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Cellulose, the Main Component of Biomass
Published in Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel, Hemicelluloses and Lignin in Biorefineries, 2017
Jean-Luc Wertz, Magali Deleu, Séverine Coppée, Aurore Richel
Models of glucose polymerization have been proposed. In the model with single substrate-binding site, the A domain of cellulose synthases binds the UDP-sugar, and the B domain binds the acceptor molecule, the aspartates (D) in the A and B domains forming a single center for glycosyl transfer.46 Inverting glycosyltransferases, including cellulose synthases, are assumed to use a single displacement mechanism with nucleophilic attack by the acceptor molecule at the anomeric carbon of the donor sugar.49 Such a mechanism is presumed to require a base (aspartate residue) to activate the sugar acceptor for nucleophilic attack by deprotonation. For most enzymes, the reaction also involves additional carboxylate(s) (aspartate residue[s]) to coordinate a divalent metal ion on the phosphate group(s) of the nucleotide (Figure 3.7).
Biomems
Published in Simona Badilescu, Muthukumaran Packirisamy, BioMEMS, 2016
Simona Badilescu, Muthukumaran Packirisamy
Glycosyltransferase and glycosidase are carbohydrate-related enzymes and have been used for oligosaccharide synthesis. Bioactive glycoconjugates are essential for biological reactions such as cell adhesion and migration. Enzymatic oligosaccharide synthesis, including the forward reaction, called hydrolysis, and the reverse reaction, called transglycosylation, can be performed in microfluidics.
Kode Technology – a universal cell surface glycan modification technology
Published in Journal of the Royal Society of New Zealand, 2019
Stephen M. Henry, Nicolai V. Bovin
Traditionally modification of the cells has been done by genetic engineering (Stephan and Irvine 2011). Unfortunately, molecular biology approaches are unsuited for additive glycan modification of cells with the outcomes being unpredictable and poorly controlled. This is because glycosylation is probably the most complex secondary gene event in a cell, and multiple glycosyltransferase enzymes are required to make even simple oligosaccharides, which is complicated by the fact that a single enzyme can be responsible for synthesis of different glycans (degeneracy) and different enzymes can make the same glycan (redundancy) (Oriol et al. 1986). Simply adding (‘knocking-in’) one enzyme is probably insufficient to create a new antigen, and such a modification can radically affect the biosynthetic pathway of many glycoconjugates, thus confound experimental observations. However, molecular biology glycan ‘knock-outs’ (resulting in deletion of a glycan family by removal of a glycosyltransferase) are useful techniques for understanding the absence of glycans, although they may still produce confounding results due to disruption of normal glycan biosynthesis. For instance, knocking-out the αGal-transferase gene, responsible for synthesis of important xeno-transplant linear B antigen (Galili 2015), also causes formation of new antigens as a consequence of up-regulation of other glycosyltransferase genes (Huai et al. 2016).
Cyanobacteria mediated heavy metal removal: a review on mechanism, biosynthesis, and removal capability
Published in Environmental Technology Reviews, 2021
Abdullah Al-Amin, Fahmida Parvin, Joydeep Chakraborty, Yong-Ick Kim
Wild type cyanobacteria may not be an ideal organism for all types of heavy metal ion removal operations. Every species has some limitations in biosorption [47]. To combat all of these challenges, engineered cyanobacteria may be a good alternative for ideal heavy metal removal operations. Genetic modification enhances anionic moiety in cell surface and alteration of chemical compounds for optimum heavy metal ion adsorption in cell surface [38]. Cyanobacterial EPS is highly complex in nature. Though knowledge in EPS biosynthesis is still insufficient, EPS synthesis pathway engineering may provide insights for optimizing EPS production, which may enhance anionic moiety in the cell surface. The following three approaches can genetically modify the EPS: EPS synthesis is carbon and energy-demanding process. Expressing BicA transporter in Synechocystis sp. strain PCC6803, resulted in enhancing CO2 uptake, faster growth of the cell, and increase of EPS production [67]. Another approach to enhance carbon availability is by reducing carbon sink and other competitive pathways, for example, sucrose, glycosylglycocerol, and glycogen. This approach may shift the carbon sink toward polysaccharide production [58].Sufficient sugar nucleotides can induce high EPS production. Performing metabolism engineering enhances the expression level of enzymes (phosphoglucomutase, UDP-glucose pyrophosphorylase, UDP-glucose dehydrogenase, and UDP-galactose-4-epimerase), responsible for supplying nucleotide sugar precursor might enhance EPS production [68].Assemblance of monosaccharide's repeated unit into polysaccharide may be achieved by overexpressing native glycosyltransferase or recombining heterologous glycosyltransferase genes [69]. And these polysaccharides will be transported outside the cell as EPS.
Comparative proteomic analysis revealed the metabolic mechanism of excessive exopolysaccharide synthesis by Bacillus mucilaginosus under CaCO3 addition
Published in Preparative Biochemistry & Biotechnology, 2019
Hongyu Xu, Zhiwen Zhang, Hui Li, Yujie Yan, Jinsong Shi, Zhenghong Xu
Exopolysaccharides are water-soluble polysaccharides that are secreted by special microorganisms outside the cell walls in the growth and metabolism and are easily separated from the cells and secreted into the environment.[1,2] The enzymes involved in the synthesis of extracellular polysaccharides are located at different sites of the microbial cells and can be divided into the following four different types. The first enzyme type is located intracellularly and composed primarily of kinases and mutases. The other typical enzymes are glucokinase, phosphoglucose mutase, and glucose, which produce glucose-6-phosphate under the action of glucokinase. Glucose-1-phosphate is formed by the action of phosphoglucose mutase. Most of the glyconucleotide precursors required for the synthesis of extracellular polysaccharides are derived from glucose-1-phosphate; thus, phosphorylation is important for the synthesis of extracellular polysaccharides.[3] Recent studies highlighted a signaling activity for the exopolysaccharides produced by the Bacillus subtilis eps operon. This polymer is recognized by the extracellular domain of a tyrosine kinase that activates its own synthetic pathway.[4] The second type of enzyme is located intracellularly and includes UDP–glucose pyrophosphorylase (UGP) and various epimerases. UGP catalyzes glucose-1-phosphate as an important precursor for the polysaccharide synthesis of UDP–glucose. Under the action of epimerase, UDP–glucose can produce other sugar nucleotide precursors.[5] The third type of enzyme is mostly located in cell membranes, such as glycosyltransferases. The sugar nucleotides are transported to a glycosyl lipid carrier and then assembled into oligosaccharide repeat units with the participation of a glycosyltransferase.[6] The fourth type of enzyme is located in the cell membrane or extracellularly and presumably associated with bacterial extracellular polysaccharide polymerization. After a macromolecular polysaccharide is produced, it is secreted extracellularly to form a mucin polysaccharide or attached to the surface of the cell to form a capsular polysaccharide.[7]