Molecular structure of cyclomaltodextrinase derived from amylolytic lactic acid bacterium Enterococcus faecium K-1 and properties of recombinant enzymes expressed in Escherichia coli and Lactobacillus plantarum

Malto-oligosaccharides as critical functional ingredient: a review of their properties, preparation, and versatile applications

Malto-oligosaccharides (MOS) are α-1,4 glycosidic linked linear oligosaccharides of glucose, which have a diverse range of functional applications in the food, pharmaceutical, and other industries. They can be used to modify the physicochemical properties of foods thereby improving their quality attributes, or they can be included as prebiotics to improve their nutritional attributes. The degree of polymerization of MOS can be controlled by using specific enzymes, which means their functionality can be tuned for specific applications. In this article, we review the chemical structure, physicochemical properties, preparation, and functional applications of MOS in the food, health care, and other industries. Besides, we offer an overview for this saccharide from the perspective of prospect functional ingredient, which we feel lacks in the current literature. MOS could be expected to provide a novel promising substitute for functional oligosaccharides.

Investigating the role of carbohydrate-binding module 34 in cyclomaltodextrinase from Geobacillus thermopakistaniensis: structural and functional analyses

Carbohydrate-binding modules (CBMs) are noncatalytic regions found in several enzymes of glycoside hydrolase family 13 and are proposed to orient substrates to the catalytic site. In this study, a substantial information on the conserved aromatic residues in CBM34 regions of characterized bacterial cyclolmaltodextrinases (CDases) has been presented. Molecular modeling of CDase from Geobacillus thermopakistaniensis (CDase _Gt ) revealed a change in the active site geometry due to CBM34 truncation. The binding energies of full-length (CDase _Gt ) and CBM34 truncated (CDase _Gt -ΔN) models showed opposite trends. The least preferred substrate molecule by the full-length model was the most preferred by the CBM34 truncated one. These exciting in silico findings were experimentally verified by recombinant production and characterization of the full-length and the CBM34 truncated proteins. Both the enzymes showed similar optimum pH and temperature. However, substrate specificity was in the reverse order. These experimental verifications matched the homology modeling and docking predictions.

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The online version contains supplementary material available at 10.1007/s13205-021-03089-9.

An evolution-based designing and characterization of mutants of cyclomaltodextrinase: Molecular modeling and spectroscopic studies

Cyclomaltodextrinase (CDase) is a member of the alpha-amylase family GH13, the subfamily GH13_20. In addition to CDase and neopullulanase, this subfamily also contains maltogenic amylase. They have common structural features, but different substrate specificity. In current work, a combination of bioinformatics and experimental tools were used for designing and constructions of single and double mutants of a new variant of CDase from Anoxybacillus flavithermus. Considering the evolutionary variable positions 123 and 127 at the dimer interface of subunits in the alpha-amylase family, these positions in CDase were modified and three mutants, including A123V, C127Q and A123V/C127Q were constructed. The tertiary structure of WT and mutants were made with the MODELLER program, and the phylogenetic tree of homologous protein sequences was built with selected programs in Phylip package. Enzyme kinetic studies revealed that the catalytic efficiency of mutants, especially double one, is lower than the WT enzyme. Heat-induced denaturation experiments were monitored by measuring the UV/Vis signal at 280 nm, and it was found that WT protein is structurally more stable at 25 °C. However, it is more susceptible to changes in temperature compared to the double mutant. It was concluded that the positions 123 and 127 at the dimeric interface of CDase, not only could affect the conformational stability; but also; the catalytic properties of the enzyme by setting up the active site configuration in the dimeric state.

Optimizing the production of short and medium chain fatty acids (SCFAs and MCFAs) from waste activated sludge using different alkyl polyglucose surfactants, through bacterial metabolic analysis

Alkyl polyglucose is an environmentally-friendly biosurfactant, which is able to enhance short-chain fatty acids production with different carbon chain lengths and concentrations, during sludge anaerobic fermentation. This presents a promising strategy for sludge re-utilization by effectively converting hazardous sludge into value-added compounds. The maximum yield of short-chain fatty acids produced from sludge was 479.3 and 462.2 mg COD/g VSS, following pretreatment with APG06 and APG1214, respectively. To the best of our knowledge, the short-chain fatty acid production performance by sludge fermentation reported here, achieved a higher level than reported in previous studies. Additionally, these findings indicate that the production of medium-chain fatty acids from sludge can be induced by alkyl polyglucoses. Finally, the microbial community and enzyme activity were also assessed to reveal the mechanism of short-/medium-chain fatty acids biosynthesis under alkyl polyglucose pretreatment. This study demonstrates that alkyl polyglucose provides an environmentally-friendly and effective strategy for enhancing the production of short-/medium-chain fatty acids from waste activated sludge. These findings are useful for the assessment of alkyl polyglucose-assisted production of short-/medium-chain fatty acids, as well as for understanding the interactions between short-/medium-chain fatty acids and microbial communities with key enzymes, to establish short-/medium-chain fatty acids metabolic pathways during sludge fermentation.

Recombinant expression, purification, and characterization of a cyclodextrinase from Massilia timonae

Some microorganisms can produce cyclodextrin glycosyltransferases, which degrades starch by catalyzing cyclization and giving rise to cyclodextrin. Thus, to fully degrade starch, microorganisms can also synthesize cyclodextrinases, which hydrolyze cyclodextrins. In this work, a truncated gene, without the signal peptide coding sequence, encoding a cyclodextrinase from Massilia timonae was PCR amplified, cloned, and expressed in E. coli. The histidine-tagged recombinant enzyme was purified by immobilized metal ion affinity chromatography. The purified protein was found to be a tetramer of about 260 kDa, with monomers of about 65 kDa, as estimated by gel filtration and SDS-PAGE, respectively. The enzyme presented an optimum temperature of 40 °C, optimum pH of 7.0, and remained stable after 30 min of incubation at 45 °C, with a T₅₀ of 48.45 °C. The enzyme showed a higher activity toward β-cyclodextrin compared to that for maltodextrin and starch. K_M for β-cyclodextrin was 2.1 mM, V_max was 0.084 μmol/min, k_cat was 8326 min^-1, and k_cat/K_M was 4.1 × 10⁶ M^-1min^-1. Calcium acted as an activator and SDS, CTAB, several cations, and EDTA acted as strong inhibitors. The purified cyclodextrinase produced glucose and maltose as final products by hydrolysis of β-cyclodextrin, maltotetraose, and maltoheptaose. This novel cyclodextrinase could be a promising alternative for the enzymatic hydrolysis of starch.