gene in roots that caused substantial improvement in chlorophyll score, photosynthetic efficiency and morphological parameters, indicating a positive influence on soybean health. Although rhizosphere acidification was found to be a common feature of Fe-deficient soybean, the upregulation of Fe-reductase activity (GmFRO2) and total phenol secretion were two of the mechanisms that substantially increased the Fe availability by TH. Heat-killed TH applied to soil caused no improvement in photosynthetic attributes and Fe-reductase activity, confirming the active role of TH in mitigating Fe-deficiency. Consistent increases in tissue Fe content and increased Fe-transporter (GmIRT1, GmNRAMP2a, GmNRAMP2b and GmNRAMP7) mRNA levels in roots following TH supplementation were observed only under Fe-deprivation. Root cell death, electrolyte leakage, superoxide (O2 •- ) and hydrogen peroxide (H2 O2 ) substantially declined due to TH in Fe-deprived plants. Further, the elevation of citrate and malate concentration along with the expression of citrate synthase (GmCs) and malate synthase (GmMs) caused by TH suggest improved chelation of Fe in Fe-deficient plants. Results also suggest that TH has a role in triggering antioxidant defence by increasing the activity of glutathione reductase (GR) along with elevated S-metabolites (glutathione and methionine) to stabilize redox status under Fe-deficiency.

CONCLUSIONS

TH increases the availability and mobilization of Fe by inducing Fe-uptake pathways, which appears to help provide resistance to oxidative stress associated with Fe-shortage in soybean.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings indicate that while Fe deficiency does not affect the rate or degree of TH hyphal association in soybean roots, the beneficial effects of TH alone may be Fe deficiency-dependent.

Expression regulation of MALATE SYNTHASE involved in glyoxylate cycle during protocorm development in Phalaenopsis aphrodite (Orchidaceae)

Orchid (Orchidaceae) is one of the largest families in angiosperms and presents exceptional diversity in lifestyle. Their unique reproductive characteristics of orchid are attracted by scientist for centuries. One of the synapomorphies of orchid plants is that their seeds do not contain endosperm. Lipids are used as major energy storage in orchid seeds. However, regulation and mobilization of lipid usage during early seedling (protocorm) stage of orchid is not understood. In this study, we compared transcriptomes from developing Phalaenopsis aphrodite protocorms grown on 1/2-strength MS medium with sucrose. The expression of P. aphrodite MALATE SYNTHASE (PaMLS), involved in the glyoxylate cycle, was significantly decreased from 4 days after incubation (DAI) to 7 DAI. On real-time RT-PCR, both P. aphrodite ISOCITRATE LYASE (PaICL) and PaMLS were down-regulated during protocorm development and suppressed by sucrose treatment. In addition, several genes encoding transcription factors regulating PaMLS expression were identified. A gene encoding homeobox transcription factor (named PaHB5) was involved in positive regulation of PaMLS. This study showed that sucrose regulates the glyoxylate cycle during orchid protocorm development in asymbiotic germination and provides new insights into the transcription factors involved in the regulation of malate synthase expression.

Optimized NMR Experiments for the Isolation of I=1/2 Manifold Transitions in Methyl Groups of Proteins

Optimized NMR experiments are developed for isolating magnetization belonging to the I=1/2 manifolds of 13 CH3 methyl groups in proteins, enabling the manipulation of the magnetization of a 13 CH3 moiety as if it were an AX (1 H-13 C) spin-system. These experiments result in the same 'simplification' of a 13 CH3 spin-system that would be obtained from the production of {13 CHD2 }-methyl-labeled protein samples. The sensitivity of I=1/2 manifold-selection experiments is a factor of approximately 2 less than that of the corresponding experiments acquired on {13 CHD2 }-labeled methyl groups. The methodology described here is primarily intended for small-to-medium sized proteins, where the losses in sensitivity associated with the isolation of I=1/2 manifold transitions can be tolerated. Several NMR applications that benefit from simplification of the 13 CH3 (AX3 ) spin-systems are described, with an emphasis on the measurements of methyl 1 H-13 C residual dipolar couplings in a {13 CH3 }-methyl-labeled deletion mutant of the human chaperone DNAJB6b, where modulation of NMR signal intensities due to evolution of methyl 1 H-13 C scalar and dipolar couplings follows a simple cosine function characteristic of an AX (1 H-13 C) spin-system, significantly simplifying data analysis.

