Biochemical characterization and antioxidant and antiproliferative activities of different Ganoderma collections

The aim of this study was to conduct a molecular and biochemical characterization and to compare the antioxidant and antiproliferative activities of four Ganoderma isolates belonging to Ganoderma lucidum (Gl-4, Gl-5) and Ganoderma resinaceum (F-1, F-2) species. The molecular identification was performed by ITS and IGS sequence analyses and the biochemical characterization by enzymatic and proteomic approaches. The antioxidant activity of the ethanolic extracts was compared by three different methods and their flavonoid contents were also analyzed by high-performance liquid chromatography. The antiproliferative effect on U937 cells was determined by MTT assay. The studied mycelia differ both in the enzymatic activities and protein content. The highest content in total phenol and the highest antioxidant activity for DPPH free radical scavenging and chelating activity on Fe(2+) were observed with the Gl-4 isolate of G. lucidum. The presence of quercetin, rutin, myricetin, and morin as major flavonoids with effective antioxidant activity was detected. The ethanolic extracts from mycelia of G. lucidum isolates possess a substantial antiproliferative activity against U937 cells in contrast to G. resinaceum in which the antiproliferative effects were insignificant. This study provides a comparison between G. lucidum and G. resinaceum mycelial strains, and shows that G. resinaceum could be utilized to obtain several bioactive compounds.

Genomic profiling of carbohydrate metabolism in the ectomycorrhizal fungus Tuber melanosporum

• Primary carbohydrate metabolism plays a special role related to carbon/nitrogen exchange, as well as metabolic support of fruiting body development, in ectomycorrhizal macrofungi. In this study, we used information retrieved from the recently sequenced Tuber melanosporum genome, together with transcriptome analysis data and targeted validation experiments, to construct the first genome-wide catalogue of the proteins supporting carbohydrate metabolism in a plant-symbiotic ascomycete. • More than 100 genes coding for enzymes of the glycolysis, pentose phosphate, tricarboxylic acid, glyoxylate and methylcitrate pathways, glycogen, trehalose and mannitol metabolism and cell wall precursor were annotated. Transcriptional regulation of these pathways in different stages of the T. melanosporum lifecycle was investigated using whole-genome oligoarray expression data together with real-time reverse transcription-polymerase chain reaction analysis of selected genes. • The most significant results were the identification of methylcitrate cycle genes and of an acid invertase, the first enzyme of this kind to be described in a plant-symbiotic filamentous fungus. • A subset of transcripts coding for trehalose, glyoxylate and methylcitrate enzymes was up-regulated in fruiting bodies, whereas genes involved in mannitol and glycogen metabolism were preferentially expressed in mycelia and ectomycorrhizas, respectively. These data indicate a high degree of lifecycle stage specialization for particular branches of carbohydrate metabolism in T. melanosporum.

The Tuber borchii fruiting body-specific protein TBF-1, a novel lectin which interacts with associated Rhizobium species

Lectins, proteins that are able to bind carbohydrate structures, are typically involved in cell recognition mechanisms. We demonstrate here that TBF-1, the main soluble protein in the Tuber borchii Vittad. fruiting body, is a phase-specific lectin that is able selectively to bind the exopolysaccharides produced by ascoma-associated Rhizobium spp. Characterization of TBF-1 was performed using both the protein purified from the truffles and the recombinant protein overexpressed in Escherichia coli. The two proteins exhibit the same hemagglutination activity toward rabbit red blood cells and the same sugar binding specificity. The discovery of lectin activity for TBF-1 led us to propose revising the protein name to 'T. borchii fruiting body lectin 1' with the acronym TBFL-1.

Identification and characterization of the Tuber borchii D-mannitol dehydrogenase which defines a new subfamily within the polyol-specific medium chain dehydrogenases

A novel NADP(+)-dependent D-mannitol dehydrogenase and the corresponding gene from the plant symbiotic ascomycete fungus Tuber borchii was identified and characterized. The enzyme, called TbMDH, is a homotetramer with two zinc atoms per subunit. It catalyzed both D-fructose reduction and D-mannitol oxidation, although it showed the highest substrate specificity and catalytic efficiency for D-fructose. Co-factor specificity was restricted to NADP(H) and the reaction proceeded via a sequential ordered Bi Bi mechanism. The carbon responsive transcriptional pattern showed that Tbmdh is up-regulated when mycelia are transferred to a culture medium containing D-mannitol or D-fructose. The phylogenetic analysis showed TbMDH to be the first example of a fungal D-mannitol-2-dehydrogenase belonging to the medium-chain dehydrogenase/reductases (MDRs). The enzyme identified a new group of proteins, most of them annotated in databases as hypothetical zinc-dependent dehydrogenases, forming a distinct subfamily among the polyol dehydrogenase family.

