Glycans in regeneration

Advances in protein glycosylation and its role in tissue repair and regeneration

After tissue damage, a series of molecular and cellular events are initiated to promote tissue repair and regeneration to restore its original structure and function. These events include inter-cell communication, cell proliferation, cell migration, extracellular matrix differentiation, and other critical biological processes. Glycosylation is the crucial conservative and universal post-translational modification in all eukaryotic cells [1], with influential roles in intercellular recognition, regulation, signaling, immune response, cellular transformation, and disease development. Studies have shown that abnormally glycosylation of proteins is a well-recognized feature of cancer cells, and specific glycan structures are considered markers of tumor development. There are many studies on gene expression and regulation during tissue repair and regeneration. Still, there needs to be more knowledge of complex carbohydrates' effects on tissue repair and regeneration, such as glycosylation. Here, we present a review of studies investigating protein glycosylation in the tissue repair and regeneration process.

Exploring the Candidate Terminal Glycan Profile in Neural Regeneration of the Sea Urchin Paracentrotus lividus, Using Lectin Blotting and Mass Spectrometry

Glycans are expressed as conjugates of glycoproteins, glycolipids, and proteoglycans. The huge diversity of glycans on glycoconjugates contributes to many biological processes, from glycan-based molecular recognition to developmental events, such as regeneration in the nervous system. Echinoderms, which have a close phylogenetic relationship with chordates, are an important group of marine invertebrates for body regeneration. Although many major roles of glycans on glycoconjugates are known, their role in the glycosylation profile of the nervous system in sea urchins is poorly understood. In this study, we aimed to determine the terminal glycan profile by lectin blotting and to quantify sialic acids by the capillary liquid chromatography electrospray ionization tandem mass spectrometry system in the nervous tissue of the sea urchin Paracentrotus lividus. We determined the N-acetyl-D-glucosamine, mannose, and sialic acids (mainly α2,3 linked) by lectin blotting and five types of sialic acids (N-glycolylneuraminic acid, N-acetylneuraminic acid, 9-O-acetyl-N-alycolylneuraminic acid, 5-N-acetyl-9-O-acetyl-N-acetylneuraminic acid, and di-O-acetylated-N-alycolylneuraminic acid) by capillary liquid chromatography electrospray ionization tandem mass spectrometry. This potential first description of the terminal glycan profile in the nervous system of the sea urchin is expected to help us understand its role in nervous system development and regeneration.

Engineering the Sialome

The surface of every eukaryotic cell is coated in a dense layer of structurally diverse glycans that together comprise the glycocalyx, a key interface between intracellular biochemistry and the external environment. Many of the glycans within the glycocalyx terminate in anionic monosaccharides belonging to the sialic acid family. Advances in our understanding of the biological processes mediated by sialic acids at the interfaces between cells have catalyzed interest in metabolic, enzymatic, and chemical strategies to edit the total complement of cellular sialic acids-the sialome. Here, we review strategies for altering the composition of the sialome with particular focus on glycan structures and state-of-the-art tools.

NMR analysis and molecular dynamics conformation of α-1,6-linear and α-1,3-branched isomaltose oligomers as mimetics of α-1,6-linked dextran

The conformational preferences of several α-1,6-linear and α-1,3-branched isomalto-oligosaccharides were investigated by NMR and MD-simulations. Right-handed helical structure contributed to the solution geometry in isomaltotriose and isomaltotetraose with one nearly complete helix turn and stabilizing intramolecular hydrogen bonds in the latter by MD-simulation. Decreased helix contribution was observed in α-1,3-glucopyranosyl- and α-1,3-isomaltosyl-branched saccharide chains. Especially the latter modification was predicted to cause a more compact structure consistent with literature rheology measurements as well as with published dextranase-resistant α-1,3-branched oligosaccharides. The findings presented here are significant because they shed further light on the conformational preference of isomalto-oligosaccharides and provide possible help for the design of dextran-based drug delivery systems or for the targeted degradation of capsular polysaccharides by dextranases in multi-drug resistant bacteria.

Structural insights in interactions between RNase from Bacillus Intermedius and rhamnogalacturonan I from potato

Being biocompatible and biodegradable polymers, polysaccharides present a perspective material for drug delivery systems. This study aimed at unraveling the molecular details of interactions between rhamnogalacturonan I, brunched with galactan side chains, and RNase from Bacillus Intermedius, binase. FTIR- and NMR-spectroscopic analyses showed that binase interacts with side chains of the polysaccharide. In complexes with polysaccharide, the protein retains its native structure. The 2D-NMR techniques revealed eight protein residues responsive to polysaccharide binding. Further, computer simulations were carried out to provide the atomistic details of binase-polysaccharide complexes. Both blind and knowledge-based docking procedures elucidate the existence of epitopes on the binase surface with the preferential binding of galactan fragments. The refinement of these complexes by molecular dynamics simulations confirmed stable protein-polysaccharide interactions. The results of this study strengthen the knowledge on non-specific protein-carbohydrate interactions and outline the rhamnogalacturonan I as a possible matrix material for protein delivery systems.