Is Autophagy Involved in Pepper Fruit Ripening?

Autophagy is a universal self-degradation process involved in the removal and recycling of cellular constituents and organelles; however, little is known about its possible role in fruit ripening, in which the oxidation of lipids and proteins and changes in the metabolism of different cellular organelles occur. In this work, we analyzed several markers of autophagy in two critical maturation stages of pepper (Capsicum annuum L.) fruits where variations due to ripening become clearly visible. Using two commercial varieties that ripen to yellow and red fruits respectively, we studied changes in the gene expression and protein content of several autophagy (ATG) components, ATG4 activity, as well as the autophagy receptor NBR1 and the proteases LON1 and LON2. Additionally, the presence of intravacuolar vesicles was analyzed by electron microscopy. Altogether, our data reveal that autophagy plays a role in the metabolic changes which occur during ripening in the two studied varieties, suggesting that this process may be critical to acquiring final optimal quality of pepper fruits.

Overproduction of recombinant E. coli malate synthase enhances Chlamydomonas reinhardtii biomass by upregulating heterotrophic metabolism

High uptake of malate and efficient distribution of intracellular malate to organelles contributed to biomass increase, reducing maintenance energy. In this study, transgenic Chlamydomonas reinhardtii was developed that stably expresses malate synthase in the chloroplast. The strains under glyoxylate treatment showed 19% more increase in microalgal biomass than wild-type. By RNA analysis, transcript levels of malate dehydrogenase (MDH4) and acetyl-CoA synthetase (ACS3), isocitrate lyase (ICL1) and malate synthase (MAS1), were significantly more expressed (17%, 42%, 24%, and 18% respectively), which was consistent with reported heterotrophic metabolism flux analysis with the objective function maximizing biomass. Photosynthetic F_v/F_m was slightly reduced. A more meticulous analysis is necessary, but, in the transgenic microalgae with malate synthase overexpression, the metabolism is likely to more rely on heterotrophic energy production via TCA cycle and glyoxylate shunt than on photosynthesis, resulting in the increase in microalgal biomass.

Structural investigation of a chaperonin in action reveals how nucleotide binding regulates the functional cycle

Chaperonins are ubiquitous protein assemblies present in bacteria, eukaryota, and archaea, facilitating the folding of proteins, preventing protein aggregation, and thus participating in maintaining protein homeostasis in the cell. During their functional cycle, they bind unfolded client proteins inside their double ring structure and promote protein folding by closing the ring chamber in an adenosine 5'-triphosphate (ATP)-dependent manner. Although the static structures of fully open and closed forms of chaperonins were solved by x-ray crystallography or electron microscopy, elucidating the mechanisms of such ATP-driven molecular events requires studying the proteins at the structural level under working conditions. We introduce an approach that combines site-specific nuclear magnetic resonance observation of very large proteins, enabled by advanced isotope labeling methods, with an in situ ATP regeneration system. Using this method, we provide functional insight into the 1-MDa large hsp60 chaperonin while processing client proteins and reveal how nucleotide binding, hydrolysis, and release control switching between closed and open states. While the open conformation stabilizes the unfolded state of client proteins, the internalization of the client protein inside the chaperonin cavity speeds up its functional cycle. This approach opens new perspectives to study structures and mechanisms of various ATP-driven biological machineries in the heat of action.

Down-regulation of malate synthase in Mycobacterium tuberculosis H37Ra leads to reduced stress tolerance, persistence and survival in macrophages

Malate synthase is a condensing enzyme responsible for conversion of glyoxylate to malate in the presence of acetyl-CoA. This reaction helps in bypassing the TCA cycle reactions involving carbon loss and leads to diverting some of the carbon skeletons to gluconeogenic events while rest can continue to provide TCA cycle intermediates. Malate synthase (GlcB) is encoded by MRA_1848 of Mycobacterium tuberculosis H37Ra (Mtb-Ra). We developed a knockdown (KD) Mtb-Ra strain by down-regulating GlcB. The survival studies suggested increased susceptibility to oxidative and nitrosative stress as well as to rifampicin. The susceptibility profile was reversed in the presence of free radical scavengers. Also, KD showed reduced biofilm maturation, failed to enter persistent state, and showed reduced growth inside macrophages. The study of post-endocytosis events showed differences in late stage endosomal maturation behavior in macrophages infected with KD compared to WT. Increased iNOS, LAMP1 and cathepsin D expression was observed in macrophages infected with KD compared to WT.

