An automated platform for the enzyme-mediated assembly of complex oligosaccharides

An automated platform that can synthesize a wide range of complex carbohydrates will greatly increase their accessibility and should facilitate progress in glycoscience. Here we report a fully automated process for enzyme-mediated oligosaccharide synthesis that can give easy access to different classes of complex glycans including poly-N-acetyllactosamine derivatives, human milk oligosaccharides, gangliosides and N-glycans. Our automated platform uses a catch and release approach in which glycosyltransferase-catalysed reactions are performed in solution and product purification is accomplished by solid phase extraction. We developed a sulfonate tag that can easily be installed and enables highly efficient solid phase extraction and product release using a single set of washing conditions, regardless of the complexity of the glycan. Using this custom-built synthesizer, as many as 15 reaction cycles can be performed in an automated fashion without a need for lyophilization or buffer exchange steps

A Biomimetic Synthetic Strategy can Provide Keratan Sulfate I and II Oligosaccharides with Diverse Fucosylation and Sulfation Patterns

Keratan sulfate (KS) is a proteoglycan that is widely expressed in the extracellular matrix of various tissue types where it performs multiple biological functions. KS is the least understood proteoglycan, which in part is due to a lack of panels of well-defined KS oligosaccharides that are needed for structure-binding studies, as analytical standards, to examine substrate specificities of keratinases and for drug development. Here, we report a biomimetic approach that makes it possible to install, in a regioselective manner, sulfates and fucosides on oligo-N-acetyllactosamine (LacNAc) chains to provide any structural element of KS by using specific enzyme modules. It is based on the observation that 1,3-fucosides, 2,6-sialosides and C-6 sulfation of galactose (Gal6S) are mutually exclusive and cannot occur on the same LacNAc moiety. As a result, the pattern of sulfation on galactosides can be controlled by installing1,3-fucosides or 2,6-sialosides to temporarily block certain LacNAc moieties from sulfation by keratan sulfate galactose 6-sulfotransferase (CHST1). The pattern of 1,3-fucosylation and 2,6-sialylation can be controlled by exploiting the mutual exclusivity of these modifications, which in turn controls the sites of sulfation by CHST1. Late-stage treatment with a fucosidase or sialidase to remove blocking fucosides or sialosides provides selectively sulfated KS oligosaccharides. These treatments also unmasked specific galactosides for further controlled modification by CHST1. To showcase the potential of the enzymatic strategy, we have prepared a range of poly-LacNAc derivatives having different patterns of fucosylation and sulfation and several N-glycans decorated by specific arrangements of sulfates

An automated platform for the enzyme-mediated assembly of complex oligosaccharides

An automated platform that can synthesize a wide range of complex carbohydrates will greatly increase their accessibility and should facilitate progress in glycoscience. Here we report a fully automated process for enzyme-mediated oligosaccharide synthesis that can give easy access to different classes of complex glycans including poly-N-acetyllactosamine derivatives, human milk oligosaccharides, gangliosides and N-glycans. Our automated platform uses a catch and release approach in which glycosyltransferase-catalysed reactions are performed in solution and product purification is accomplished by solid phase extraction. We developed a sulfonate tag that can easily be installed and enables highly efficient solid phase extraction and product release using a single set of washing conditions, regardless of the complexity of the glycan. Using this custom-built synthesizer, as many as 15 reaction cycles can be performed in an automated fashion without a need for lyophilization or buffer exchange steps

Streamlining the chemoenzymatic synthesis of complex N-glycans by a stop and go strategy

Contemporary chemoenzymatic approaches can provide highly complex multi-antennary N-linked glycans. These procedures are, however, very demanding and typically involve as many as 100 chemical steps to prepare advanced intermediates that can be diversified by glycosyltransferases in a branch-selective manner to give asymmetrical structures commonly found in nature. Only highly specialized laboratories can perform such syntheses, which greatly hampers progress in glycoscience. Here we describe a biomimetic approach in which a readily available bi-antennary glycopeptide can be converted in ten or fewer chemical and enzymatic steps into multi-antennary N-glycans that at each arm can be uniquely extended by glycosyltransferases to give access to highly complex asymmetrically branched N-glycans. A key feature of our approach is the installation of additional branching points using recombinant MGAT4 and MGAT5 in combination with unnatural sugar donors. At an appropriate point in the enzymatic synthesis, the unnatural monosaccharides can be converted into their natural counterpart, allowing each arm to be elaborated into a unique appendage

Streamlining the chemoenzymatic synthesis of complex N-glycans by a stop and go strategy

Contemporary chemoenzymatic approaches can provide highly complex multi-antennary N-linked glycans. These procedures are, however, very demanding and typically involve as many as 100 chemical steps to prepare advanced intermediates that can be diversified by glycosyltransferases in a branch-selective manner to give asymmetrical structures commonly found in nature. Only highly specialized laboratories can perform such syntheses, which greatly hampers progress in glycoscience. Here we describe a biomimetic approach in which a readily available bi-antennary glycopeptide can be converted in ten or fewer chemical and enzymatic steps into multi-antennary N-glycans that at each arm can be uniquely extended by glycosyltransferases to give access to highly complex asymmetrically branched N-glycans. A key feature of our approach is the installation of additional branching points using recombinant MGAT4 and MGAT5 in combination with unnatural sugar donors. At an appropriate point in the enzymatic synthesis, the unnatural monosaccharides can be converted into their natural counterpart, allowing each arm to be elaborated into a unique appendage

Downstream Products are Potent Inhibitors of the Heparan Sulfate 2-O-Sulfotransferase.