Converting a β-N-acetylhexosaminidase into two trans-β-N-acetylhexosaminidases by domain-targeted mutagenesis

We have recently derived a β-N-acetylhexosaminidase, BbhI, from Bifidobacterium bifidum JCM 1254, which could regioselectively synthesize GlcNAcβ1-3Galβ1-4Glc with a yield of 44.9%. Here, directed evolution of BbhI by domain-targeted mutagenesis was carried out. Firstly, the GH20 domain was selected for random mutagenesis using MEGAWHOP method and a small library of 1300 clones was created. A total of 734 colonies with reduced hydrolytic activity were isolated, and three mutants with elevated transglycosylation yields, GlcNAcβ1-3Galβ1-4Glc yields of 68.5%, 74.7%, and 81.1%, respectively, were obtained. Subsequently, nineteen independent mutants were constructed according to all the mutation sites in these three mutants. After transglycosylation analysis, Asp714 and Trp773 were identified as key residues for improvement in transglycosylation ability and were chosen for the second round of directed evolution by site-saturation mutagenesis. Two most efficient mutants D714T and W773R that acted as trans-β-N-acetylhexosaminidase were finally achieved. D714T with the substitution at the putative nucleophile assistant residue Asp714 by threonine showed high yield of 84.7% with unobserved hydrolysis towards transglycosylation product. W773R with arginine substitution at Trp773 residue locating at the entrance of catalytic cavity led to the yield up to 81.8%. The k_cat/K_m values of D714T and W773R for hydrolysis of pNP-β-GlcNAc displayed drastic decreases. NMR investigation of protein-substrate interaction revealed an invariable mode of the catalytic cavity of D714T, W773R, and WT BbhI. The collective motions of protein model showed the mutations Thr714 and Arg773 exerted little effect on the dynamics of the inside but a large effect on the dynamics of the outside of catalytic cavity.

Polysialic-Acid-Based Micelles Promote Neural Regeneration in Spinal Cord Injury Therapy

Spinal cord injury (SCI) routinely causes the immediate loss and disruption of neurons followed by complicated secondary injuries, including inflammation, oxidative stress, and dense glial scar formation. Inhibitory factors in the lesion scar and poor intrinsic neural regeneration capacity restrict functional recovery after injury. Minocycline, which has neuroprotective activity, can alleviate secondary injury, but the long-term administration of this drug may cause toxicity. Polysialic acid (PSA) is a large cell-surface carbohydrate that is critical for central nervous system development and is capable of promoting precursor cell migration, axon path finding, and synaptic remodeling; thus, PSA plays a vital role in tissue repair and regeneration. Here, we developed a PSA-based minocycline-loaded nanodrug delivery system (PSM) for the synergistic therapy of spinal cord injury. The prepared PSM exerted marked anti-inflammatory and neuroprotective activities both in vitro and in vivo. The administration of PSM could significantly protect neurons and myelin sheaths from damage, reduce the formation of glial scar, recruit endogenous neural stem cells to the lesion site, and promote the regeneration of neurons and the extension of long axons throughout the glial scar, thereby largely improving the locomotor function of SCI rats and exerting a superior therapeutic effect. The findings might provide a novel strategy for SCI synergistic therapy and the utilization of PSA in other central nervous system diseases.

Leveraging advances in biology to design biomaterials

Biomaterials have dramatically increased in functionality and complexity, allowing unprecedented control over the cells that interact with them. From these engineering advances arises the prospect of improved biomaterial-based therapies, yet practical constraints favour simplicity. Tools from the biology community are enabling high-resolution and high-throughput bioassays that, if incorporated into a biomaterial design framework, could help achieve unprecedented functionality while minimizing the complexity of designs by identifying the most important material parameters and biological outputs. However, to avoid data explosions and to effectively match the information content of an assay with the goal of the experiment, material screens and bioassays must be arranged in specific ways. By borrowing methods to design experiments and workflows from the bioprocess engineering community, we outline a framework for the incorporation of next-generation bioassays into biomaterials design to effectively optimize function while minimizing complexity. This framework can inspire biomaterials designs that maximize functionality and translatability.

Profiling of glycan alterations in regrowing limb tissues of Cynops orientalis

Glycans are known to play important roles in molecular recognition, cell-cell adhesion, molecular trafficking, receptor activation, and signal transduction during development and regeneration. Despite numerous investigations of regenerating salamander limbs, global analysis of the precise variation of glycans during the limb regeneration process has received little attention. Here, we have used lectin microarrays and lectin histochemistry to analyze the alterations and distribution of glycans during the early stages leading to blastema formation during Cynops orientalis limb regeneration in response to limb amputation. Compared with the control group, analysis at several time points (3, 7, and 14 days postamputation) using microarrays containing 37 lectins showed that limb tissues expressed significantly different complements of glycans recognized by 9 different lectins. Postamputation limb tissues showed higher expression of two glycan structures recognized by the lectins STL and LTL and lower expression of seven glycan structures recognized by PHA-E, MAL-I, SNA, UEA-I, PHA-E + L, VVA, and GNA. We also observed significant changes in glycans specifically at 7 days postamputation, including higher binding capacity by WFA, GSL-I, and NPA and lower binding capacity by PNA, HHL, ConA, LCA, GSL-II, and PWM. Next, we validated our lectin microarray data using lectin histochemistry in limb tissues. Glycans recognized by STL and GNA showed similar changes in signal intensity to those found in the lectin microarrays, with STL staining in the cytoplasm and GNA in the cytoplasm and nucleus. Our findings are the first report of significant postamputation changes in glycans in limb tissues and suggest that those glycans perform potentially important functions during the early stages of C. orientalis limb regeneration.