Metabolic Engineering of Photorespiration

The introduction of two alternative glycolate catabolic pathways in the chloroplasts of Arabidopsis thaliana rendered plants with increased biomass. To introduce these synthetic pathways, the selected genes were stepwise integrated in the nuclear genome of wild-type plants. These plants were transformed by Agrobacterium tumefaciens carrying the binary vectors using the floral dip method. Selection of transformants was conducted using different selection agents and the expression of the transgenes was confirmed by PCR and enzyme activity measurements.

The Mycobacterium tuberculosis H37Ra gene MRA_1916 causes growth defects upon down-regulation

D-amino acid oxidases play an important role in converting D-amino acids to their corresponding α-keto acids. MRA_1916 of Mycobacterium tuberculosis H37Ra (Mtb-Ra) is annotated to be a D-amino acid oxidase (DAO). However, not much information is available about its physiological role during Mtb-Ra growth and survival. The present study was taken-up to understand the role of DAO during different stages of growth and effect of its down-regulation on growth. Recombinant Mtb-Ra strains with DAO and GlcB (malate synthase: MRA_1848) gene knockdown were developed and their growth was studied using Microtiter Alamar Blue Assay (MABA) with glycerol, acetate and glycine as a carbon source. Ethyl bromopyruvate (BrP) was used as an inhibitor of GlcB. MABA study showed inhibition of wild-type (WT) and knockdowns in the presence of BrP (2.5mM). However, growth inhibition of WT was less noticeable at lower concentrations of BrP. Mtb-Ra with DAO knockdown showed poor utilization of glycine in the presence of BrP. The DAO localization study showed its prominent distribution in cytosolic fraction and to some extent in cell wall and membrane fractions. Growth profile of WT under oxygen and nutritional stress showed changes in expression of DAO, GlcB, PckA (phosphoenolpyruvate carboxykinase: MRA_0219) and GlyA1 (serine hydroxymethyltransferase: MRA_1104).

β-Carboline alkaloids from Galianthe ramosa inhibit malate synthase from Paracoccidioides spp

As part of our continuing chemical and biological analyses of Rubiaceae species from Cerrado, we isolated novel alkaloids 1 and 2, along with known compounds epicatechin, ursolic acid, and oleanolic acid, from Galianthe ramosa. Alkaloid 2 inhibited malate synthase from the pathogenic fungus Paracoccidioides spp. This enzyme is considered an important molecular target because it is not found in humans. Molecular docking simulations were used to describe the interactions between the alkaloids and malate synthase.

Ectopic expression of CaRLK1 enhances hypoxia tolerance with increasing alanine production in Nicotiana spp

In a previous report, the pepper receptor-like kinase 1 (CaRLK1) gene was shown to be responsible for negatively regulating plant cell death caused by pathogens via accumulation of superoxide anions. Here, we examined whether this gene also plays a role in regulating cell death under abiotic stress. The total concentrations of free amino acids in CaRLK1-overexpressed cells (RLKox) increased by twofold compared with those of the wild-type Nicotiana tabacum BY-2 cells. Additionally, alanine and pyruvate concentrations increased by approximately threefold. These accumulations were associated with both the expression levels of the isocitrate lyase (ICL) and malate synthase genes and their specific activities, which were preferentially up-regulated in the RLKox cells. The expression levels of ethylene biosynthetic genes (ACC synthase and ACC oxidase) were suppressed, but those of both the metallothionein and lesion simulating disease 1 genes increased in the RLKox cells during submergence-induced hypoxia. The specific activity of catalase, which is involved in protecting ICL from reactive oxygen species, was also induced threefold in the RLKox cells. The primary roots of the transgenic plants that were exposed to hypoxic conditions grew at similar rates to those in normal conditions. We propose that CaRLK1 maintains a persistent hypoxia-resistant phenotype.

