Efficient chemoenzymatic synthesis of 4-nitrophenyl β-d-apiofuranoside and its use in screening of β-d-apiofuranosidases

Acuminosylation of Tyrosol by a Commercial Diglycosidase

A commercial glycosidase mixture obtained from Penicillium multicolor (Aromase H2) was found to comprise a specific diglycosidase activity, β-acuminosidase, alongside undetectable levels of β-apiosidase. The enzyme was tested in the transglycosylation of tyrosol using 4-nitrophenyl β-acuminoside as the diglycosyl donor. The reaction was not chemoselective, providing a mixture of Osmanthuside H and its counterpart regioisomer 4-(2-hydroxyethyl)phenyl β-acuminoside in 58% yield. Aromase H2 is therefore the first commercial β-acuminosidase which is also able to glycosylate phenolic acceptors.

Synthesis of Tyrosol and Hydroxytyrosol Glycofuranosides and Their Biochemical and Biological Activities in Cell-Free and Cellular Assays

Tyrosol (T) and hydroxytyrosol (HOT) and their glycosides are promising candidates for applications in functional food products or in complementary therapy. A series of phenylethanoid glycofuranosides (PEGFs) were synthesized to compare some of their biochemical and biological activities with T and HOT. The optimization of glycosylation promoted by environmentally benign basic zinc carbonate was performed to prepare HOT α-L-arabino-, β-D-apio-, and β-D-ribofuranosides. T and HOT β-D-fructofuranosides, prepared by enzymatic transfructosylation of T and HOT, were also included in the comparative study. The antioxidant capacity and DNA-protective potential of T, HOT, and PEGFs on plasmid DNA were determined using cell-free assays. The DNA-damaging potential of the studied compounds for human hepatoma HepG2 cells and their DNA-protective potential on HepG2 cells against hydrogen peroxide were evaluated using the comet assay. Experiments revealed a spectrum of different activities of the studied compounds. HOT and HOT β-D-fructofuranoside appear to be the best-performing scavengers and protectants of plasmid DNA and HepG2 cells. T and T β-D-fructofuranoside display almost zero or low scavenging/antioxidant activity and protective effects on plasmid DNA or HepG2 cells. The results imply that especially HOT β-D-fructofuranoside and β-D-apiofuranoside could be considered as prospective molecules for the subsequent design of supplements with potential in food and health protection.

Apiose-Relevant Glycosidases

Apiose is a branched pentose naturally occurring either as a component of the plant cell wall polysaccharides or as a sugar moiety present in numerous plant secondary metabolites such as flavonoid and phenylethanoid glycosides, substrates in plant defense systems or as glycosylated aroma precursors. The enzymes catalyzing hydrolysis of such apiosylated substances (mainly glycosidases specific towards apiose or acuminose) have promising applications not only in hydrolysis (flavor development), but potentially also in the synthesis of apiosides and apioglucosides with pharmaceutical relevance. This review summarizes the actual knowledge of glycosidases recognizing apiose and their potential application in biocatalysis.

Off-line two-dimensional liquid chromatography separation for the quality control of saponins samples from Quillaja Saponaria

Quil-A is a purified extract of saponins with strong immunoadjuvant activity. While specific molecules have been identified and tested in clinical trials, Quil-A is mostly used as a totum of the Quillaja Saponaria bark extract. Quality control of the extract stability is usually based on the monitoring of specific saponins, whereas the comparison of samples with an initial chromatogram seems more appropriate. A reference fingerprint based on comprehensive two-dimensional liquid chromatography offers a rapid detection of nonconform samples. To fulfill quality control constraints, off-line configuration using basic instrumentation was promoted. Hence, reversed-phase liquid chromatography × reversed-phase liquid chromatography and hydrophilic interaction chromatography × reversed-phase liquid chromatography methods with ultraviolet and single-quadrupole mass spectrometry detection were kinetically optimized. The reversed-phase liquid chromatography × reversed-phase liquid chromatography method used a pH switch between dimensions to maximize orthogonality. Despite diagonalization, it led to a high peak capacity of 831 in 2 h. On the other hand, the combination of hydrophilic interaction chromatography and reversed-phase liquid chromatography offered a larger orthogonality but a lower, yet satisfactory peak capacity of 673. The advantages of both methods were illustrated on degraded samples, where the reversed-phase liquid chromatography × reversed-phase liquid chromatography contour plot highlighted the loss of fatty acid chains, while the hydrophilic interaction chromatography × reversed-phase liquid chromatography method was found useful to evidence enzymatic loss of sugar moieties.

