Epistasis in the receptor binding domain of contemporary H3N2 viruses that reverted to bind sialylated diLacNAc repeats.

Since the introduction of H3N2 influenza A viruses in the human population, these viruses have continuously evolved to escape human immunity, with mutations occurring in and around the receptor binding site. This process, called antigenic drift, recently resulted in viruses that recognize elongated glycans that are not abundantly displayed in the human respiratory tract. Such receptor specificities hampered our ability to pick and propagate vaccine strains.

The mammary glands of cows abundantly display receptors for circulating avian H5 viruses.

Influenza A viruses (IAVs) from the H5N1 2.3.4.

Direct and Ultrasensitive Bioluminescent Detection of Intact Respiratory Viruses.

Respiratory viruses such as SARS-CoV-2, influenza, and respiratory syncytial virus (RSV) represent pressing health risks. Rapid diagnostic tests for these viruses detect single antigens or nucleic acids, which do not necessarily correlate with the amount of the intact virus. Instead, specific detection of intact respiratory virus particles may be more effective at assessing the contagiousness of a patient.

Receptor Binding Specificity of a Bovine A(H5N1) Influenza Virus.

Outbreaks in the US of highly pathogenic avian influenza virus (H5N1) in dairy cows have been occurring for months creating new possibilities for direct contact between the virus and humans. Eisfeld examined the pathogenicity and transmissibility of a bovine HPAI H5N1 virus isolated from New Mexico in a series of and assays. They found the virus has a dual human- and avian virus-like receptor-binding specificity as measured in a solid phase glycan binding assay.

Salivary polyreactive antibodies and are associated with respiratory infection severity in young children with recurrent respiratory infections.

Background: Recurrent respiratory tract infections (rRTIs) are a common reason for immunodiagnostic testing in children, which relies on serum antibody level measurements. However, because RTIs predominantly affect the respiratory mucosa, serum antibodies may inaccurately reflect local immune defences. We investigated antibody responses in saliva and their interplay with the respiratory microbiota in relation to RTI severity and burden in young children with rRTIs.

H19 influenza A virus exhibits species-specific MHC class II receptor usage.

Avian influenza A virus (IAV) surveillance in Northern California, USA, revealed unique IAV hemagglutinin (HA) genome sequences in cloacal swabs from lesser scaups. We found two closely related HA sequences in the same duck species in 2010 and 2013. Phylogenetic analyses suggest that both sequences belong to the recently discovered H19 subtype, which thus far has remained uncharacterized.

The HCoV-HKU1 N-terminal domain binds a wide range of 9--acetylated sialic acids presented on different glycan cores.

Coronaviruses recognize a wide array of protein and glycan receptors using the S1 subunit of the spike (S) glycoprotein. The S1 subunit contains two functional domains: the N-terminal (S1-NTD) and C-terminal (S1-CTD). The S1-NTD of SARS-CoV-2, MERS-CoV, and HCoV-HKU1 possess an evolutionarily conserved glycan binding cleft that facilitates weak interactions with sialic acids on cell surfaces.

Long-term evolution of human seasonal influenza virus A(H3N2) is associated with an increase in polymerase complex activity.

Since the influenza pandemic in 1968, influenza A(H3N2) viruses have become endemic. In this state, H3N2 viruses continuously evolve to overcome immune pressure as a result of prior infection or vaccination, as is evident from the accumulation of mutations in the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). However, phylogenetic studies have also demonstrated ongoing evolution in the influenza A(H3N2) virus RNA polymerase complex genes.

Probing altered receptor specificities of antigenically drifting human H3N2 viruses by chemoenzymatic synthesis, NMR, and modeling.

Prototypic receptors for human influenza viruses are N-glycans carrying α2,6-linked sialosides. Due to immune pressure, A/H3N2 influenza viruses have emerged with altered receptor specificities that bind α2,6-linked sialosides presented on extended N-acetyl-lactosamine (LacNAc) chains. Here, binding modes of such drifted hemagglutinin's (HAs) are examined by chemoenzymatic synthesis of N-glycans having C-labeled monosaccharides at strategic positions.

Chemoenzymatic Synthesis of Tri-antennary N-Glycans Terminating in Sialyl-Lewis Reveals the Importance of Glycan Complexity for Influenza A Virus Receptor Binding.