Metabolic engineering of Bacillus subtilis for growth on overflow metabolites

BACKGROUND

The genome of the important industrial host Bacillus subtilis does not encode the glyoxylate shunt, which is necessary to utilize overflow metabolites, like acetate or acetoin, as carbon source. In this study, the operon encoding the isocitrate lyase (aceB) and malate synthase (aceA) from Bacillus licheniformis was transferred into the chromosome of B. subtilis. The resulting strain was examined in respect to growth characteristics and qualities as an expression host.

RESULTS

Our results show that the modified B. subtilis strain is able to grow on the C2 compound acetate. A combined transcript, protein and metabolite analysis indicated a functional expression of the native glyoxylate shunt of B. lichenifomis in B. subtilis. This metabolically engineered strain revealed better growth behavior and an improved activity of an acetoin-controlled expression system.

CONCLUSIONS

The glyoxylate shunt of B. licheniformis can be functionally transferred to B. subtilis. This novel strain offers improved properties for industrial applications, such as growth on additional carbon sources and a greater robustness towards excess glucose feeding.

Metabolic acclimation to excess light intensity in Chlamydomonas reinhardtii

There are several well-described acclimation responses to excess light in green algae but the effect on metabolism has not been thoroughly investigated. This study examines the metabolic changes during photoacclimation to high-light (HL) stress in Chlamydomonas reinhardtii using nuclear magnetic resonance and mass spectrometry. Using principal component analysis, a clear metabolic response to HL intensity was observed on global metabolite pools, with major changes in the levels of amino acids and related nitrogen metabolites. Amino acid pools increased during short-term photoacclimation, but were especially prominent in HL-acclimated cultures. Unexpectedly, we observed an increase in mitochondrial metabolism through downstream photorespiratory pathways. The expression of two genes encoding key enzymes in the photorespiratory pathway, glycolate dehydrogenase and malate synthase, were highly responsive to the HL stress. We propose that this pathway contributes to metabolite pools involved in nitrogen assimilation and may play a direct role in photoacclimation. Our results suggest that primary and secondary metabolism is highly pliable and plays a critical role in coping with the energetic imbalance during HL exposure and a necessary adjustment to support an increased growth rate that is an effective energy sink for the excess reducing power generated during HL stress.

Non-traditional antibacterial screening approaches for the identification of novel inhibitors of the glyoxylate shunt in gram-negative pathogens

Antibacterial compounds that affect bacterial viability have traditionally been identified, confirmed, and characterized in standard laboratory media. The historical success of identifying new antibiotics via this route has justifiably established a traditional means of screening for new antimicrobials. The emergence of multi-drug-resistant (MDR) bacterial pathogens has expedited the need for new antibiotics, though many in the industry have questioned the source(s) of these new compounds. As many pharmaceutical companies' chemical libraries have been exhaustively screened via the traditional route, we have concluded that all compounds with any antibacterial potential have been identified. While new compound libraries and platforms are being pursued, it also seems prudent to screen the libraries we currently have in hand using alternative screening approaches. One strategy involves screening under conditions that better reflect the environment pathogens experience during an infection, and identifying in vivo essential targets and pathways that are dispensable for growth in standard laboratory media in vitro. Here we describe a novel screening strategy for identifying compounds that inhibit the glyoxylate shunt in Pseudomonas aeruginosa, a pathway that is required for bacterial survival in the pulmonary environment. We demonstrate that these compounds, which were not previously identified using traditional screening approaches, have broad-spectrum antibacterial activity when they are tested under in vivo-relevant conditions. We also show that these compounds have potent activity on both enzymes that comprise the glyoxylate shunt, a feature that was supported by computational homology modeling. By dual-targeting both enzymes in this pathway, we would expect to see a reduced propensity for resistance development to these compounds. Taken together, these data suggest that understanding the in vivo environment that bacterial pathogens must tolerate, and adjusting the antibacterial screening paradigm to reflect those conditions, could identify novel antibiotics for the treatment of serious MDR pathogens.

