159 research outputs found
Physiological effects, biosynthesis, and derivatization of key human milk tetrasaccharides, lacto-N-tetraose, and lacto-N-neotetraose
No full textHuman milk oligosaccharides (HMOs) have recently attracted ever-increasing interest because of their versatile physiological functions. In HMOs, two tetrasaccharides, lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT), constitute the essential components, each accounting 6% (w/w) of total HMOs. Also, they serve as core structures for fucosylation and sialylation, generating functional derivatives and elongation generating longer chains of core structures. LNT, LNnT, and their fucosylated and/or sialylated derivatives account for more than 30% (w/w) of total HMOs. For derivatization, LNT and LNnT can be modified into a series of complex fucosylated and/or sialylated HMOs by transferring fucose residues at α1,2-, α1,3-, and α1,3/4-linkage and/or sialic acid residues at α2,3- and α2,6-linkage. Such structural diversity allows these HMOs to possess great commercial value and an application potential in the food and pharmaceutical industries. In this review, we first elaborate the physiological functions of these tetrasaccharides and derivatives. Next, we extensively review recent developments in the biosynthesis of LNT, LNnT, and their derivatives in vitro and in vivo by employing advanced enzymatic reaction systems and metabolic engineering strategies. Finally, future perspectives in the synthesis of these HMOs using enzymatic and metabolic engineering approaches are presented.
Development and Classification of Functional Carbohydrate Processing Enzymes in the Food Industry
No full textImproving the catalytic behaviors of Lactobacillus-derived fructansucrases by truncation strategies
No full textFructansucrases (FSs), including inulosucrase (IS) and levansucrase (LS), are the members of the Glycoside Hydrolase family 68 (GH68) enzymes. IS and LS catalyze the polymerization of the fructosyl moiety from sucrose to inulin- and levan-type fructans, respectively. Lactobacillus-derived FSs have relatively extended N- and Cterminal sequences. However, the functional roles of these sequences in their enzymatic properties and fructan biosynthesis remain largely unknown. Limosilactobacillus reuteri (basionym: Lactobacillus reuteri) 121 could produce both IS and LS, abbreviated as Lare121-IS and Lare121-LS, respectively. In this study, it was found that the terminal truncation displayed an obvious effect on their activities and the N-terminal truncated variants, Lare121-IS Delta 177-701 and Lare121-LS Delta 154-686, displayed the highest activities. Melting temperature (Tm) and the thermostability at 50 degrees C were measured to evaluate the stability of various truncated versions, revealing the different effects of N-terminal on the stability. The average molecular weight and polymerization degree of the fructans produced by different truncated variants did not change considerably, indicating that N-terminal truncation had low influence on fructan biosynthesis. In addition, it was found that N-terminal truncation could also improve the activity of other reported FSs from Lactobacillus species
Improving the Thermostability and Catalytic Activity of an Inulosucrase by Rational Engineering for the Biosynthesis of Microbial Inulin
No full textThermostability and enzymatic activity are two vital indexes determining the application of an enzyme on an industrial scale. A truncated inulosucrase, Laga-IS Delta 138-702, from Lactobacillus gasseri showed high catalysis activity. To further enhance its thermostability and activity, multiple sequence alignment (MSA) and rational design based on the modeled structure were performed. Variants A446E, S482A, I614M, and A627S were identified with an improved denaturation temperature (T-m) of more than 1 degrees C. A combinational mutation method was further carried out to explore the synergistic promotion effects of singlepoint mutants. Additionally, 33 residues at the N-terminus were truncated to construct mutant M4(N-33). The half-life of M4(N-33) at 55 degrees C increased by 120 times compared to that of Laga-IS Delta 138-702, and the relative activity of M4(N-33) increased up to 152% at the optimal pH and temperature (pH 5.5 and 60 degrees C). Molecular dynamics (MD) simulations illustrated the decreased b-factor of the surface loop of M4(N-33)
Inulosucrase, an Efficient Transfructosylation Tool for the Synthesis of Microbial Inulin
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