Glycosyl Azides – An Alternative Way to Disaccharides

Rutinosidase and other diglycosidases: Rising stars in biotechnology

Diglycosidases are a special class of glycosidases (EC 3.2.1) that catalyze the separation of intact disaccharide moieties from the aglycone part. The main diglycosidase representatives comprise rutinosidases that cleave rutinose (α-l-Rha-(1-6)-β-d-Glc) from rutin or other rutinosides, and (iso)primeverosidases processing (iso)primeverosides (d-Xyl-(1-6)-β-d-Glc), but other activities are known. Notably, some diglycosidases may be ranked as monoglucosidases with enlarged substrate specificity. Diglycosidases are found in various microorganisms and plants. Diglycosidases are used in the food industry for aroma enhancement and flavor modification. Besides their hydrolytic activity, they also possess pronounced synthetic (transglycosylating) capabilities. Recently, they have been demonstrated to glycosylate various substrates in a high yield, including peculiar species like inorganic azide or carboxylic acids, which is a unique feature in biocatalysis. Rhamnose-containing compounds such as rutinose are currently receiving increased attention due to their proven activity in anti-cancer and dermatological experimental studies. This review demonstrates the vast and yet underrated biotechnological potential of diglycosidases from various sources (plant, microbial), and reveals perspectives on the use of these catalysts as well as of their products in biotechnology.

Flavonoids as Aglycones in Retaining Glycosidase-Catalyzed Reactions: Prospects for Green Chemistry

Flavonoids and their glycosides are abundant in many plant-based foods. The (de)glycosylation of flavonoids by retaining glycoside hydrolases has recently attracted much interest in basic and applied research, including the possibility of altering the glycosylation pattern of flavonoids. Research in this area is driven by significant differences in physicochemical, organoleptic, and bioactive properties between flavonoid aglycones and their glycosylated counterparts. While many flavonoid glycosides are present in nature at low levels, some occur in substantial quantities, making them readily available low-cost glycosyl donors for transglycosylations. Retaining glycosidases can be used to synthesize natural and novel glycosides, which serve as standards for bioactivity experiments and analyses, using flavonoid glycosides as glycosyl donors. Engineered glycosidases also prove valuable for the synthesis of flavonoid glycosides using chemically synthesized activated glycosyl donors. This review outlines the bioactivities of flavonoids and their glycosides and highlights the applications of retaining glycosidases in the context of flavonoid glycosides, acting as substrates, products, or glycosyl donors in deglycosylation or transglycosylation reactions.

Engineered Regulon to Enable Autonomous Azide Ion Biosensing, Recombinant Protein Production, and in Vivo Glycoengineering

Detection of azide-tagged biomolecules (e.g., azido sugars) inside living cells using "click" chemistry has been revolutionary to the field of chemical biology. However, we currently still lack suitable synthetic biology tools to autonomously and rapidly detect azide ions. Here, we have developed an engineered synthetic promoter system called cyn regulon, and complementary Escherichia coli engineered strains, to selectively detect azide ions and autonomously induce downstream expression of reporter genes. The engineered cyn azide operon allowed highly tunable reporter green fluorescent protein (GFP) expression over three orders of inducer azide ion concentrations (0.01-5 mM) and rapidly induced GFP expression by over 600-fold compared to the uninduced control. Next, we showcase the superior performance of this engineered cyn-operon over the classical lac-operon for recombinant protein production. Finally, we highlight how this synthetic biology toolkit can enable glycoengineering-based applications by facilitating in vivo activity screening of mutant carbohydrate-active enzymes (CAZymes), called glycosynthases, using azido sugars as donor substrates.

Biocompatible glyconanomaterials based on HPMA-copolymer for specific targeting of galectin-3

Background

Galectin-3 (Gal-3) is a promising target in cancer therapy with a high therapeutic potential due to its abundant localization within the tumor tissue and its involvement in tumor development and proliferation. Potential clinical application of Gal-3-targeted inhibitors is often complicated by their insufficient selectivity or low biocompatibility. Nanomaterials based on N-(2-hydroxypropyl)methacrylamide (HPMA) nanocarrier are attractive for in vivo application due to their good water solubility and lack of toxicity and immunogenicity. Their conjugation with tailored carbohydrate ligands can yield specific glyconanomaterials applicable for targeting biomedicinally relevant lectins like Gal-3.