Efficient and Regioselective Synthesis of β-GalNAc/GlcNAc-Lactose by a Bifunctional Transglycosylating β-N-Acetylhexosaminidase from Bifidobacterium bifidum

β-N-Acetylhexosaminidases have attracted interest particularly for oligosaccharide synthesis, but their use remains limited by the rarity of enzyme sources , low efficiency, and relaxed regioselectivity of transglycosylation. In this work, genes of 13 β-N-acetylhexosaminidases, including 5 from Bacteroides fragilis ATCC 25285, 5 from Clostridium perfringens ATCC 13124, and 3 from Bifidobacterium bifidum JCM 1254, were cloned and heterogeneously expressed in Escherichia coli The resulting recombinant enzymes were purified and screened for transglycosylation activity. A β-N-acetylhexosaminidase named BbhI, which belongs to glycoside hydrolase family 20 and was obtained from B. bifidum JCM 1254, possesses the bifunctional property of efficiently transferring both GalNAc and GlcNAc residues through β1-3 linkage to the Gal residue of lactose. The effects of initial substrate concentration, pH, temperature, and reaction time on transglycosylation activities of BbhI were studied in detail. With the use of 10 mM pNP-β-GalNAc or 20 mM pNP-β-GlcNAc as the donor and 400 mM lactose as the acceptor in phosphate buffer (pH 5.8), BbhI synthesized GalNAcβ1-3Galβ1-4Glc and GlcNAcβ1-3Galβ1-4Glc at maximal yields of 55.4% at 45°C and 4 h and 44.9% at 55°C and 1.5 h, respectively. The model docking of BbhI with lactose showed the possible molecular basis of strict regioselectivity of β1-3 linkage in β-N-acetylhexosaminyl lactose synthesis.

IMPORTANCE

Oligosaccharides play a crucial role in many biological events and therefore are promising potential therapeutic agents. However, their use is limited because large-scale production of oligosaccharides is difficult. The chemical synthesis requires multiple protecting group manipulations to control the regio- and stereoselectivity of glycosidic bonds. In comparison, enzymatic synthesis can produce oligosaccharides in one step by using glycosyltransferases and glycosidases. Given the lower price of their glycosyl donor and their broader acceptor specificity, glycosidases are more advantageous than glycosyltransferases for large-scale synthesis. β-N-Acetylhexosaminidases have attracted interest particularly for β-N-acetylhexosaminyl oligosaccharide synthesis, but their application is affected by having few enzyme sources, low efficiency, and relaxed regioselectivity of transglycosylation. In this work, we describe a microbial β-N-acetylhexosaminidase that exhibited strong transglycosylation activity and strict regioselectivity for β-N-acetylhexosaminyl lactose synthesis and thus provides a powerful synthetic tool to obtain biologically important GalNAcβ1-3Lac and GlcNAcβ1-3Lac.

Enzymatic Synthesis of Rhamnose Containing Chemicals by Reverse Hydrolysis

Rhamnose containing chemicals (RCCs) are widely occurred in plants and bacteria and are known to possess important bioactivities. However, few of them were available using the enzymatic synthesis method because of the scarcity of the α-L-rhamnosidases with wide acceptor specificity. In this work, an α-L-rhamnosidase from Alternaria sp. L1 was expressed in Pichia pastroris strain GS115. The recombinant enzyme was purified and used to synthesize novel RCCs through reverse hydrolysis in the presence of rhamnose as donor and mannitol, fructose or esculin as acceptors. The effects of initial substrate concentrations, reaction time, and temperature on RCC yields were investigated in detail when using mannitol as the acceptor. The mannitol derivative achieved a maximal yield of 36.1% by incubation of the enzyme with 0.4 M L-rhamnose and 0.2 M mannitol in pH 6.5 buffers at 55°C for 48 h. In identical conditions except for the initial acceptor concentrations, the maximal yields of fructose and esculin derivatives reached 11.9% and 17.9% respectively. The structures of the three derivatives were identified to be α-L-rhamnopyranosyl-(1→6')-D-mannitol, α-L-rhamnopyranosyl-(1→1')-β-D-fructopyranose, and 6,7-dihydroxycoumarin α-L-rhamnopyranosyl-(1→6')-β-D-glucopyranoside by ESI-MS and NMR spectroscopy. The high glycosylation efficiency as well as the broad acceptor specificity of this enzyme makes it a powerful tool for the synthesis of novel rhamnosyl glycosides.