Transglycosylation reaction of Mucor hiemalis endo-β-N-acetylglucosaminidase using sugar derivatives modified at C-1 or C-2 as oligosaccharide acceptors

Transglycosylation behavior of Mucor hiemalis endo-β-N-acetylglucosaminidase to β-cyclodextrin derivatives with multivalent glucose moieties for synthesizing cyclodextrin-based oligosaccharide clusters

We investigated the transglycosylation reaction of two types of oligosaccharide acceptors, i.e., β-cyclodextrin (CD) derivatives 1 and 2 conjugated with multiple glucose (Glc) units, catalyzed by endo-β-N-acetyl-glucosaminidase from Mucor hiemalis (Endo-M) using the oligosaccharide donor sialoglycopeptide (SGP). The acceptor specificity of the enzyme transglycosylation of 1 and 2 having seven Glc moieties within small nanoscale spatial regions on the β-CDs was investigated on the basis of the effect of the molar ratios of SGP to acceptors 1 or 2 with different spatial configurations on the transglycosylation behavior. The formation of the corresponding CD-based oligosaccharide clusters from Endo-M was also evaluated.

Convergent chemo-enzymatic synthesis of mannosylated glycopeptides; targeting of putative vaccine candidates to antigen presenting cells

The combination of solid phase peptide synthesis and endo-β-N-acetylglucosaminidase (ENGase) catalysed glycosylation is a powerful convergent synthetic method allowing access to glycopeptides bearing full-length N-glycan structures. Mannose-terminated N-glycan oligosaccharides, produced by either total or semi-synthesis, were converted into oxazoline donor substrates. A peptide from the human cytomegalovirus (CMV) tegument protein pp65 that incorporates a well-characterised T cell epitope, containing N-acetylglucosamine at specific Asn residues, was accessed by solid phase peptide synthesis, and used as an acceptor substrate. High-yielding enzymatic glycosylation afforded glycopeptides bearing defined homogeneous high-mannose N-glycan structures. These high-mannose containing glycopeptides were tested for enhanced targeting to human antigen presenting cells (APCs), putatively mediated via the mannose receptor, and for processing by the APCs for presentation to human CD8+ T cells specific for a 9-mer epitope within the peptide. Binding assays showed increased binding of glycopeptides to APCs compared to the non-glycosylated control. Glycopeptides bearing high-mannose N-glycan structures at a single site outside the T cell epitope were processed and presented by the APCs to allow activation of a T cell clone. However, the addition of a second glycan within the T cell epitope resulted in ablation of T cell activation. We conclude that chemo-enzymatic synthesis of mannosylated glycopeptides enhances uptake by human APCs while preserving the immunogenicity of peptide epitopes within the glycopeptides, provided those epitopes are not themselves glycosylated.

Endohexosaminidase-catalyzed synthesis of glycopeptides and proteins

The synthetic application of endohexosaminidase enzymes (e.g., Endo A, Endo M, Endo D) promises to allow ready access to a wide variety of defined homogeneous glycoproteins and glycopeptides. The use ofN-glycan oligosaccharides that are activated at the reducing terminus as oxazolines allows their high-yielding attachment to almost any amino acid, peptide, or protein that contains a GlcNAc residue as an acceptor. A wide variety of oxazoline donors are readily available, either by total synthesis or by isolation of the corresponding oligosaccharide from natural sources and then conversion to the oxazoline in water. The synthetic potential of the enzymes is particularly augmented by the production of mutant glycosynthases, the use of which allows the synthesis of a wide variety of glycopeptides and glycoproteins bearing defined homogeneousN-glycan structures.