Results

In the present study we describe the synthesis and the structure-affinity relationship study of novel Gal-3-targeted glyconanomaterials, based on hydrophilic HPMA nanocarriers. HPMA nanocarriers decorated with varying amounts of Gal-3 specific epitope GalNAcβ1,4GlcNAc (LacdiNAc) were analyzed in a competitive ELISA-type assay and their binding kinetics was described by surface plasmon resonance. We showed the impact of various linker types and epitope distribution on the binding affinity to Gal-3. The synthesis of specific functionalized LacdiNAc epitopes was accomplished under the catalysis by mutant β-N-acetylhexosaminidases. The glycans were conjugated to statistic HPMA copolymer precursors through diverse linkers in a defined pattern and density using Cu(I)-catalyzed azide–alkyne cycloaddition. The resulting water-soluble and structurally flexible synthetic glyconanomaterials exhibited affinity to Gal-3 in low μM range.

Conclusions

The results of this study reveal the relation between the linker structure, glycan distribution and the affinity of the glycopolymer nanomaterial to Gal-3. They pave the way to specific biomedicinal glyconanomaterials that target Gal-3 as a therapeutic goal in cancerogenesis and other disorders.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0399-1) contains supplementary material, which is available to authorized users.

Insights into Penicillium brasilianum Secondary Metabolism and Its Biotechnological Potential

Over the past few years Penicillium brasilianum has been isolated from many different environmental sources as soil isolates, plant endophytes and onion pathogen. All investigated strains share a great ability to produce bioactive secondary metabolites. Different authors have investigated this great capability and here we summarize the metabolic potential and the biological activities related to P. brasilianum’s metabolites with diverse structures. They include secondary metabolites of an alkaloid nature, i.e., 2,5-diketopiperazines, cyclodepsipeptides, meroterpenoids and polyketides. Penicillium brasilianum is also described as a great source of enzymes with biotechnological application potential, which is also highlighted in this review. Additionally, this review will focus on several aspects of Penicillium brasilianum and interesting genomic insights.

On the phosphorylase activity of GH3 enzymes: A β-N-acetylglucosaminidase from Herbaspirillum seropedicae SmR1 and a glucosidase from Saccharopolyspora erythraea

A phosphorolytic activity has been reported for beta-N-acetylglucosaminidases from glycoside hydrolase family 3 (GH3) giving an interesting explanation for an unusual histidine as catalytic acid/base residue and suggesting that members from this family may be phosphorylases [J. Biol. Chem. 2015, 290, 4887]. Here, we describe the characterization of Hsero1941, a GH3 beta-N-acetylglucosaminidase from the endophytic nitrogen-fixing bacterium Herbaspirillum seropedicae SmR1. The enzyme has significantly higher activity against pNP-beta-D-GlcNAcp (K_m = 0.24 mM, k_cat = 1.2 s^-1, k_cat/K_m = 5.0 mM^-1s^-1) than pNP-beta-D-Glcp (K_m = 33 mM, k_cat = 3.3 × 10^-3 s^-1, k_cat/K_m = 9 × 10^-4 mM^-1s^-1). The presence of phosphate failed to significantly modify the kinetic parameters of the reaction. The enzyme showed a broad aglycone site specificity, being able to hydrolyze sugar phosphates beta-D-GlcNAc 1P and beta-D-Glc 1P, albeit at a fraction of the rate of hydrolysis of aryl glycosides. GH3 beta-glucosidase EryBI, that does not have a histidine as the general acid/base residue, also hydrolyzed beta-D-Glc 1P, at comparable rates to Hsero1941. These data indicate that Hsero1941 functions primarily as a hydrolase and that phosphorolytic activity is likely adventitious. The prevalence of histidine as a general acid/base residue is not predictive, nor correlative, with GH3 beta-N-acetylglucosaminidases having phosphorolytic activity.

Enzymatic glycosylation of small molecules: challenging substrates require tailored catalysts

Glycosylation can significantly improve the physicochemical and biological properties of small molecules like vitamins, antibiotics, flavors, and fragrances. The chemical synthesis of glycosides is, however, far from trivial and involves multistep routes that generate lots of waste. In this review, biocatalytic alternatives are presented that offer both stricter specificities and higher yields. The advantages and disadvantages of different enzyme classes are discussed and illustrated with a number of recent examples. Progress in the field of enzyme engineering and screening are expected to result in new applications of biocatalytic glycosylation reactions in various industrial sectors.

Carbohydrate synthesis and biosynthesis technologies for cracking of the glycan code: recent advances

The glycan code of glycoproteins can be conceptually defined at molecular level by the sequence of well characterized glycans attached to evolutionarily predetermined amino acids along the polypeptide chain. Functional consequences of protein glycosylation are numerous, and include a hierarchy of properties from general physicochemical characteristics such as solubility, stability and protection of the polypeptide from the environment up to specific glycan interactions. Definition of the glycan code for glycoproteins has been so far hampered by the lack of chemically defined glycoprotein glycoforms that proved to be extremely difficult to purify from natural sources, and the total chemical synthesis of which has been hitherto possible only for very small molecular species. This review summarizes the recent progress in chemical and chemoenzymatic synthesis of complex glycans and their protein conjugates. Progress in our understanding of the ways in which a particular glycoprotein glycoform gives rise to a unique set of functional properties is now having far reaching implications for the biotechnology of important glycodrugs such as therapeutical monoclonal antibodies, glycoprotein hormones, carbohydrate conjugates used for vaccination and other practically important protein-carbohydrate conjugates.

