Hydrolysis and synthesis of branched cyclomaltohexaoses with Pseudomonas isoamylase

Ion mobility mass spectrometry enables the discrimination of positional isomers and the detection of conformers from cyclic oligosaccharides-metals supramolecular complexes

Cyclic oligosaccharides are well known to interact with various metals, able to form supramolecular complexes with distinct sizes and shapes. However, the presence of various isomers in a sample, including positional isomers and conformers, can significantly impact molecular recognition, encapsulation ability and chemical reactivity. Therefore, it is crucial to have tools for deep samples probing and correlation establishments. The emerging ion mobility mass spectrometry (IM-MS) has the advantages to be rapid and sensitive, but is still in its infancy for the investigation of supramolecular assemblies. In the herein study, it was demonstrated that IM-MS is suitable to discriminate several isomers of cyclodextrins (CD)-metals complexes, used as cyclic oligosaccharide models. In this sense, we investigated branched 6-O-α-glucosyl- or 6-O-α-maltosyl-β-cyclodextrins (G1-β-CD and G2-β-CD) and their purely cyclic isomers: CD8 (γ-CD) and CD9 (δ-CD). The corresponding collision cross section (CCS) values were deducted for the main positive singly and doubly charged species. Experimental CCS values were matched with models obtained from molecular modelling. The high mobility resolving power and resolution enabled discrimination of positional isomers, identification of various conformers and accurate relative content estimation. These results represent a milestone in the identification of carbohydrate conformers that cannot be easily reached by other approaches.

Investigation of debranching pattern of a thermostable isoamylase and its application for the production of resistant starch

Debranching enzymes contribute to the enzymatic production of resistant starch (RS) by reducing substrate molecular weight and increasing amylose yield. In the present study, the action pattern of a thermostable isoamylase-type debranching enzyme on different types of starch was investigated. The molecular weight distribution, glycosidic bond composition and contents of oligosaccharides released were monitored by various liquid chromatography techniques and nuclear magnetic resonance spectroscopy (NMR). These analyses showed that the isoamylase could specifically and efficiently attack α-1,6-glucosidic linkages at branch points, leaving the amylose favored by other amylolytic enzymes. Its ability to attack side chains composed of 1-3 glucose residues differentiates it from other isoamylases, a property which is also ideal for the RS preparation process. The enzyme was used as an auxiliary enzyme in the hydrolytic stage. The highest RS yield (53.8%) was achieved under the optimized conditions of 70 °C and pH 5.0, using 7 U isoamylase per g starch and 2 NU amylase per g starch. These data also help us better understand the application of isoamylase for preparation of other products from highly branched starch materials.

Application of ultra-high magnetic field for saccharide molecules: 1H NMR spectra of 6-O-α-d-glucopyranosyl-cyclomaltoheptaose and -cyclomaltohexaose

1H NMR spectra of G1-alpha-CD and G1-beta-CD were recorded using a spectrometer equipped with a 21.6 T magnet. An ultra-high magnetic field was effective for detecting 1H NMR signals with a small difference in chemical shifts. Introducing a glucosyl group onto CDs as a branch caused deformation of equilibrated 1H signals of cyclodextrin. Particularly, 1H signals in branched glucose were shifted greatly.

1H NMR spectra of branched-chain cyclomaltohexaoses (α-cyclodextrins)

The 1H NMR spectra of seven branched alpha-cyclodextrins (alpha-CDs) were observed and analyzed in detail. They were compared with spectra of alpha-CD and amylose. Although these branched alpha-CDs consist only of alpha-D-glucose with the same alpha-(1-->4) O-glucosyl binding, aside from one exception, differences in chemical shifts of corresponding signals were significantly large. Especially, differences in the chemical shift in anomeric protons were considerably large. Subtle differences in glucosyl binding directly influences chemical shifts of these protons because anomeric protons are located adjacent to the glucosyl binding sites.

Synthesis of branched cyclomaltooligosaccharide carboxylic acids (cyclodextrin carboxylic acids) by microbial oxidation

Novel branched cyclomaltooligosaccharide carboxylic acid (cyclodextrin carboxylic acid) derivatives were synthesized by microbial oxidation using Pseudogluconobacter saccharoketogenes to oxidize five types of branched cyclodextrins, including maltosyl beta-cyclodextrin (maltosyl-beta-CyD). For each novel cyclodextrin carboxylic acid derivative synthesized, the hydroxymethyl group of the terminal glucose residue in the branched part of the molecule was regiospecifically oxidized to a carboxyl group to give the corresponding uronic acid. In addition, the physicochemical properties of cyclomaltoheptaosyl-(6-->1)-alpha-D-glucopyranosyl-(4-->1)-alpha-D-glucopyranosiduronic acid (GUG-beta-CyD) (1) and its sodium salt were studied more extensively, as these compounds are most likely to have a practical application.

Properties of yeast debranching enzyme and its specificity toward branched cyclodextrins

Debranching enzyme was purified from Saccharomyces cerevisiae by DEAE-cellulose, omega-aminobutyl agarose and hydroxyapatite column chromatography. The activity of the eluent was monitored by the iodine-staining method which detects both the direct and indirect debranching enzymes. The elution profiles at every step showed a single peak with no shoulder. The crude and the purified enzyme preparations gave a single activity band with the same mobility on PAGE. The crude product produced 80% glucose compared to reducing sugar from glycogen-phosphorylase-limited dextrin while the partially purified and purified preparations produced 100% glucose. The activity of the purified enzyme was characterized and compared with that of the rabbit muscle enzyme by using various branched cyclodextrins as substrates. Both enzymes hydrolyzed 6-O-alpha-D-glucosyl cyclodextrins to glucose and cyclodextrins, but did not act on 6-O-alpha-maltosyl cyclomaltoheptaose. The yeast enzyme gave rise to glucose as a sole reducing sugar from 6-O-alpha-maltotriosyl cyclomaltoheptaose and 6-O-alpha-maltotetraosyl cyclomaltoheptaose, indicating that maltosyl and maltotriosyl transfers, respectively, had occurred, prior to the action of amylo-1,6-glucosidase. 6-O-alpha-D-Glucosyl cyclomaltoheptaose and 6-O-alpha-D-glucosyl cyclomalto-octaose, respectively, were better substrates than glycogen-phosphorylase-limited dextrin for the yeast and muscle enzymes. The yeast enzyme released glucose at a similar rate from 6-O-alpha-maltotriosyl cyclomaltoheptaose as from 6-O-alpha-maltotetraosyl cyclomaltoheptaose, but considerably lower rates than that from limit dextrin. The yeast debranching enzyme appears to be exclusively oligo-1,4----1,4-glucantransferase-amylo-1,6-glucosidase and does not have isoamylase.