Bottom-Up Synthesized Glucan Materials: Opportunities from Applied Biocatalysis

Linear d-glucans are natural polysaccharides of simple chemical structure. They are comprised of d-glucosyl units linked by a single type of glycosidic bond. Noncovalent interactions within, and between, the d-glucan chains give rise to a broad variety of macromolecular nanostructures that can assemble into crystalline-organized materials of tunable morphology. Structure design and functionalization of d-glucans for diverse material applications largely relies on top-down processing and chemical derivatization of naturally derived starting materials. The top-down approach encounters critical limitations in efficiency, selectivity, and flexibility. Bottom-up approaches of d-glucan synthesis offer different, and often more precise, ways of polymer structure control and provide means of functional diversification widely inaccessible to top-down routes of polysaccharide material processing. Here the natural and engineered enzymes (glycosyltransferases, glycoside hydrolases and phosphorylases, glycosynthases) for d-glucan polymerization are described and the use of applied biocatalysis for the bottom-up assembly of specific d-glucan structures is shown. Advanced material applications of the resulting polymeric products are further shown and their important role in the development of sustainable macromolecular materials in a bio-based circular economy is discussed.

Enzymatic Synthesis of α-Glucan Microparticles Using Amylosucrases from Bifidobacterium Species and Its Physicochemical Properties

α-Glucan microparticles (GMPs) have significant potential as high-value biomaterials in various industries. This study proposes a bottom-up approach for producing GMPs using four amylosucrases from Bifidobacterium sp. (BASs). The physicochemical characteristics of these GMPs were analyzed, and the results showed that the properties of the GMPs varied depending on the type of enzymes used in their synthesis. As common properties, all GMPs exhibited typical B-type crystal patterns and poor colloidal dispersion stability. Interestingly, differences in the physicochemical properties of GMPs were generated depending on the synthesis rate of linear α-glucan by the enzymes and the degree of polymerization (DP) distribution. Consequently, we found differences in the properties of GMPs depending on the DP distribution of linear glucans prepared with four BASs. Furthermore, we suggest that precise control of the type and characteristics of the enzymes provides the possibility of producing GMPs with tailored physicochemical properties for various industrial applications.

Short-chain glucan self-assembly for green synthesis of functional biomaterials: Mechanism, synthesis, and microstructural control

Short-chain glucan (SCG) is a linear homopolymer containing 10 to 50 glucose units linked with α(1,4) glycosidic bonds. With its abundant, low-cost, nontoxic, biodegradable/biocompatible nature, self-assembled SCG particles (SSC) have emerged as functional biomaterials, which have recently attracted tremendous attentions in various fields. SCG self-assembly occurs through the spontaneous association of molecules under equilibrium conditions into stable and structurally well-defined nanoscale or micrometer-scale aggregates, which is governed by various intermolecular non-covalent interactions, including hydrogen-bonding, electrostatic, hydrophobic, and van der Waals. With precise and effective control of the self-assembly process of SSC, its structural modulation and function integration can be expected. Thus, we convinced that SCG self-assembly could provide an effective means of developing starch-based functional biomaterials with beneficial health properties and wide application in food industries. In this review, we provide an overview of recent advances in the green approach for the self-assembly of SSC, as well as the influence of thermodynamic and kinetic factors on its morphology and physicochemical properties. We highlight recent contributions to developing strategies for the construction of SSC with increasing complexity and functionality that are suitable for a variety of food applications. Finally, we briefly outline our perspectives and discuss the challenges in the field.

Starch-Coated Magnetic Iron Oxide Nanoparticles for Affinity Purification of Recombinant Proteins

Starch-coated magnetic iron oxide nanoparticles have been synthesized by a simple, fast, and cost-effective co-precipitation method with cornstarch as a stabilizing agent. The structural and magnetic characteristics of the synthesized material have been studied by transmission electron microscopy, Mössbauer spectroscopy, and vibrating sample magnetometry. The nature of bonds between ferrihydrite nanoparticles and a starch shell has been examined by Fourier transform infrared spectroscopy. The data on the magnetic response of the prepared composite particles have been obtained by magnetic measurements. The determined magnetic characteristics make the synthesized material a good candidate for use in magnetic separation. Starch-coated magnetic iron oxide nanoparticles have been tested as an affinity sorbent for one-step purification of several recombinant proteins (cardiac troponin I, survivin, and melanoma inhibitory activity protein) bearing the maltose-binding protein as an auxiliary fragment. It has been shown that, due to the highly specific binding of this fragment to the starch shell, the target fusion protein is selectively immobilized on magnetic nanoparticles and eluted with the maltose solution. The excellent efficiency of column-free purification, high binding capacity of the sorbent (100–500 µg of a recombinant protein per milligram of starch-coated magnetic iron oxide nanoparticles), and reusability of the obtained material have been demonstrated.

