A dansyl-derivatized phytic acid analogue as a fluorescent substrate for phytases: experimental and computational approach

A new myo-inositol pentakisphosphate was synthesized, which featured a dansyl group at position C-5. The fluorescent tag was removed from the inositol by a 6-atom spacer to prevent detrimental steric interactions in the catalytic site of phytases. The PEG linker was used in order to enhance hydrophilicity and biocompatibility of the new artificial substrate. Computational studies showed a favorable positioning in the catalytic site of phytases. Enzymatic assays demonstrated that the tethered myo-inositol was processed by two recombinant phytases Phy-A and Phy-C, classified respectively as acid and alkaline phytases, with similar rates of phosphate release compared to their natural substrate.

Wine Thermosensitive Proteins Adsorb First and Better on Bentonite during Fining: Practical Implications and Proposition of Alternative Heat Tests

Bentonite fining is the most popular treatment used to remove proteins in white and rosé wines. The usual heat test used to adjust the bentonite dose consists of heating the wine during 30 min at 80 °C. At this temperature, all of the proteins are unfolded, and this can lead to an overestimation of the dose. We have shown that proteins adsorb on bentonite in a specific order and, more importantly, that the proteins responsible for haze formation adsorb first. Fluorescence spectroscopy showed that this is due to the structural properties of proteins, which can be classified as hard and soft proteins. Alternative heat tests were performed at a lower temperature (40 °C) and showed a better correlation with accelerated aging. These tests were also less dependent upon the wine pH.

NMR structure of rALF-Pm3, an anti-lipopolysaccharide factor from shrimp: model of the possible lipid A-binding site

The anti-lipopolysaccharide factor ALF-Pm3 is a 98-residue protein identified in hemocytes from the black tiger shrimp Penaeus monodon. It was expressed in Pichia pastoris from the constitutive glyceraldehyde-3-phosphate dehydrogenase promoter as a folded and (15)N uniformly labeled rALF-Pm3 protein. Its 3D structure was established by NMR and consists of three alpha-helices packed against a four-stranded beta-sheet. The C(34)-C(55) disulfide bond was shown to be essential for the structure stability. By using surface plasmon resonance, we demonstrated that rALF-Pm3 binds to LPS, lipid A and to OM-174, a soluble analogue of lipid A. Biophysical studies of rALF-Pm3/LPS and rALF-Pm3/OM-174 complexes indicated rather high molecular sized aggregates, which prevented us to experimentally determine by NMR the binding mode of these lipids to rALF-Pm3. However, on the basis of striking structural similarities to the FhuA/LPS complex, we designed an original model of the possible lipid A-binding site of ALF-Pm3. Such a binding site, located on the ALF-Pm3 beta-sheet and involving seven charged residues, is well conserved in ALF-L from Limulus polyphemus and in ALF-T from Tachypleus tridentatus. In addition, our model is in agreement with experiments showing that beta-hairpin synthetic peptides corresponding to ALF-L beta-sheet bind to LPS. Delineating lipid A-binding site of ALFs will help go further in the de novo design of new antibacterial or LPS-neutralizing drugs.

Overexpression of ovine leptin inPichia pastoris: physiological yeast response to leptin production and characterization of the recombinant hormone

Ovine leptin was cloned in the methylotrophic yeast Pichia pastoris using a pPIC9K vector. Leptin was produced and secreted into the culture medium using the Saccharomyces cerevisiae alpha-mating factor prepro signal by five clones. Expression levels of leptin varied from clone to clone, depending on the copy number of the ob gene. Highest expression was observed with the single-copy clone S27 (250 mg/l). The modifications of culture conditions in batch and fed-batch culture increase the yield of protein. The use of higher cell concentration (63 g/l) before induction of oLept associate with a regulation of pH at 3.2, which decreases the effects of proteolysis, increases the expression level of the oLept to 402 mg/l. Moreover, compared with the non-producer clone, we observed a drastic decrease in growth rate and biomass yield in the leptin-producing clones. At the end of the fed-batch phase at pH 3.2 with clone S27, mortality rate reached 17.3%. Results showed that recombinant leptin production induced metabolic stress, and a negative impact on biomass yield and growth rate. We characterized the recombinant leptin produced by clone S27. It exhibited a molecular mass of 16 kDa, an N-terminal amino acid sequence identical to that of ovine leptin but with an additional tyrosine introduced by the cloning site. Moreover, it was found to be biologically active in vitro. The available production of a large quantity of oLept will strengthen the functional study for theoretical and practical purposes.

