Synthesis of isopropyl-1-thio-beta-D-glucopyranoside (IPTGlc), an inducer of Aspergillus niger B1 beta-glucosidase production

Insulin and novel thioglycosides exert suppressive effect on human breast and colon carcinoma cells

The rationale for the implementation of novel therapies should be based on hallmarks of cancer. Two novel compounds labelled as thioglycoside A and B were designed and evaluated on breast and colon cancer cell lines. We assessed their cytotoxic effect after sensitizing cancer cells with insulin. In order to explore the underlying mechanisms, we performed tests to assess cell migration and motility, apoptosis, expression of glucose transporter 1 and proapoptotic proteins. Both compounds proved to have an antitumor effect which was significantly enhanced in combination with insulin. Linking glucose and anticancer agent presents an approach that exploits the Warburg effect. Targeting dysfunctional glycometabolism and increased glucose absorption is emerging as a promising anticancer strategy.

Transglucosidic reactions of the Aspergillus niger Family 3 β-glucosidase: Qualitative and quantitative analyses and evidence that the transglucosidic rate is independent of pH

The hydrolytic and transglucosidic reactions of the Aspergillus niger Family 3 beta-glucosidase were characterized. Michaelis-Menten plots of the rates of aglycone formation were normal (hyperbolic) at low [substrate]. However, at high [substrate] the rates decreased at pH below approximately 5.5 but increased at pH above approximately 5.5. Each decrease or increase took the form of a second hyperbola adjoining the first. Thin layer chromatography, gas-liquid chromatography, and NMR analyses indicated that the substrates became transglucosidic acceptors when present at high concentrations. When pNPGlc and cellobiose reacted as acceptors, the C6 hydroxyl of the non-reducing substrate component reacted to form beta-D-glucopyranosyl-(1-6)-beta-D-glucopyranosyl-p-nitrophenol and beta-D-glucopyranosyl-(1-6)-beta-D-glucopyranosyl-(1-4)-D-glucopyranose, respectively. The acceptor action accounted for the second adjoining hyperbolas. Rate equations were derived for the production of the aglycone and the transglucosidic intermediate, and these equations described the data very well. Hydrolytic Vmax {Vmax(h)}, hydrolytic Km {Km(h)}, transglucosidic Vmax {Vmax(t)}, and transglucosidic Km {Km(t)} values were obtained by non-linear regression analysis using these equations. Vmax(h) pH profiles were bell shaped with optima between pH 4 and 4.5 but the Vmax(t) values did not change substantially between pH 3 and 7. These differences in the pH profiles explain the decreasing and increasing adjoining hyperbolas since Vmax(t) is lower than Vmax(h) at pH less than approximately 5.5 but higher than Vmax(h) at pH greater than approximately 5.5. The reason for these pH effects is that the value of the hydrolytic rate constant (k3) decreases while the value of the transglucosidic rate constant (k4) does not change between pH 3 and 7. The study also showed that gentiobiose forms by an intermolecular reaction of the C6 hydroxyl of Glc rather than an intramolecular reaction and that an equatorial orientation of the C2 hydroxyl, the presence of a C6 primary hydroxyl and beta-linkages with oligosaccharide acceptors are important for acceptor reactivity.

Manipulating volatile emission in tobacco leaves by expressing Aspergillus nigerbeta-glucosidase in different subcellular compartments

Expression of the Aspergillus nigerbeta-glucosidase gene, BGL1, in Nicotiana tabacum plants (cv. Xanthi) had a profound effect on the volatile emissions of intact and crushed leaves. BGL1 was expressed under the control of the cauliflower mosaic virus (CaMV) 35S promoter and targeted to the cytoplasm, cell wall, lytic vacuole (LV), chloroplast or endoplasmic reticulum (ER). Subcellular localization was confirmed by gold immunolabelling, followed by transmission electron microscopy (TEM). Significant beta-glucosidase activity was observed in transgenic plants expressing BGL1 in the cell wall, LV and ER. Compared with controls, all intact transgenic leaves were found to emit increased levels of 2-ethylhexanol, as determined by gas chromatography-mass spectrometry (GC-MS) analysis of the headspace volatiles. Plants expressing BGL1 in the cell wall (Tcw) emitted more trans-caryophyllene than did non-transgenic controls, whereas plants expressing BGL1 in the ER (Ter) and LV (Tvc) emitted more cembrene than did non-transgenic controls. Volatiles released from crushed transgenic leaves and collected with solid-phase microextraction (SPME) polydimethylsiloxane fibre were distinctly enhanced. Significant increases in linalool, nerol, furanoid cis-linalool oxide, 4-methyl-1-pentanol, 6-methyl-hept-5-en-2-ol and 2-ethylhexanol were detected in transgenic plants when compared with wild-type controls. 3-Hydroxyl-beta-ionone levels were increased in crushed Tcw and Ter leaves, but were undetectable in Tvc leaves. The addition of glucoimidazole, a beta-glucosidase inhibitor, abolished the increased emission of these volatiles. These results indicate that the expression of a fungal beta-glucosidase gene in different subcellular compartments has the potential to affect the emission of plant volatiles, and thereby to modify plant-environment communication and aroma of agricultural products.

Influence of exo beta-D-galactofuranosidase inhibitors in cultures of Penicillium fellutanum and modifications in hyphal cell structure

We have examined beta-D-galactofuranosidase production by Penicillium fellutanum in the presence of D-galactono-1,4-lactone or 4-aminophenyl 1-thio-beta-D-galactofuranoside, two potent in vitro inhibitors of the enzyme. Activity of the enzyme in the culture filtrate was increased by 35% when glucose was replaced by D-galactose as the carbon source, and the activity diminished 80% of the control value when the inhibitors were added. Significant alterations of the culture were observed: (a) the medium became increasingly opalescent due to the secretion of a protein aggregate (PA) which contained 15% neutral sugar, mainly ribose; (b) the peptidophosphogalactomannan (pPGM) containing galactofuranose, normally produced by P. fellutanum, could not be obtained from the culture medium in the presence of the inhibitors; (c) the content of galactofuranose in the cell wall was significantly decreased in the presence of D-galactono-1,4-lactone. The influence on the mycelia growth was investigated by light microscopy (LM) and transmission electron microscopy (TEM) showing important alterations.