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Binding modes of antigenically drifted hemagglutinins of human influenza A viruses have been determined by NMR using synthetic N-glycans having ¹³C-labeled monosaccharides to pinpoint which monosaccharides of extended LacNAc chains engage with the HAs.

While enzyme-mediated oligosaccharide synthesis is versatile, it is often limited by the availability of glycosyl transferases. Now a chemoenzymatic strategy is reported, comprising enzymatic assembly of a core oligosaccharide followed by chemical manipulations, to produce a library of glycans that reveal binding specificities of serum antibodies.

O-acetylation is a common modification of sialic acids. Here, a library of synthetic O-acetylated sialosides made it possible to develop an ion mobility mass spectrometry (IM-MS) approach that can elucidate exact O-acetylation patterns and glycosidic linkage types of sialosides isolated from biological samples.

Here, Broszeit et al. show that circulating A/H3N2 viruses have evolved binding specificity to α2,6-sialosides on extended LacNAc moieties and therefore cannot agglutinate erythrocytes. Applying glycan remodeling allows to install functional receptors on erythrocytes and promotes identification of newly circulating variants to facilitate vaccine design.

The specificity of human and animal viruses that engage with O-acetylated sialic acids has now been probed using a collection of O-acetylated sialoglycans obtained by diversification of trisaccharide precursors with viral haemagglutinin–esterases. The results revealed host-specific patterns of receptor recognition and showed that human respiratory viruses uniquely employ 9-O-acetylated α2,8-linked disialosides as receptors.

Seasonal influenza levels were unusually low when non-pharmaceutical interventions for COVID-19 were in place. Here, the authors analyse serological and epidemiological evidence for the hypothesis that such lulls in influenza transmission lead to reduced immunity and therefore larger epidemics in subsequent seasons.

Binding of a sialoglycan-based primary receptor by the spike protein of the common cold human coronavirus HKU1 triggers conformational changes to a state that would allow binding to a second receptor required for cell entry.

Preparation of well-defined N-glycans is very demanding, which hampers progress in glycoscience. Now, a biomimetic synthetic approach has been developed in which a readily available bi-antennary glycan can be converted in ten or fewer steps into multi-antennary N-glycans. This approach enables each arm to be uniquely extended by glycosyltransferases to give complex branched N-glycans.

The structure, molecular and mechanistic details of the human α1,3-fucosyltransferase FUT9 provide insight into the synthesis of diverse and modified glycan-capping Lewis antigen structures by a conserved family of mammalian fucosyltransferases.

Distinguishing proteoforms and post-translational modifications has remained a challenge. Here the authors explore single-molecule fluorescence resonance energy transfer to probe amino acids via DNA exchange and map the location of individual amino acids and post-translational modifications within single full-length protein molecules.

Matriglycan, a repeating disaccharide on α-dystroglycan, is the receptor for Lassa virus and specific extracellular matrix proteins. Here, the authors demonstrate that matriglycan, in a length-dependent tunable manner, is both necessary and sufficient for protein binding and viral infection.

The recently identified Wuhan spiny eel influenza virus (WSEIV) sequence is more closely related to influenza B than A viruses. Here, the authors functionally characterize the putative surface glycoproteins of WSEIV and show that its NA-like protein has sialidase activity and its HA-like protein binds monosialic ganglioside 2.

Heparan sulfates (HS) contain functionally relevant structural motifs, but determining their monosaccharide sequence remains challenging. Here, the authors develop an ion mobility mass spectrometry-based method that allows unambiguous characterization of HS sequences and structure-activity relationships.

Glycosylation can affect biological targets transiently and at low levels, making the development of diagnostic tools of critical importance. The application of a new series of antibodies raised against GlcNAc-modified substrates identifies a host of protein targets in normal and traumatized cells.

Mass spectrometric profiling of a glycan library reveals that sialylated glycans, especially sialic acid-containing gangliosides, interact with the RBD of the SARS-CoV-2 spike protein and are involved in ACE2-dependent viral infection.

An automated platform that can synthesize a wide range of complex glycans could greatly facilitate progress in glycoscience. Now, a fully automated process for enzyme-mediated oligosaccharide synthesis has been developed. This process uses glycosyltransferase-catalysed reactions performed in solution, with product purification being accomplished by solid phase extraction using a sulfonate tag.

Structural and functional analyses reveal how 9-O-acetyl sialic acid is recognized by the human coronavirus OC43 S glycoprotein and how this interaction promotes viral entry.

The difficulty in the stereoselective introduction of 1,2-cis-glycosides is a major stumbling block in the solid-supported synthesis of oligosaccharides. Now, this has been achieved for a biologically important glucoside containing multiple 1,2-cis-glycosidic linkages with complete anomeric control by using glycosyl donors having a participating (S)-(phenylthiomethyl)benzyl chiral auxiliary at C-2.

Mammalian peptidoglycan recognition proteins (PGRPs) are innate immune effectors that kill bacteria by unclear mechanisms. Kashyap et al. now provide insight into this question and report that PGRPs activate the bacterial two-component system that normally rids the cell of unfolded proteins. PGRP activation of this system abrogates metabolic functions, leading to accumulation of hydroxyl radicals and bacterial cell death.

Mucopolysaccharidoses are caused by a deficiency in GAG processing and can often be treated if the dysfunctional enzyme can be identified. A chemical derivatization strategy in combination with biochemical logic now yields a series of biomarkers that can be used to distinguish these disorders.

A chemically synthesized analog of Bacillus cereus secondary cell wall polysaccharide (SCWP) facilitates the identification of PatB1 as a SCWP O-acetyltransferase, and the structure of PatB1 provides insights into its catalytic mechanism.

IgG glycosylation is an important factor in immune function, yet the molecular details of protein glycosylation remain poorly understood. The data-driven approach presented here uses large-scale plasma IgG mass spectrometry measurements to infer new biochemical reactions in the glycosylation pathway.

The development of general synthetic strategies for the prepartion of oligonucleotides and peptides has enabled them to be made routinely — often using automated systems. Making complex oligosaccharides is much less straightforward, but advances in areas such as one-pot multi-step protecting-group manipulations, stereoselective glycosylation protocols and chemo-enzymatic methods are offering new opportunities for carbohydrate chemistry.