Purification and characterization of an intracellular beta-glucosidase from a Candida sake strain isolated from fruit juices

A yeast strain isolated in the laboratory from fruit juices was studied and classified as Candida sake. The strain produces an intracellular beta-glucosidase when grown with cellobiose as the carbon source. The enzyme was purified by ion-exchange chromatography and gel filtration. The molecular mass of the purified intracellular beta-glucosidase, estimated by gel filtration, was 240 kDa. The tetrameric structure of the beta-glucosidase was determined following treatment of the purified enzyme with sodium dodecyl sulfate. The enzyme exhibited optimum activity at 52 degrees C and pH 4.25 with citrate-phosphate buffer. The enzyme was active against soluble glycosides with the (1-->4)-beta configuration, and from Lineweaver Burk plots, a Km value of 6.9 mmol/L was found for p-nitrophenyl-beta-D-glucopyranoside. The beta-glucosidase was found to be tolerant to glucose inhibition with a Ki value of 0.2 mol/L.

A very stable beta-glucosidase from a Candida molischiana mutant strain: enzymatic properties, sequencing, and homology with other yeast beta-glucosidases

We purified a beta-glucosidase from the mutant strain Candida molischiana 35M5N. Analysis of the kinetic properties of this enzyme did not show any differences between the previously purified wild-type enzyme and that of the mutant. Nevertheless, a study of the stability of the enzyme at different pH levels and temperatures showed the increase resistance of this protein. This enzyme was found to be stable at pH 5 for 145 h and retained 78% of its initial activity after the same time at pH 3.5 (optimal pH) and 30 degrees C. This difference between the wild-type and the mutant enzyme could be explained by differences in the quantity or quality of glycosylation. This glycoprotein showed different forms after deglycosylation. Some peptides from this protein were also sequenced. An homology analysis found similarities between this beta-glucosidase and beta-glucosidases of Candida pelliculosa and Schizophyllum commune.

Purification and characterization of the endocellular beta-glucosidase of a new strain of Candida entomophila isolated from fermenting agave (Agave sp.) juice

A yeast strain isolated in the laboratory from fermenting agave (Agave sp.) juice was studied and classified as Candida entomophila. The beta-glucosidase of this yeast was purified by ion-exchange chromatography and gel filtration. Its molecular mass estimated by gel filtration was 400 kDa. The oligomeric structure was determined following treatment of the purified enzyme with SDS. Its optimum pH was between 5 and 6, and its optimum temperature was 60 degrees C. The enzyme was active against soluble glucosides with (1-->3)-beta, (1-->4)-beta and (1-->4)-alpha linkage configuration, and it possesses (1-->6)-alpha-arabinofuranosidase activity. It is competitively inhibited by glucose and by D-gluconic acid lactone. The enzyme was constitutive and a glucosyltransferase activity is observed in the presence of ethanol. Since the glycosides present in wines and fruit juices represent a potential source of aromatic flavour, the possible use of the yeast glucosidase for the liberation of the bound aroma is discussed.

Purification and properties of the endocellular beta-glucosidase of Candida cacaoi Buckley and Van Uden CBS 2020

The endocellular enzyme beta-glucosidase of Candida cacaoi was purified by ion-exchange chromatography and gel filtration. The molecular weight was 220 +/- 10 kDa; its optimum pH was between 4 and 5.5 and its optimum temperature was 60 degrees C. This enzyme was active against soluble glucosides tested with beta(1-2), beta(1-3), beta(1-4) and even alpha(1-4) and alpha(1-6) and was inhibited by D-glucono-delta-lactone. The enzyme was constitutive but its synthesis was repressed by glucose.

Comparison of the properties of the purified beta-glucosidase from the transformed strain of Saccharomyces cerevisiae TYKF2 with that of the donor strain Kluyveromyces fragilis Y610

Saccharomyces cerevisiae TYKF2 was obtained by cloning in S. cerevisiae the gene coding for beta-glucosidase in Kluyveromyces fragilis Y610 (ATCC 12424). The beta-glucosidases of both organisms were purified and their biochemical characteristics were determined. The two beta-glucosidases had the same enzymatic properties as those previously described in the literature. The strain S. cerevisiae TYKF2 is able to produce enhanced amounts of enzyme.

Biosynthesis regulation of the beta-glucosidase produced by a yeast strain transformed by genetic engineering

The biosynthesis of the beta-glucosidase enzyme was studied in a transformed yeast obtained by cloning in Saccharomyces cerevisiae the structural gene coding for beta-glucosidase in Kluyveromyces fragilis. The enzyme biosynthesis was found to be non-adaptative, and repressed by glucose. These features are similar to those observed in K. fragilis. beta-Glucosidase activity in the transformed yeast was much higher than in K. fragilis. We attempted to ferment cellobiose with the transformed yeast: practically no cellobiose was consumed, growth and ethanol production were negligible. Warburg experiments showed that cellobiose fermentation did not occur when the respiratory chain was not functioning.