Factors influencing the formation and stability of D-glucoside 3-dehydrogenase activity in cultures of Agrobacterium tumefaciens

Gene cloning and expression of a glucoside 3-dehydrogenase from Sphingobacterium faecium ZJF-D6, and used it to produce N-p-nitrophenyl-3-ketovalidamine

In this study, we report the cloning and expression of a functional glucoside 3-dehydrogenase (G3DH) gene from Sphingobacterium faecium ZJF-D6. This gene is 1686 bp in length and encodes a peptide of 562 amino acids. The G3DH gene was successfully expressed in E. coli, and the recombinant enzyme could oxidize glucosides, galactosides and analogues at C-3 position. The sequence and multiple alignment analysis showed that the enzyme has highest identity with G3DHs from Paraglaciecola polaris LMG 21857, Aliiglaciecola lipolytica E3 and Halomonas sp. alpha-15. The recombinant G3DH was purified on Ni-NTA column and exhibited the highest activity at pH 7.6 and 30 °C. It was sensitive to acid and alkali, and showed well thermostability. The SfG3DH could oxidize a wild range of sugars. When recombinant E. coli BL21 cells were used as catalyst, a high rate of conversion to N-p-nitrophenyl-3-ketovalidamine was achieved, and no p-nitroaniline was detected. This process offers a promising approach to fulfill substrate of 3-ketovalidoxylamine A C-N lyase production.

Screening of a glucoside 3-dehydrogenase-producing strain, Sphingobacterium faecium, based on a high-throughput screening method and optimization of the culture conditions for enzyme production

The objective of this study was to screen glucoside 3-dehydrogenase (G3DH)-producing strain based on a high-throughput G3DH screening method. Optimization of culture conditions of the isolated strain was also applied in this study. This screening method employed electron transfer reaction in 96-well microtiter plates, α-methyl-D-glucoside, galactose, 2-deoxy-D-glucose, and 3-O-methyl-D-glucose were used as substrates. Using this screening method, one out of 78 strains isolated from different soil samples was obtained with high G3DH activity. The accuracy of the screening method was proved by alkaline treatment analysis of 3-keto sugars. The isolated strain was identified as Sphingobacterium faecium ZJF-D6 by phenotypic characterization and 16S rDNA sequence analysis. The culture conditions of S. faecium for G3DH production were optimized. Sucrose was found as the most suitable carbon source for the G3DH production. The highest G3DH production and cell growth were achieved using the medium at the initial pH of 7.0 at 25 °C for 36 h with activity of 8.03 × 10(-2) U/mL culture. This strain appears promising for potential application in the industry to produce 3-keto sugars. To our knowledge, this is the first report on S. faecium for G3DH production. The method described herein represents a useful tool for the high-throughput isolation of G3DH.

The catabolism of 3-ketolactose in Agrobacterium

The existence of a novel enzyme, catalyzing the hydrolysis of 3-ketolactose, is described in the different genetic groups of the genus Agrobacterium. The enzyme differs from the other glycosidases formed by Agrobacterium during growth on lactose. The inducibility of the enzyme could be demonstrated in a strain from biotype 1, but not in a strain from biotype 2. The specific activity of the 3-ketolactose hydrolase is higher in extracts of strains belonging to biotype 2 than to biotype 1. The optimum pH of the enzyme in Tris-HCl buffer is 8.4-8.5. The K(m) value for 3-ketolactose is 2.2 × 10(-2) M. The 3-ketolactose hydrolase is stimulated by Mg(2+) and Mn(2+), and inhibited by Zn(2+). Mercaptoethanol promotes the reaction rate in extracts of strains of biotype 1 but not in extracts of strains of bio-type 2.

Purification and characterization of the glucoside 3-dehydrogenase produced by a newly isolated Stenotrophomonas maltrophilia CCTCC M 204024

A soluble glucoside 3-dehydrogenase (G3DH) from Stenotrophomonas maltrophilia CCTCC M 204024, recently isolated from wheat soil in our laboratory, was purified to 37.4-fold with a yield of 24.7% and was estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a molecular mass of 66 kDa. 2,6-Dichlorophenolindophenol (DCPIP) and ferricyanide were able to act as artificial electron acceptors for the enzyme. The optimal pH of G3DH was in the range of 6.0-7.0 in the presence of DCPIP. The enzyme was stable in the pH range of 4.4-10.6 and was sensitive to heat. G3DH exhibited extremely broad substrate specificity by converting many sugars to their corresponding 3-ketoglucosides. They produced a characteristic spectrum by alkaline treatment with a peak at 340 nm. The apparent Km values for validoxylamine A and D: -glucose were 8.3 and 1.1 mM, respectively. Cu2+, Ag2+, and Hg2Cl2 inhibited the activity of G3DH.

Sucrose analogues modified at position 3: chemoenzymatic synthesis and inhibition studies of dextransucrases

Conditions for the large-scale (molar) oxidation of sucrose by Agrobacterium tumefaciens were improved, thus leading to homogeneous solutions of 3-ketosucrose in 40% yield. Treatment of this solution with hydroxylamine or methoxylamine afforded the corresponding oximes 3a and 3b (isolated as acetates) in excellent yield. Dissolving-metal reduction of these oximes gave mixtures of amino disaccharides in which the gluco epimer (3-amino-3-deoxysucrose) was predominant. A more efficient approach to this amino sucrose was provided by the highly stereoselective hydrogenation of 3-ketosucrose peracetate (7), which gave exclusively the allo isomer 8 (2,4,6-tri-O-acetyl-alpha-D-allopyranosyl 1,3,4,6-tetra-O-acetyl-beta-D-fructofuranoside). Upon reaction with lithium azide, the triflate derived from 8, compound 9, afforded 3-azido-3-deoxysucrose peracetate (10) which was converted into 3-amino-3-deoxysucrose (12). The reaction of triflate 9 with potassium ethylxanthate led to a mixture of products (the expected 3-S-ethoxythiocarbonyl-3-thiosucrose derivative and the peracetates of 3-thiosucrose and of 3-thiosucrose disulfide), which could be all converted into 3-thiosucrose (17). Sucrose analogues 12 and 17 were not substrates of dextransucrases from various strains of L. mesenteroides, nor did they participate in glycosyl transfer reactions to an acceptor (maltose). Compounds 3a and 12 were found to be strong competitive inhibitors of the dextran synthesis process (dextransucrase from strain B-1397). These results indicate that 3a and 12 compete effectively with sucrose for the sucrose binding site but are unable to participate as glycosyl donors in the polymerization or glycosyl-transfer processes.

Induction of D-aldohexoside:cytochrome c oxidoreductase in Agrobacterium tumefaciens

D-Aldohexopyranoside:cytochrome c oxidoreductase (ACO) was strongly induced by cellobiose, alpha-methylglucoside, beta-methylglucoside, kojibiose, and sophorose. Induction was rapid, and ACO was readily detectable within 10 min after addition of cellobiose as inducer. Although not measurable for 30 to 40 min after addition of inducer, once started, the rate of induction with alpha-methylglucoside equaled or even exceeded that obtained with cellobiose. Induction by sucrose, maltose, alpha-alpha-trehalose, melibiose, and lactose was weak. In general, the active ACO inducers were poor glycosidase inducers; the converse also appeared to be true. Although ACO induction was not repressed by D-glucose, it was repressed by succinate, malate, and fumarate.