The isoprenoid pathway in the ectomycorrhizal fungus Tuber borchii Vittad.: cloning and characterisation of the tbhmgr, tbfpps and tbsqs genes

The isoprenoid pathway of the ectomycorrhizal fungus Tuber borchii Vittad is investigated to better understand the molecular mechanisms at work, in particular during the maturation of the complex ascomata (the so-called "truffles"). Three T. borchii genes coding for the most important regulatory enzymes of the isoprenoid biosynthesis, 3-hydroxy-3-methylglutaryl-CoA reductase, farnesyl-diphosphate synthase (FPPS) and squalene synthase (SQS), were cloned and characterised. The analyses of their nucleotide and deduced amino acid sequences led us to identify the typical domains shown in homologous proteins. By using a quantitative real-time PCR the expression pattern of the three genes was analysed in the vegetative phase and during the complex ascoma maturation process, revealing an over-expression in the mature ascomata. The enzymatic activity of the T. borchii 3-hydroxy-3-methylglutaril-CoA reductase (HMGR) was investigated with a HPLC method, confirming that the significant isoprenoid biosynthesis in ripe ascomata proceeds not only via a transcriptional activation, but also via an enzyme activity control. These findings imply that isoprenoids play a fundamental role in Tuber ascomata, particularly in the last phases of their maturation, when they could be involved in antifungal or/and antimicrobial processes and contribute to the famous flavour of the truffle ascomata.

Novel and simple high-performance liquid chromatographic method for determination of 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity

We present here a high-performance liquid chromatographic method for the evaluation of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity. The automated method was applied to fungal and mouse liver extracts and validated by the addition of mevastatin to the reaction mixture and by several intra- and inter-day assays. This method offers important advantages over those previously reported because no radiolabeled substrates or expensive techniques such as mass spectrometry are required, and the time of analysis is relatively short. Moreover, the method can be successfully applied to different biological samples; hence, it should be very useful in evaluating potential inhibitors of the HMG-CoA enzyme and investigating cholesterol metabolism, cell growth and differentiation processes.

Tuber borchii fruit body: 2-dimensional profile and protein identification

The formation of the fruit body represents the final phase of the ectomycorrhizal fungus T. borchii life cycle. Very little is known concerning the molecular and biochemical processes involved in the fructification phase. 2-DE maps of unripe and ripe ascocarps revealed different protein expression levels and the comparison of the electropherograms led to the identification of specific proteins for each developmental phase. Associating micropreparative 2-DE to microchemical approaches, such as N-terminal sequencing and 2-D gel-electrophoresis mass-spectrometry, proteins playing pivotal roles in truffle physiology were identified.

Enolase from the ectomycorrhizal fungus Tuber borchii Vittad.: biochemical characterization, molecular cloning, and localization

Enolase from Tuber borchii mycelium was purified to electrophoretical homogeneity using an anion-exchange and a gel permeation chromatography. Furthermore, the corresponding gene (eno-1) was cloned and characterized. The purified enzyme showed a higher affinity for 2-PGA (0.26 mM) with respect to PEP; the stability and activity of enolase were dependent of the divalent cation Mg2+. T. borchii eno-1 has an ORF of 1323 bp coding for a putative protein of 440 amino acids and Southern blotting analysis revealed that the gene is present as a single copy in T. borchii. The enzymatic activity and the mRNA expression level evaluated in mycelia grown either in different carbon sources, in pyruvate or during starvation were the same in all the conditions tested, while biochemical and Northern blotting analyses performed with mycelia at different days of growth showed T. borchii eno-1 regulation in response to the growth phase. Finally, Western blotting analysis demonstrated that enolase is localized only in the cytosolic fraction confirming its important role in glycolysis.

Headspace solid-phase microextraction with gas chromatography and mass spectrometry in the investigation of volatile organic compounds in an ectomycorrhizae synthesis system

Ectomycorrhizae formation represents one of the most significant steps in the truffle life cycle and is determined by a complex molecular signaling between two symbionts. In order to understand the molecular pathway of ectomycorrhiza development, we focused on the signaling interaction between the ectomycorrhizal fungus Tuber borchii Vittad. and the Tilia americana L. plant roots. The medium of a pre-symbiotic (T. americana-T. borchii) in vitro system was analysed by headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry. In total, 73 volatile organic compounds (VOCs) were identified. Twenty-nine of these VOCs were produced only during the interaction phase between the two partners, leading to a hypothesis that these molecules might act as molecular messengers in order to pilot the ectomycorrhizae formation.

