Production, effects, and applications of fructans with various molecular weights

Fructan, a widespread functional polysaccharide, has been used in the food, pharmaceutical, cosmetic, and material production fields because of its versatile physicochemical properties and biological activities. Inulin from plants and levan from microorganisms are two of the most extensively studied fructans. Fructans from different plants or microorganisms have inconsistent molecular weights, and the molecular weight of fructan affects its properties, functions, and applications. Recently, increasing attention has been paid to the production and application of fructans having various molecular weights, and biotechnological processes have been explored to produce tailor-made fructans from sucrose. This review encompasses the introduction of extraction, enzymatic transformation, and fermentation production processes for fructans with diverse molecular weights. Notably, it highlights the enzymes involved in fructan biosynthesis and underscores their physiological effects, with a special emphasis on their prebiotic properties. Moreover, the applications of fructans with varying molecular weights are also emphasized.

Engineering the β-Fructofuranosidase Fru6 with Promoted Transfructosylating Capacity for Fructooligosaccharide Production

Levan-type fructooligosaccharides (FOS) exhibit enhanced health-promoting prebiotic effects on gut microbiota. The wild type (WT) of β-fructofuranosidase Fru6 could mainly yield 6-ketose. Semirational design and mutagenesis of Fru6 were exploited to promote the transfructosylating capacity for FOS. The promising variants not only improved the formation of 6-kestose but also newly produced tetrasaccharides of 6,6-nystose and 1,6-nystose (a new type of FOS), and combinatorial mutation boosted the production of 6-kestose and tetrasaccharides (39.9 g/L 6,6-nystose and 4.6 g/L 1,6-nystose). Molecular docking and molecular dynamics (MD) simulation confirmed that the mutated positions reshaped the pocket of Fru6 to accommodate bulky 6-kestose in a reactive conformation with better accessibility for tetrasaccharides formation. Using favored conditions, the variant S165A/H357A could yield 6-kestose up to 335 g/L, and tetrasaccharides (6,6-nystose and 1,6-nystose) reached a high level of 121.1 g/L (134.5 times of the mutant S423A). The β-(2,6)-linked FOS may show the potential application for the prebiotic ingredients.

New insights into the molecular mechanism behind mannitol and erythritol fructosylation by β-fructofuranosidase from Schwanniomyces occidentalis

The β-fructofuranosidase from Schwanniomyces occidentalis (Ffase) is a useful biotechnological tool for the fructosylation of different acceptors to produce fructooligosaccharides (FOS) and fructo-conjugates. In this work, the structural determinants of Ffase involved in the transfructosylating reaction of the alditols mannitol and erythritol have been studied in detail. Complexes with fructosyl-erythritol or sucrose were analyzed by crystallography and the effect of mutational changes in positions Gln-176, Gln-228, and Asn-254 studied to explore their role in modulating this biocatalytic process. Interestingly, N254T variant enhanced the wild-type protein production of fructosyl-erythritol and FOS by \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim$$\end{document}∼ 30% and 48%, respectively. Moreover, it produced neokestose, which represented \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim$$\end{document}∼ 27% of total FOS, and yielded 31.8 g l⁻¹ blastose by using glucose as exclusive fructosyl-acceptor. Noteworthy, N254D and Q176E replacements turned the specificity of Ffase transferase activity towards the synthesis of the fructosylated polyols at the expense of FOS production, but without increasing the total reaction efficiency. The results presented here highlight the relevance of the pair Gln-228/Asn-254 for Ffase donor-sucrose binding and opens new windows of opportunity for optimizing the generation of fructosyl-derivatives by this enzyme enhancing its biotechnological applicability.

Molecular insight into regioselectivity of transfructosylation catalyzed by GH68 levansucrase and β-fructofuranosidase

Glycoside hydrolase family 68 (GH68) enzymes catalyze β-fructosyltransfer from sucrose to another sucrose, the so-called transfructosylation. Although regioselectivity of transfructosylation is divergent in GH68 enzymes, there is insufficient information available on the structural factor(s) involved in the selectivity. Here, we found two GH68 enzymes, β-fructofuranosidase (FFZm) and levansucrase (LSZm), encoded tandemly in the genome of Zymomonas mobilis, displayed different selectivity: FFZm catalyzed the β-(2→1)-transfructosylation (1-TF), whereas LSZm did both of 1-TF and β-(2→6)-transfructosylation (6-TF). We identified His79^FFZm and Ala343^FFZm and their corresponding Asn84^LSZm and Ser345^LSZm respectively as the structural factors for those regioselectivities. LSZm with the respective substitution of FFZm-type His and Ala for its Asn84^LSZm and Ser345^LSZm (N84H/S345A-LSZm) lost 6-TF and enhanced 1-TF. Conversely, the LSZm-type replacement of His79^FFZm and Ala343^FFZm in FFZm (H79N/A343S-FFZm) almost lost 1-TF and acquired 6-TF. H79N/A343S-FFZm exhibited the selectivity like LSZm but did not produce the β-(2→6)-fructoside-linked levan and/or long levanooligosaccharides that LSZm did. We assumed Phe189^LSZm to be a responsible residue for the elongation of levan chain in LSZm and mutated the corresponding Leu187^FFZm in FFZm to Phe. An H79N/L187F/A343S-FFZm produced a higher quantity of long levanooligosaccharides than H79N/A343S-FFZm (or H79N-FFZm), although without levan formation, suggesting that LSZm has another structural factor for levan production. We also found that FFZm generated a sucrose analog, β-D-fructofuranosyl α-D-mannopyranoside, by β-fructosyltransfer to d-mannose and regarded His79^FFZm and Ala343^FFZm as key residues for this acceptor specificity. In summary, this study provides insight into the structural factors of regioselectivity and acceptor specificity in transfructosylation of GH68 enzymes.