Detection of Mycobacterium tuberculosis GlcB or HspX Antigens or devR DNA impacts the rapid diagnosis of tuberculous meningitis in children

Background

Tuberculous meningitis (TBM) is the most common form of neurotuberculosis and the fifth most common form of extrapulmonary TB. Early diagnosis and prompt treatment are the cornerstones of effective disease management. The accurate diagnosis of TBM poses a challenge due to an extensive differential diagnosis, low bacterial load and paucity of cerebrospinal fluid (CSF) especially in children.

Methodology/Principal Findings

We describe the utility of ELISA and qPCR for the detection of Mycobacterium tuberculosis (M. tb) proteins (GlcB, HspX, MPT51, Ag85B and PstS1) and DNA for the rapid diagnosis of TBM. CSF filtrates (n = 532) derived from children were classified as ‘Definite’ TBM (M. tb culture positive, n = 29), ‘Probable and Possible’ TBM (n = 165) and ‘Not-TBM’ including other cases of meningitis or neurological disorders (n = 338). ROC curves were generated from ELISA and qPCR data of ‘Definite’ TBM and Non-Tuberculous infectious meningitis (NTIM) samples and cut-off values were derived to provide ≥95% specificity. devR qPCR, GlcB, HspX and PstS1 ELISAs showed 100% (88;100) sensitivity and 96–97% specificity in ‘Definite’ TBM samples. The application of these cut-offs to ‘Probable and Possible’ TBM groups yielded excellent sensitivity (98%, 94;99) and specificity (98%, 96;99) for qPCR and for GlcB, HspX and MPT51 antigen ELISAs (sensitivity 92–95% and specificity 93–96%). A test combination of qPCR with GlcB and HspX ELISAs accurately detected all TBM samples at a specificity of ∼90%. Logistic regression analysis indicated that these tests significantly added value to the currently used algorithms for TBM diagnosis.

Conclusions

The detection of M. tb GlcB/HspX antigens/devR DNA in CSF is likely to improve the utility of existing algorithms for TBM diagnosis and also hasten the speed of diagnosis.

Heterologous C-terminal signals effectively target fluorescent fusion proteins to leaf peroxisomes in diverse plant species

Peroxisomes are functionally diverse organelles that are wholly dependent on import of nuclear-encoded proteins. The signals that direct proteins into these organelles are either found at the C-terminus (type 1 peroxisomal targeting signal; PTS1) or N-terminus (type 2 peroxisomal targeting signal; PTS2) of the protein. Based on a limited number of tests in heterologous systems, PTS1 signals appear to be conserved across species. To further test the generality of this conclusion and to establish the extent to which the PTS1 signals can be relied on for biotechnological purposes across species, we tested two PTS1 signals for their ability to target fluorescent proteins in diverse plant species. Transient assays following microprojectile bombardment showed that the six amino acid PTS1 sequence (RAVARL) from spinach glycolate oxidase effectively targets green fluorescent fusion protein to the leaf peroxisomes in all 20 crops tested, including four monocots (sugarcane, wheat, corn and onion) and 16 dicots (carrot, cucumber, broccoli, tomato, lettuce, turnip, radish, cauliflower, cabbage, capsicum, celery, tobacco, petunia, beetroot, eggplant and coriander). Similarly, results indicated that the 10 amino acid PTS1 sequence (IHHPRELSRL) from pumpkin malate synthase effectively targets red fluorescent fusion protein to the leaf peroxisomes in all four crops tested including monocot (sugarcane) and dicot (cabbage, celery and pumpkin) species. These signal sequences should be useful metabolic engineering tools to direct recombinant proteins to the leaf peroxisomes in diverse plant species of biotechnological interest.

A functionally active dimer of mycobacterium tuberculosis malate synthase G

Malate synthase G is an important housekeeping enzyme of glyoxylate shunt in mycobacterium. The pleotropic function of this protein by virtue of its intracellular/extracellular localization and its behavior as an adhesin and virulence factor is quite enigmatic. Despite its importance in mycobacterium persistence, we do not know much about its biophysical and biochemical properties. Earlier reports suggest that the enzyme exists only as a monomer in prokaryotes; however, we observed the existence of both active monomer and dimer forms of the enzyme under physiological conditions. The dimeric form of the enzymes is more stable as compared to the monomeric form as evident from various biophysical parameters. In addition, the dimeric enzyme also shows enhanced stability against proteolysis than the monomers. Based on these studies, it seems that dimerization is an important factor in regulating stability. The differential localization and diverse functions of malate synthase other than its enzymatic role might be triggering the stabilization of the enzyme dimer and modulation of activity and stability in vivo.