Comparative study on four amylosucrases from Bifidobacterium species

Amylosucrase (ASase) is α-glucan-producing enzyme. Four putative ASase genes (bdas, blas, bpas, and btas) were cloned from Bifidobacterium sp. and expressed in Escherichia coli. All ASases from Bifidobacterium sp. (BAS) displayed typical ASase properties with slightly different characteristics. Among the BASs studied, BdAS and BpAS showed maximal enzyme activities at 35 and 30 °C, respectively, whereas BlAS and BtAS were maximally active at higher temperatures, i.e., 45 and 50 °C, respectively. BpAS exhibited optimum pH under slightly basic conditions (pH 8.0), while BdAS, BlAS, and BtAS preferred weakly acidic conditions (pH 5.0-6.0). All BASs showed higher isomerization activities. Particularly, BlAS produced more trehalulose than turanose. Although polymerization was the highest for BtAS, BtAS synthesized α-1, 4-glucans with a lower degree of polymerization than that of the other BASs. The versatile properties of the BASs described could contribute to the efficient production of highly valuable biomaterials for the agriculture, food, and pharmaceutical industries.

Detection of Escherichia coli O157:H7 Using Automated Immunomagnetic Separation and Enzyme-Based Colorimetric Assay

The food industry requires rapid and simple detection methods for preventing harm from pathogenic bacteria. Until now, various technologies used to detect foodborne bacteria were time-consuming and laborious. Therefore, we have developed an automated immunomagnetic separation combined with a colorimetric assay for the rapid detection of E. coli O157:H7 in food samples. The colorimetric detection method using enzymatic reaction is fascinating because of its simplicity and rapidity and does not need sophisticated devices. Moreover, the proposed procedures for the detection of bacteria in food take less than 3 h including pre-enrichment, separation and detection steps. First, target-specific immunomagnetic beads were introduced to contaminated milk in a pre-enrichment step. Second, the pre-enriched sample solution containing target bacteria bound on immunomagnetic beads was injected into an automated pretreatment system. Subsequently, the immunomagnetic beads along with target bacteria were separated and concentrated into a recovery tube. Finally, released β-galactosidase from E. coli O157:H7 after lysis was reacted with chlorophenol red β-galactopyranoside (CPRG) used as a substrate and the colorimetric change of CPRG was determined by absorbance measuring or the naked eye. By the proposed approach in this study, we could detect 3 × 10² CFU/mL of E. coli O157:H7 from a milk sample within 3 h.

Versatile biotechnological applications of amylosucrase, a novel glucosyltransferase

Amylosucrase (AS; EC 2.4.1.4) is an enzyme that has great potential in the biotechnology and food industries, due to its multifunctional enzyme activities. It can synthesize α-1,4-glucans, like amylose, from sucrose as a sole substrate, but importantly, it can also utilize various other molecules as acceptors. In addition, AS produces sucrose isomers such as turanose and trehalulose. It also efficiently synthesizes modified starch with increased ratios of slow digestive starch and resistant starch, and glucosylated functional compounds with increased water solubility and stability. Furthermore, AS produces turnaose more efficiently than other carbohydrate-active enzymes. Amylose synthesized by AS forms microparticles and these can be utilized as biocompatible materials with various bio-applications, including drug delivery, chromatography, and bioanalytical sciences. This review not only compares the gene and enzyme characteristics of microbial AS, studied to date, but also focuses on the applications of AS in the biotechnology and food industries.

Effect of Lecithin on the Spontaneous Crystallization of Enzymatically Synthesized Short-Chain Amylose Molecules into Spherical Microparticles

Here, we report a facile and effective one-pot approach to prepare uniform amylose-based polymeric microparticles (PMPs) through enzymatic synthesis of short-chain amylose (SCA) followed by spontaneous self-assembly of the SCA in the presence of lecithin. The effect of lecithin on nucleation and growth kinetics of amylose microparticles was investigated by monitoring the turbidity of reaction solution and the size of particles over the course of the self-assembly process. The results suggest that lecithin played a critical role in controlling the self-assembly kinetics to form uniform amylose microparticles through steric stabilization of the growing particles and diffusion-limited growth effect. The crystallinity of amylose microparticles was not affected by lecithin, implying that lecithin did not disrupt the crystal structure within the particle and would mainly be present on the surface of the microparticles. Considering its biodegradable and biocompatible nature, the amylose-based microparticles would find a range of useful applications in the area of food, cosmetics, medicine, chromatography and other related materials sciences.