Heterologous expression and characterization of an N-acetyl-β-D-hexosaminidase from Lactococcus lactis ssp. lactis IL1403

The lnbA gene of Lactococcus lactis ssp. lactis IL1403 encodes a polypeptide with similarity to lacto-N-biosidases and N-acetyl-β-D-hexosaminidases. The gene was cloned into the expression vector pET-21d and overexpressed in Escherichia coli BL21* (DE3). The recombinant purified enzyme (LnbA) was a monomer with a molecular weight of approximately 37 kDa. Studies with chromogenic substrates including p-nitrophenyl N-acetyl-β-D-glucosamine (pNP-GlcNAc) and p-nitrophenyl N-acetyl-β-D-galactosamine (pNP-GalNAc) showed that the enzyme had both N-acetyl-β-D-glucosaminidase and N-acetyl-β-D-galactosaminidase activity, thus indicating that the enzyme is an N-acetyl-β-D-hexosaminidase. K(m) and k(cat) for pNP-GlcNAc were 2.56 mM and 26.7 s(-1), respectively, whereas kinetic parameters for pNP-GalNAc could not be determined due to the K(m) being very high (>10 mM). The optimal temperature and pH of the enzyme were 37 °C and 5.5, respectively, for both substrates. The half-life of activity at 37 °C and pH 6.0 was 53 h, but activity was completely abolished after 30 min at 50 °C, meaning that the enzyme has relatively low temperature stability. The enzyme was stable in the pH 5.5-8 range and was unstable at pH below 5.5. Studies with natural substrates showed hydrolytic activity on chito-oligosaccharides but not on colloidal chitin or chitosan. Transglycosylation products were not detected. In all, the data suggest that LnbA's role may be to degrade chito-oligosaccharides that are produced by the previously described chitinolytic system of L. lactis.

Alpha-mannosidases from the digestive fluid of Rhynchophorus Palmarum larvae as novel biocatalysts for transmannosylation reactions

Two biological fluids, namely hemolymph and digestive fluid from the larval stage of Rhynchophorus palmarum Linneaus, a serious pest in agroecosystem exploiting oil palm, were screened for hydrolytic activities, by the use of synthetic and natural glycoside substrates. Several exo and endoglycosidase activities were observed but, the interesting alpha-mannosidase activity (0.41 +/- 0.04 UI) had attracted our attention. So, we have previously demonstrated that this activity harbours four distinctive alpha-mannosidase isoforms named RpltM, RplM1, RplM2 and RplM3. We have extended this work to determine the ability of these enzymes to catalyze synthesis reactions. Finally, we have revealed that, alpha-mannosidases from the digestive fluid of R. palmarum larvae catalyze transmannosylation reactions. The stability of the enzymes and the optimization of the transfer product yield were studied as functions of pH, enzyme unit, starting concentration of donor or acceptor and time. It was shown that, in experimental optimum conditions, average yields of 12.34 +/- 0.75, 12.15 +/- 0.79, 5.59 +/- 0.35 and 8.43 +/- 0.50% were obtained for the alpha-mannosidases RpltM, RplM1, RplM2 and RplM3, respectively. On the basis of this work, alpha-mannosidases from the digestive fluid of Rhynchophorus palmarum larvae appear to be a valuable tool for the preparation of neoglycoconjugates.

Glycosidases: a key to tailored carbohydrates

In recent years, carbohydrate-processing enzymes have become the enzymes of choice in many applications thanks to their stereoselectivity and efficiency. This review presents recent developments in glycosidase-catalyzed synthesis via two complementary approaches: the use of wild-type enzymes with engineered substrates, and mutant glycosidases. Genetic engineering has recently produced glucuronyl synthases, an inverting xylosynthase and the first mutant endo-beta-N-acetylglucosaminidase. A thorough selection of enzyme strains and aptly modified substrates have resulted in rare glycostructures, such as N-acetyl-beta-galactosaminuronates, beta1,4-linked mannosides and alpha1,4-linked galactosides. The efficient selection of mutant enzymes is facilitated by high-throughput screening assays involving the co-expression of coupled enzymes or chemical complementation. Selective glycosidase inhibitors and highly specific glycosidases are finding attractive applications in biomedicine, biology and proteomics.