Insight into the effects and biotechnological production of kestoses, the smallest fructooligosaccharides

Kestoses, the smallest fructooligosaccharides, are trisaccharides composed of a fructose molecule and a sucrose molecule linked by either β-(2,1) or β-(2,6) linkage. 1-kestose, 6-kestose and neokestose are the three types of kestoses occurring in nature. As the main kind of fructooligosaccharide, kestoses share similar physiological effects with other fructooligosaccharides, and they have recently been determined to show more notable effects in promoting the growth of probiotics including Faecalibacterium prausnitzii and Bifidobacterium than those of other fructooligosaccharides. Kestoses exist in many plants, but the relatively low content and the isolation and purification are the main barriers limiting their industrial application. The production of kestoses by enzymatic biosynthesis and microbial fermentation has the potential to facilitate its production and industrial use. In this article, the recent advances in the research of kestoses were overviewed, including those studying their functions and production. Kestose-producing enzymes were introduced in detail, and microbial production and fermentation optimization techniques for enhancing the yield of kestoses were addressed. β-Fructofuranosidase is the main one used to produce kestoses because of the extensive range of microbial sources. Therefore, the production of kestoses by microorganisms containing β-fructofuranosidase has also been reviewed. However, few molecular modification studies have attempted to change the production profile of some enzymes and improve the yield of kestoses, which is a topic that should garner more attention. Additionally, the production of kestoses using food-grade microorganisms may be beneficial to their application in the food industry.

Tailored Enzymatic Synthesis of Chitooligosaccharides with Different Deacetylation Degrees and Their Anti-Inflammatory Activity

By controlled hydrolysis of chitosan or chitin with different enzymes, three types of chitooligosaccharides (COS) with MW between 0.2 and 1.2 kDa were obtained: fully deacetylated (fdCOS), partially acetylated (paCOS), and fully acetylated (faCOS). The chemical composition of the samples was analyzed by high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and MALDI-TOF mass spectrometry. The synthesized fdCOS was basically formed by GlcN, (GlcN)2, (GlcN)3, and (GlcN)4. On the contrary, faCOS contained mostly GlcNAc, (GlcNAc)2 and (GlcNAc)3, while paCOS corresponded to a mixture of at least 11 oligosaccharides with different proportions of GlcNAc and GlcN. The anti-inflammatory activity of the three COS mixtures was studied by measuring their ability to reduce the level of TNF-α (tumor necrosis factor) in murine macrophages (RAW 264.7) after stimulation with a mixture of lipopolysaccharides (LPS). Only fdCOS and faCOS were able to significantly reduce the production of tumor necrosis factor (TNF)-α at 6 h after stimulation with lipopolysaccharides.

Enantioselective Total Synthesis of Nigelladine A via Late-Stage C-H Oxidation Enabled by an Engineered P450 Enzyme

An enantioselective total synthesis of the norditerpenoid alkaloid nigelladine A is described. Strategically, the synthesis relies on a late-stage C-H oxidation of an advanced intermediate. While traditional chemical methods failed to deliver the desired outcome, an engineered cytochrome P450 enzyme was employed to effect a chemo- and regioselective allylic C-H oxidation in the presence of four oxidizable positions. The enzyme variant was readily identified from a focused library of three enzymes, allowing for completion of the synthesis without the need for extensive screening.

Exploring the transferase activity of Ffase from Schwanniomyces occidentalis, a β-fructofuranosidase showing high fructosyl-acceptor promiscuity

The β-fructofuranosidase from the yeast Schwanniomyces occidentalis (Ffase) produces the prebiotic sugars 6-kestose and 1-kestose by transfructosylation of sucrose, which makes it of biotechnological interest. In this study, the hydrolase and transferase activity of this enzyme was kinetically characterized and its potential to synthesize new fructosylated products explored. A total of 40 hydroxylated compounds were used as potential fructosyl-acceptor alternatives to sucrose. Only 17 of them, including some monosaccharides, disaccharides, and oligosaccharides as well as alditols and glycosides were fructosylated. The best alternative acceptors were the alditols. The major transfer product of the reaction including mannitol was purified and characterized as 1-O-β-D-fructofuranosyl-D-mannitol, whose maximum concentration reached 44 g/L, representing about 7.3 % of total compounds in the mixture and 89 % of all products generated by transfructosylation. The reactions including erythritol produced 35 g/L of an isomer mixture comprising 1- and 4-O-β-D-fructofuranosyl-D-erythritol. In addition, Ffase produced 24 g/L of the disaccharide blastose by direct fructosylation of glucose, which makes it the first enzyme characterized from yeast showing this ability. Thus, novel fructosylated compounds with potential applications in food and pharmaceutical industries can be obtained due to the Ffase fructosyl-acceptor promiscuity.