Melibiose

About: Melibiose is a research topic. Over the lifetime, 1002 publications have been published within this topic receiving 27300 citations. The topic is also known as: Melibiose.

Characterization of Properties and Transglycosylation Abilities of Recombinant α-Galactosidase from Cold-Adapted Marine Bacterium Pseudoalteromonas KMM 701 and Its C494N and D451A Mutants.

Abstract: A novel wild-type recombinant cold-active α-d-galactosidase (α-PsGal) from the cold-adapted marine bacterium Pseudoalteromonas sp. KMM 701, and its mutants D451A and C494N, were studied in terms of their structural, physicochemical, and catalytic properties. Homology models of the three-dimensional α-PsGal structure, its active center, and complexes with D-galactose were constructed for identification of functionally important amino acid residues in the active site of the enzyme, using the crystal structure of the α-galactosidase from Lactobacillus acidophilus as a template. The circular dichroism spectra of the wild α-PsGal and mutant C494N were approximately identical. The C494N mutation decreased the efficiency of retaining the affinity of the enzyme to standard p-nitrophenyl-α-galactopiranoside (pNP-α-Gal). Thin-layer chromatography, matrix-assisted laser desorption/ionization mass spectrometry, and nuclear magnetic resonance spectroscopy methods were used to identify transglycosylation products in reaction mixtures. α-PsGal possessed a narrow acceptor specificity. Fructose, xylose, fucose, and glucose were inactive as acceptors in the transglycosylation reaction. α-PsGal synthesized -α(1→6)- and -α(1→4)-linked galactobiosides from melibiose as well as -α(1→6)- and -α(1→3)-linked p-nitrophenyl-digalactosides (Gal2-pNP) from pNP-α-Gal. The D451A mutation in the active center completely inactivated the enzyme. However, the substitution of C494N discontinued the Gal-α(1→3)-Gal-pNP synthesis and increased the Gal-α(1→4)-Gal yield compared to Gal-α(1→6)-Gal-pNP.

X-ray crystallography reveals molecular recognition mechanism for sugar binding in a melibiose transporter MelB.

Abstract: Major facilitator superfamily_2 transporters are widely found from bacteria to mammals. The melibiose transporter MelB, which catalyzes melibiose symport with either Na+, Li+, or H+, is a prototype of the Na+-coupled MFS transporters, but its sugar recognition mechanism has been a long-unsolved puzzle. Two high-resolution X-ray crystal structures of a Salmonella typhimurium MelB mutant with a bound ligand, either nitrophenyl-α-d-galactoside or dodecyl-β-d-melibioside, were refined to a resolution of 3.05 or 3.15 A, respectively. In the substrate-binding site, the interaction of both galactosyl moieties on the two ligands with MelBSt are virturally same, so the sugar specificity determinant pocket can be recognized, and hence the molecular recognition mechanism for sugar binding in MelB has been deciphered. The conserved cation-binding pocket is also proposed, which directly connects to the sugar specificity pocket. These key structural findings have laid a solid foundation for our understanding of the cooperative binding and symport mechanisms in Na+-coupled MFS transporters, including eukaryotic transporters such as MFSD2A. Guan and Hariharan report two crystal structures of melibiose transporter MelB in complex with substrate analogs, nitrophenyl-galactoside, and dodecyl-melibioside. Both structures revealed similar specific site for sugar recognition and resolved the cation-binding pocket, advancing the understanding of MelB and related transporters.

GROWTH OF Clostridium perfringens STRAINS ON α-GALACTOSIDES

Abstract: Five strains of Clostridium perfringens type A varied greatly in their ability to utilize and grow on the α-galactosides raffinose, stachyose, and melibiose when these sugars were added (1%) to a casein-digest medium. Stachyose and raffinose were utilized rapidly by NCTC strain 8798, and at moderate rate by NCTC strains 8238 and 10240. Strain KA3 utilized raffinose at moderate rates, but stachyose not at all. Strain FD-1 utilized raffinose only to a slight extent, and stachyose not at ail. NCTC strains 8238 and 10240 sporulated heavily during growth on raffinose and stachyose. The implications of these findings on previous work linking C. perfringens to legume-induced human flatulence is discussed.

Oligosaccharide synthesis by reversed catalysis using α-amylase from Bacillus licheniformis

Abstract: Evidence is provided for the synthesis of hetero-oligosaccharides by Termamyl, the thermotolerant α-amylase from Bacillus licheniformis. In the presence of soluble starch and added non-starch sugars (isomaltose, cellobiose, mannose, melibiose, stachyose, xylose and 1- o -methyl-β- d -glucopyranoside), oligosaccharides were produced by the reversed catalytic reaction. New peaks of homo- and hetero-oligosaccharides (DP1-10) were detected by high performance anion exchange chromatography (HPAEC) in equilibrium reaction mixtures. Attempts to increase the extent of synthesis of oligosaccharides using organic solvents (ethanol, methanol, N - propanol, propanediol, N - butanol, dioxane and dimethyl sulfoxide (DMSO)) to lower the water activity of the reaction mixture were unsuccessful. Raising the temperature of the reaction mixture from 37°C to 55°C was ineffective.