Heparan Sulfate (HS) is a cell signaling molecule linked to pathological processes ranging from cancer to viral entry, yet fundamental aspects of its biosynthesis remain incompletely understood. Here, the binding preferences of the uronyl 2-O-sulfotransferase (HS2ST) are examined with variably-sulfated hexasaccharides. Surprisingly, heavily sulfated oligosaccharides formed by later-acting sulfotransferases bind more tightly to HS2ST than those corresponding to its natural substrate or product. Inhibition assays also indicate that the IC50 values correlate simply with degree of oligosaccharide sulfation. Structural analysis predicts a mode of inhibition in which 6-O-sulfate groups located on glucosamine residues present in highly-sulfated oligosaccharides occupy the canonical binding site of the nucleotide cofactor. The unexpected finding that oligosaccharides associated with later stages in HS biosynthesis inhibit HS2ST indicates that the enzyme must be separated temporally and/or spatially from downstream products during biosynthesis in vivo, and highlights a challenge for the enzymatic synthesis of lengthy HS chains in vitro

hFUT1-Based Live-Cell Assay To Profile alpha 1-2-Fucoside-Enhanced Influenza Virus A Infection

Host cell surface glycans play critical roles in influenza virus A (IVA) infection ranging from modulation of IVA attachment to membrane fusion and host tropism. Approaches for quick and sensitive profile of viral avidity toward a specific type of host cell glycan can contribute to the understanding of tropism switching among different IVA strains. Here, we developed a method based on chemoenzymatic glycan engineering to investigate the possible involvement of alpha 1-2-fucosides in WA infections. Using a truncated human fiicosyltransferase 1 (hFUT1), we created alpha 1-2-ficosides in situ on host cells to assess their influence on the host cell binding to IVA hemagglutinin and the susceptibility of host cells toward IVA-induced killing. We discovered that the newly created alpha 1-2-fucosides on host cells enhanced the infection of several human pandemic IVA subtypes either directly or indirectly. These findings suggest that glycan epitopes other than sialic acid should also be considered for assessing the human pandemic risk of this viral pathogen

Downstream Products are Potent Inhibitors of the Heparan Sulfate 2-O-Sulfotransferase.

Heparan Sulfate (HS) is a cell signaling molecule linked to pathological processes ranging from cancer to viral entry, yet fundamental aspects of its biosynthesis remain incompletely understood. Here, the binding preferences of the uronyl 2-O-sulfotransferase (HS2ST) are examined with variably-sulfated hexasaccharides. Surprisingly, heavily sulfated oligosaccharides formed by later-acting sulfotransferases bind more tightly to HS2ST than those corresponding to its natural substrate or product. Inhibition assays also indicate that the IC50 values correlate simply with degree of oligosaccharide sulfation. Structural analysis predicts a mode of inhibition in which 6-O-sulfate groups located on glucosamine residues present in highly-sulfated oligosaccharides occupy the canonical binding site of the nucleotide cofactor. The unexpected finding that oligosaccharides associated with later stages in HS biosynthesis inhibit HS2ST indicates that the enzyme must be separated temporally and/or spatially from downstream products during biosynthesis in vivo, and highlights a challenge for the enzymatic synthesis of lengthy HS chains in vitro

Author Correction: Downstream Products are Potent Inhibitors of the Heparan Sulfate 2-O-Sulfotransferase.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Structural basis for Lewis antigen synthesis by the α1,3-fucosyltransferase FUT9

Mammalian cell surface and secreted glycoproteins exhibit remarkable glycan structural diversity that contributes to numerous physiological and pathogenic interactions. Terminal glycan structures include Lewis antigens synthesized by a collection of α1,3/4-fucosyltransferases (CAZy GT10 family). At present, the only available crystallographic structure of a GT10 member is that of the Helicobacter pylori α1,3-fucosyltransferase, but mammalian GT10 fucosyltransferases are distinct in sequence and substrate specificity compared with the bacterial enzyme. Here, we determined crystal structures of human FUT9, an α1,3-fucosyltransferase that generates Lewisx and Lewisy antigens, in complex with GDP, acceptor glycans, and as a FUT9–donor analog–acceptor Michaelis complex. The structures reveal substrate specificity determinants and allow prediction of a catalytic model supported by kinetic analyses of numerous active site mutants. Comparisons with other GT10 fucosyltransferases and GT-B fold glycosyltransferases provide evidence for modular evolution of donor- and acceptor-binding sites and specificity for Lewis antigen synthesis among mammalian GT10 fucosyltransferases. [Figure not available: see fulltext.