The malate synthase of Paracoccidioides brasiliensis is a linked surface protein that behaves as an anchorless adhesin

BACKGROUND

The pathogenic fungus Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis (PCM). This is a pulmonary mycosis acquired by inhalation of fungal airborne propagules that can disseminate to several organs and tissues leading to a severe form of the disease. Adhesion and invasion to host cells are essential steps involved in the internalization and dissemination of pathogens. Inside the host, P. brasiliensis may use the glyoxylate cycle for intracellular survival.

RESULTS

Here, we provide evidence that the malate synthase of P. brasiliensis (PbMLS) is located on the fungal cell surface, and is secreted. PbMLS was overexpressed in Escherichia coli, and polyclonal antibody was obtained against this protein. By using Confocal Laser Scanning Microscopy, PbMLS was detected in the cytoplasm and in the cell wall of the mother, but mainly of budding cells of the P. brasiliensis yeast phase. PbMLSr and its respective polyclonal antibody produced against this protein inhibited the interaction of P. brasiliensis with in vitro cultured epithelial cells A549.

CONCLUSION

These observations indicated that cell wall-associated PbMLS could be mediating the binding of fungal cells to the host, thus contributing to the adhesion of fungus to host tissues and to the dissemination of infection, behaving as an anchorless adhesin.

Hydrogen peroxide induced oxidation of peroxisomal malate synthase and catalase

Peroxisomes contain oxidases that produce H(2)O(2), which can result in protein oxidation. To test the vulnerability of peroxisomal proteins to oxidation in vivo the organelles were isolated from castor bean endosperm incubated with H(2)O(2). When peroxisomes were exposed to H(2)O(2)in vivo, the peroxisomal proteins exhibited an increase in carbonylation as detected in avidin blots of biotin hydrazide derivatized samples. Biotin-tagged peptides from trypsin digests of the proteins were analyzed by mass spectroscopy and compared to the masses of peptides from the same protein that had not been biotin-tagged and from proteins not exposed to excess H(2)O(2). H(2)O(2) exposure was found to increase the activity of catalase (CAT), and to increase the number of oxidized peptides found in CAT and malate synthase (MS). CAT had 10 peptides that were affected by in vivo exposure to H(2)O(2) and MS had 8. These sites of oxidation have definable locations within the proteins' structures.

An efficient protocol for the complete incorporation of methyl-protonated alanine in perdeuterated protein

A strategy for the introduction of ((1)H,(13)C-methyl)-alanine into perdeuterated proteins is described. Specific protonation of alanine methyl groups to a level of 95% can be achieved by overexpressing proteins in M9/D(2)O based bacterial growth medium supplemented with 800 mg/l of 2-[(2)H], 3-[(13)C] L: -alanine. However, though simple, this approach results in undesired, non-specific background labeling due to isotope scrambling via different amino acid metabolic pathways. Following a careful analysis of known metabolic pathways we found that co-addition of perdeuterated forms of alpha-ketoisovalerate-d(7), succinate-d(4) and L: -isoleucine-d(10) with labeled L: -alanine, reduces undesired background labeling to <1%. When combined with recently developed methyl TROSY experiments, this methyl-specific labeling protocol permits the acquisition of excellent quality correlation spectra of alanine methyl groups in high molecular weight proteins. Our cost effective strategy offers a significant enhancement in the level of incorporation of methyl-labeled alanine in overexpressed proteins over previously reported methods.