Molecular Rearrangement of Glucans from Natural Starch To Form Size-Controlled Functional Magnetic Polymer Beads

Herein, we report a fairly simple and environmentally friendly approach for the fabrication of starch-based magnetic polymer beads (SMPBs) with uniform shape and size through spontaneous rearrangement of short-chain glucan (SCG) produced by enzymatic debranching of waxy maize starch. The paramagnetic materials, dextran-coated iron oxide nanoparticles (Dex@IONPs), were readily incorporated into the starch microstructure and rendered a superparamagnetic property to the SMPBs. The morphology and size of resulting SMPBs turned out to be modulated by Dex@IONPs in a concentration-dependent manner, of which Dex@IONPs was assumed to be acting as a seed inducing the epitaxial crystallization of SCG and further transforming it into homogeneous microparticles. The surface of SMPBs was readily functionalized with an antibody through a one-step reaction using a linker protein. The immuno-SMPBs showed great capture efficiency (>90%) for target bacteria. The colloidal stability and favorable surface environment for biomolecules are believed to be responsible for the high capture efficiency and specificity of the SMPBs. Furthermore, the captured bacteria along with antibody and linker protein were effectively eluted from the surface of SMPBs by adding free maltose, making this new material suitable for various chromatographic applications.

Amylosucrase as a transglucosylation tool: From molecular features to bioengineering applications

Amylosucrase (EC 2.4.1.4, ASase), an outstanding sucrose-utilizing transglucosylase in the glycoside hydrolase family 13, can produce glucans with only α-1,4 linkages. Generally, on account of a double-displacement mechanism, ASase can catalyze polymerization, isomerization, and hydrolysis reactions with sucrose as the sole substrate, and has transglycosylation capacity to attach glucose molecules from sucrose to extra glycosyl acceptors. Based on extensive enzymology research, this review presents the characteristics of various ASases, including their microbial metabolism, preparation, and enzymatic properties, and exhibits structure-based strategies in the improvement of activity, specificity, and thermostability. As a vital transglucosylation tool of producing sugars, carbohydrate-based bioactive compounds, and materials, the bioengineering applications of ASases are also systematically summarized.

Identification of an α-(1,4)-Glucan-Synthesizing Amylosucrase from Cellulomonas carboniz T26

Amylosucrase, catalyzing the synthesis of α-(1,4)-glucan from sucrose, has been widely studied and used in carbohydrate biotransformation because of its versatile activities. In this study, a novel amylosucrase was characterized from Cellulomonas carboniz T26. The recombinant enzyme was overexpressed in Escherchia coli and purified by nickel affinity chromatography. It was determined to be a monomeric protein with a molecular mass of 72 kDa. The optimum pH and temperature for transglucosylation were measured to be pH 7.0 and 40 °C. The transglucosylation activity was significantly higher than the hydrolytic activity. The main product generated from sucrose was structurally determined to be α-(1,4)-glucan. A small amount of glucose was produced by hydrolysis, and sucrose isomers including turanose and trehalulose were generated as minor products. The ratio of hydrolytic, polymerization, and isomerization reactions was calculated to be 5.8:84.0:10.2. The enzyme favored production of long-chain insoluble α-glucan at lower temperature.

Enzymes as Green Catalysts for Precision Macromolecular Synthesis

The present article comprehensively reviews the macromolecular synthesis using enzymes as catalysts. Among the six main classes of enzymes, the three classes, oxidoreductases, transferases, and hydrolases, have been employed as catalysts for the in vitro macromolecular synthesis and modification reactions. Appropriate design of reaction including monomer and enzyme catalyst produces macromolecules with precisely controlled structure, similarly as in vivo enzymatic reactions. The reaction controls the product structure with respect to substrate selectivity, chemo-selectivity, regio-selectivity, stereoselectivity, and choro-selectivity. Oxidoreductases catalyze various oxidation polymerizations of aromatic compounds as well as vinyl polymerizations. Transferases are effective catalysts for producing polysaccharide having a variety of structure and polyesters. Hydrolases catalyzing the bond-cleaving of macromolecules in vivo, catalyze the reverse reaction for bond forming in vitro to give various polysaccharides and functionalized polyesters. The enzymatic polymerizations allowed the first in vitro synthesis of natural polysaccharides having complicated structures like cellulose, amylose, xylan, chitin, hyaluronan, and chondroitin. These polymerizations are "green" with several respects; nontoxicity of enzyme, high catalyst efficiency, selective reactions under mild conditions using green solvents and renewable starting materials, and producing minimal byproducts. Thus, the enzymatic polymerization is desirable for the environment and contributes to "green polymer chemistry" for maintaining sustainable society.

Ultrasensitive determination of carcinoembryonic antigens using a magnetoimpedance immunosensor

The schematics of the experimental setup for quantitative and ultrasensitive detection of CEA.