Endohexosaminidase-catalysed glycosylation with oxazoline donors: effects of organic co-solvent and pH on reactions catalysed by Endo A and Endo M

The synthetic efficiency of endohexosaminidase-catalysed glycosylation reactions using N-glycan oxazolines as donors was investigated as two reaction parameters were varied. Both the addition of quantities of an organic co-solvent and modulation of reaction pH between 6.5 and 8.0 were found to have different effects on reactions catalysed by either Endo A (and two available mutants) or Endo M, indicating subtle differences between these two family GH85 enzymes. Fine tuning of reaction pH, or the addition of quantities of an organic co-solvent, resulted in beneficial increases in achievable synthetic efficiency by effecting a reduction in the rate of competitive hydrolytic processes.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2003-2004

This review is the third update of the original review, published in 1999, on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings the topic to the end of 2004. Both fundamental studies and applications are covered. The main topics include methodological developments, matrices, fragmentation of carbohydrates and applications to large polymeric carbohydrates from plants, glycans from glycoproteins and those from various glycolipids. Other topics include the use of MALDI MS to study enzymes related to carbohydrate biosynthesis and degradation, its use in industrial processes, particularly biopharmaceuticals and its use to monitor products of chemical synthesis where glycodendrimers and carbohydrate-protein complexes are highlighted.

Introducing N-glycans into natural products through a chemoenzymatic approach

The present study describes an efficient chemoenzymatic method for introducing a core N-glycan of glycoprotein origin into various lipophilic natural products. It was found that the endo-beta-N-acetylglucosaminidase from Arthrobactor protophormiae (Endo-A) had broad substrate specificity and can accommodate a wide range of glucose (Glc)- or N-acetylglucosamine (GlcNAc)-containing natural products as acceptors for transglycosylation, when an N-glycan oxazoline was used as a donor substrate. Using lithocholic acid as a model compound, we have shown that introduction of an N-glycan could be achieved by a two-step approach: chemical glycosylation to introduce a monosaccharide (Glc or GlcNAc) as a handle, and then Endo-A catalyzed transglycosylation to accomplish the site-specific N-glycan attachment. For those natural products that already carry terminal Glc or GlcNAc residues, direct enzymatic transglycosylation using sugar oxazoline as the donor substrate was achievable to introduce an N-glycan. It was also demonstrated that simultaneous double glycosylation could be fulfilled when the natural product contains two Glc residues. This chemoenzymatic method is concise, site-specific, and highly convergent. Because N-glycans of glycoprotein origin can serve as ligands for diverse lectins and cell-surface receptors, introduction of a defined N-glycan into biologically significant natural products may bestow novel properties onto these natural products for drug discovery and development.

Biotechnological aspects of chitinolytic enzymes: a review

Chitin and chitinases (EC 3.2.1.14) have an immense potential. Chitinolytic enzymes have wide-ranging applications such as preparation of pharmaceutically important chitooligosaccharides and N-acetyl D-glucosamine, preparation of single-cell protein, isolation of protoplasts from fungi and yeast, control of pathogenic fungi, treatment of chitinous waste, and control of malaria transmission. In this review, we discuss the occurrence and structure of chitin, the types and sources of chitinases, their mode of action, chitinase production, as well as molecular cloning and protein engineering of chitinases and their biotechnological applications.

Synthesis of mono-glucose-branched cyclodextrins with a high inclusion ability for doxorubicin and their efficient glycosylation using Mucor hiemalis endo-beta-N-acetylglucosaminidase

The mono-glucose-branched cyclodextrins having an appropriate spacer between the beta-cyclodextrin and a glucose moiety were synthesized from beta-cyclodextrin and arbutin. They had the significantly high association constants for doxorubicin, the anticancer agent, in the range of 10(5)-10(6)M(-1), and worked as highly reactive glycosyl acceptors for the transglycosylation reaction by endo-beta-N-acetylglucosaminidase of Mucor hiemalis to produce sialo-complex type oligosaccharide-branched cyclodextrins in the high yields of 65-67%.

Mucor hiemalis endo-β-N-acetylglucosaminidase can transglycosylate a bisecting hybrid-type oligosaccharide from an ovalbumin glycopeptide

We found that the recombinant endo-beta-N-acetylglucosaminidase of Mucor hiemalis (Endo-M) expressed in Candida boidinii had the transglycosylation activity of transferring a bisecting hybrid-type oligosaccharide from an ovalbumin glycopeptide to the acceptor (p-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside) in a good yield of 43%.