Identification of Tuber borchii Vittad. mycelium proteins separated by two-dimensional polyacrylamide gel electrophoresis using amino acid analysis and sequence tagging

This paper reports the first results in the proteome analysis of Tuber borchii Vittad. mycelium, an ectomycorrhizal fungus poorly defined genetically, but known for its generation of edible fruit bodies known as white truffles. Employing isoelectric focusing on immobilized pH gradients, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we obtained an electropherogram presenting over 800 spots within the window of isoelectric points (pI) 3.5-9 and a molecular mass of 10-200 kDa. Different reducing agents were tested in the sample preparation buffers, and the standard lysis buffer plus 2% w/v polyvinylpolypyrrolidone allowed the best solubilization and resolution of the proteins. The T. borchii proteins separated in micropreparative gels were electroblotted onto polyvinylidene difluoride membranes and visualized by Coomassie staining. Twenty-three proteins were excised and analyzed by the combination of amino acid and N-terminal analysis. One protein was identified by matching its amino acid composition, estimated isoelectric point and molecular mass against the SWISS-PROT and EMBL databases. Four spots were successfully tagged by Edman microsequencing but no homologous sequences were found in databases.

Three different forms of hexokinase are identified during Tuber borchii mycelium growth

Truffles are ectomycorrhizal fungi which have a great dependence on carbohydrates supplied by their host plants. The catabolism of hexoses in the mycobiont is important for the production of energy, and the first enzyme in the hexose assimilation pathways is hexokinase. This study reports differences in the expression of this enzyme during the growth of Tuber borchii Vittad. mycelium (strain ATCC 96540). Three hexokinase activities (HKM1, HKM2 and HKM3) were isolated by anion-exchange chromatography and partially purified. HKM1 and HKM2 were present in the linear phase at 15-50 days of growth. Two remarkable differences were found in the sugar-phosphorylating activity and stability of HKM1 and HKM2. HKM2 did not phosphorylate the fructose and it was present in the chromatographic profile only when substrates such as glucose, glucosamine or mannose were added to the extraction buffer. On the contrary, HKM1 utilized also fructose and was detected under all the experimental conditions used. HKM3 was the only molecular form observed after 70 days, when the fungus growth had reached a plateau. To our knowledge these results represent the first evidence for the presence in T. borchii mycelium of three distinct enzymatic forms of hexokinase which are differently expressed during growth of the fungus.

Separation of hexokinase activity using different hydrophobic interaction supports

Hydrophobic interaction chromatography (HIC) has been used extensively for the separation of proteins and peptides by elution using a descending salt gradient, with and without the use of detergents or denaturing agents. In this paper we compare different hydrophobic interaction chromatographic media for the separation of multiple forms of hexokinase from rabbit reticulocytes. Among the different hydrophobic chromatographic media tested (Toyopearl Phenyl 650S, Ether 650S and Butyl 650S) Toyopearl Phenyl 650S offered the best separation of multiple forms of hexokinase, probably due to its intermediate hydrophobicity. In order to establish the optimal experimental conditions, we evaluated the effects of different salts, and the results obtained demonstrated that among the antichaotropic salts, ammonium sulphate is the most suitable for the separation of hexokinase sub-types. The sample loading capacity of the three Toyopearl supports was investigated and the recovery of enzymatic activity obtained ranged from 60% to 90%, depending on the different salts and hydrophobic media used. The chromatographic profiles of hexokinase activity from various mammalian and fungal tissues also demonstrate that Toyopearl Phenyl 650S can be successfully employed for the separation of multiple forms of enzymes from different biological sources.

Rabbit brain hexokinase: evidence for the presence of two distinct molecular forms

In mammalian brain tissue, most hexokinase is bound to the mitochondria and only a small amount of the enzyme is present in soluble form. In this study we report that, in rabbit brain, hexokinase is present in two distinct molecular forms, which we designated HKH and HKL, both of which are separable using hydrophobic interaction or anion-exchange chromatography. These two molecular forms can be detected when hexokinase is prepared at pH 7.4, whereas at pH 10.0 only the more hydrophobic form, HKH, is present. The two subtypes of hexokinase do not show significant differences in Km values for glucose and ATP, in Ki values for glucose-6-phosphate or in their molecular weights. HKH is able to rebind mitochondrial membranes, while HKL has lost this ability, suggesting that the hydrophobic peptide at the N-terminal has been removed. The susceptibility of the N-terminal peptide to proteolysis is completely inhibited by using antiproteolytic compounds, such as leupeptin or E-64. The results reported in this paper suggest that a cysteine protease, probably belonging to a the class of cathepsins, may be involved in the processing of bindable hexokinase to the non-bindable form in rabbit brain, and that the activity of this protease is pH-dependent.