Apiin-induction of β-apiosidase production by Aspergillus sp. strains

β-Apiosidase is a rare glycosidase applied in winemaking for flavour enhancement. This enzyme is involved in the release of volatile terpenes by hydrolysis of their odourless glycosidic precursors. It is found as a minor component in commercial pectinase/cellulase preparations. Microbial production of β-apiosidase by two Aspergillus sp. strains was investigated. Apiin-induced production of this extracellular glycosidase was confirmed only during the cultivation of Aspergillus niger CBS 554.65 but the high productivity value reported in the work of Dupin et al. (1992) J. Agric. Food Chem. 40(10): 1886—1891 could not be reproduced. The achieved productivity was by far not satisfactory considering the apiin cost. Commercial enzyme preparations with β-apiosidase side-activity thus remain a better alternative as the enzyme source for biocatalytic applications.

Reaction mechanism of β-apiosidase from Aspergillus aculeatus

Apiosidases are glycosidases relevant for aroma development during fermentation of wines and black tea. Reaction mechanism of apiosidase from Aspergillus aculeatus in commercial glycanase Viscozyme L was studied by ¹H NMR technique. Study of hydrolysis of 4-nitrophenyl β-D-apiofuranoside revealed that this reaction proceeds with inversion of hydroxyl group in the anomeric center, which confirms inverting mechanism of the enzyme and its inability to catalyze transapiosylation in syntheses of apiosides.

Changes in the abundance of cell wall apiogalacturonan and xylogalacturonan and conservation of rhamnogalacturonan II structure during the diversification of the Lemnoideae

The diversification of the Lemnoideae was accompanied by a reduction in the abundance of cell wall apiogalacturonan and an increase in xylogalacturonan whereas rhamnogalacturonan II structure and cross-linking are conserved. The subfamily Lemnoideae is comprised of five genera and 38 species of small, fast-growing aquatic monocots. Lemna minor and Spirodela polyrhiza belong to this subfamily and have primary cell walls that contain large amounts of apiogalacturonan and thus are distinct from the primary walls of most other flowering plants. However, the pectins in the cell walls of other members of the Lemnoideae have not been investigated. Here, we show that apiogalacturonan decreased substantially as the Lemnoideae diversified since Wolffiella and Wolffia walls contain between 63 and 88% less apiose than Spirodela, Landoltia, and Lemna walls. In Wolffia, the most derived genus, xylogalacturonan is far more abundant than apiogalacturonan, whereas in Wolffiella pectic polysaccharides have a high arabinose content, which may arise from arabinan sidechains of RG I. The apiose-containing pectin rhamnogalacturonan II (RG-II) exists in Lemnoideae walls as a borate cross-linked dimer and has a glycosyl sequence similar to RG-II from terrestrial plants. Nevertheless, species-dependent variations in the extent of methyl-etherification of RG-II sidechain A and arabinosylation of sidechain B are discernible. Immunocytochemical studies revealed that pectin methyl-esterification is higher in developing daughter frond walls than in mother frond walls, indicating that methyl-esterification is associated with expanding cells. Our data support the notion that a functional cell wall requires conservation of RG-II structure and cross-linking but can accommodate structural changes in other pectins. The Lemnoideae provide a model system to study the mechanisms by which wall structure and composition has changed in closely related plants with similar growth habits.