The role of the glyoxylate cycle in the symbiotic fungus Tuber borchii: expression analysis and subcellular localization

Expression profiles of isocitrate lyase (TbICL), malate synthase (TbMLS) and fructose-1,6-bisphosphatase (TbFBP) from the mycorrhizal ascomycete Tuber borchii were investigated by real-time RT-PCR in fruiting bodies at different stages of maturation. In addition, a time course experiment was set up to determine how the transcription profile of TbICL, TbMLS and TbFBP in axenic-grown mycelia is affected by different carbon sources. The transcript levels of the three genes in the fruiting bodies were all much higher than those measured in the vegetative stage. The investigation on axenic-grown mycelia revealed that the main positive regulator of TbICL and TbMLS gene expression is the availability of acetate and ethanol, while oleic acid is a too complex substrate for the limited degradative capacities of T. borchii. Immunolabelling on axenic-grown mycelia showed a co-localization of TbICL and the peroxisomal marker protein FOX2. This result demonstrated that in T. borchii ICL is compartmentalized in peroxisomes. The high induction of TbICL, TbMLS and TbFBP transcription and the translocation of lipids in fruiting bodies let us hypothesize that glyoxylate cycle and gluconeogenesis are key metabolic pathways in the recycling of existing cell material and the channelling towards the biosynthesis of new cell components during the maturation of fruiting bodies.

Ethanol Catabolism in Corynebacterium glutamicum

Corynebacterium glutamicum grows on a variety of carbohydrates and organic acids as single or combined sources of carbon and energy. Here we show the ability of C. glutamicum to grow on ethanol with growth rates up to 0.24 h(-1) and biomass yields up to 0.47 g dry weight (g ethanol)(-1). Mutants of C. glutamicum deficient in phosphotransacetylase (PTA), isocitrate lyase (ICL) and malate synthase (MS) were unable to grow on ethanol, indicating that acetate activation and the glyoxylate cycle are essential for utilization of this substrate. In accordance, the expression profile of ethanol-grown C. glutamicum cells compared to that of glucose-grown cells revealed an increased expression of genes encoding acetate kinase (AK), PTA, ICL and MS. Furthermore, the specific activities of these four enzymes as well as those of alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) were found to be high in ethanol-grown and low in glucose-grown cells. Growth of C. glutamicum on a mixture of glucose and ethanol led to a biphasic growth behavior, which was due to the sequential utilization of glucose before ethanol. Accordingly, the specific activities of ADH, ALDH, AK, PTA, ICL and MS in cells grown in medium containing both substrates were as low as in glucose-grown cells in the first growth phase, but increased 5- to 100-fold during the second growth phase. The results indicate that ethanol catabolism in C. glutamicum is subject to carbon source-dependent regulation, i.e., to a carbon catabolite control.

Ability to grow on lipids accounts for the fully virulent phenotype in neutropenic mice of Aspergillus fumigatus null mutants in the key glyoxylate cycle enzymes

Incidence and mortality rates of invasive aspergillosis clearly indicate the need of novel antifungals to treat patients suffering from this disease. Fungal proteins playing a crucial role in pathogenesis and with no orthologue in human cells are considered as primary therapeutic targets for the development of new antifungals with a high therapeutic index, one of the major drawbacks of the standard antifungal therapy, so far. In this work, we have analyzed the role in pathogenesis of the key enzymes of the Aspergillus fumigatus glyxoxylate cycle, isocitrate lyase and malate synthase, two possible candidates to primary therapeutic targets in this fungus. Deletion strains lacking isocitrate lyase (DeltaacuD strains) or malate synthase (DeltaacuE mutants) were constructed in this work. The Neurospora crassa pyr-4 gene was used as the replacing marker in gene deletion experiments. The pathogenicities of DeltaacuD and DeltaacuE mutants were tested in neutropenic mice and compared with those of two reference wild-type isolates A. fumigatus 237 and A. fumigatus 293. Interestingly, virulence and cytological studies clearly indicated the dispensability of the A. fumigatus glyoxylate cycle for pathogenicity. In addition, these results suggested the suitability of the pyr-4 gene as a valuable replacing marker for virulence studies in this fungus, a fact that was further confirmed by gene expression analyses. Finally, growth tests were performed to investigate the germination and growth of the DeltaacuD and DeltaacuE strains in nutrient deprivation environments, resembling the conditions that A. fumigatus conidia face after phagocytosis. Results obtained in this work strongly suggest that the ability to grow on lipids (triglycerides) of A. fumigatus isocitrate lyase and malate synthase deletion strains accounts for their fully virulent phenotype.