Sialyl-Lewis (SLe) is involved in immune regulation, human fertilization, cancer, and bacterial and viral diseases. The influence of the complex glycan structures, which can present SLe epitopes, on binding is largely unknown. We report here a chemoenzymatic strategy for the preparation of a panel of twenty-two isomeric asymmetrical tri-antennary N-glycans presenting SLe-Le epitopes on either the MGAT4 or MGAT5 arm that include putative high-affinity ligands for E-selectin.

Viral envelope proteins fused to multiple distinct fluorescent reporters to probe receptor binding.

Enveloped viruses carry one or multiple proteins with receptor-binding functionalities. Functional receptors can be glycans, proteinaceous, or both; therefore, recombinant protein approaches are instrumental in attaining new insights regarding viral envelope protein receptor-binding properties. Visualizing and measuring receptor binding typically entails antibody detection or direct labeling, whereas direct fluorescent fusions are attractive tools in molecular biology.

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--acetyllactosamine (LacNAc) chains to provide any structural element of KS by using specific enzyme modules.

Complex -glycans are important for interspecies transmission of H7 influenza A viruses.

Influenza A viruses (IAVs) can overcome species barriers by adaptation of the receptor-binding site of the hemagglutinin (HA). To initiate infection, HAs bind to glycan receptors with terminal sialic acids, which are either -acetylneuraminic acid (NeuAc) or -glycolylneuraminic acid (NeuGc); the latter is mainly found in horses and pigs but not in birds and humans. We investigated the influence of previously identified equine NeuGc-adapting mutations (S128T, I130V, A135E, T189A, and K193R) in avian H7 IAVs and .

Asymmetrical Biantennary Glycans Prepared by a Stop-and-Go Strategy Reveal Receptor Binding Evolution of Human Influenza A Viruses.

Glycan binding properties of respiratory viruses have been difficult to probe due to a lack of biologically relevant glycans for binding studies. Here, a stop-and-go chemoenzymatic methodology is presented that gave access to a panel of 32 asymmetrical biantennary -glycans having various numbers of -acetyl lactosamine (LacNAc) repeating units capped by α2,3- or α2,6-sialosides resembling structures found in airway tissues. It exploits that the branching enzymes MGAT1 and MGAT2 can utilize unnatural UDP-2-deoxy-2-trifluoro--acetamido-glucose (UDP-GlcNTFA) as donor.

Bioluminescent detection of viral surface proteins using branched multivalent protein switches.

Fast and reliable virus diagnostics is key to prevent the spread of viruses in populations. A hallmark of viruses is the presence of multivalent surface proteins, a property that can be harnessed to control conformational switching in sensor proteins. Here, we introduce a new sensor platform (dark-LUX) for the detection of viral surface proteins consisting of a general bioluminescent framework that can be post-translationally functionalized with separately expressed binding domains.

Determinants of epidemic size and the impacts of lulls in seasonal influenza virus circulation.

During the COVID-19 pandemic, levels of seasonal influenza virus circulation were unprecedentedly low, leading to concerns that a lack of exposure to influenza viruses, combined with waning antibody titres, could result in larger and/or more severe post-pandemic seasonal influenza epidemics. However, in most countries the first post-pandemic influenza season was not unusually large and/or severe. Here, based on an analysis of historical influenza virus epidemic patterns from 2002 to 2019, we show that historic lulls in influenza virus circulation had relatively minor impacts on subsequent epidemic size and that epidemic size was more substantially impacted by season-specific effects unrelated to the magnitude of circulation in prior seasons.

Exploiting Substrate Specificities of 6--Sulfotransferases to Enzymatically Synthesize Keratan Sulfate Oligosaccharides.

Keratan sulfate (KS) is a glycosaminoglycan that is widely expressed in the extracellular matrix of various tissue types, where it is involved in many biological processes. Herein, we describe a chemo-enzymatic approach to preparing well-defined KS oligosaccharides by exploiting the known and newly discovered substrate specificities of relevant sulfotransferases. The premise of the approach is that recombinant GlcNAc-6--sulfotransferases (CHST2) only sulfate terminal GlcNAc moieties to give GlcNAc6S that can be galactosylated by B4GalT4.

Asymmetrical Bi-antennary Glycans Prepared by a Stop-and-Go Strategy Reveal Receptor Binding Evolution of Human Influenza A Viruses.

Glycan binding properties of respiratory viruses have been difficult to probe due to a lack of biological relevant glycans for binding studies. Here, a stop-and-go chemoenzymatic methodology is presented that gave access to a panel of 32 asymmetrical bi-antennary -glycans having various numbers of -acetyl lactosamine (LacNAc) repeating units capped by α2,3- or α2,6-sialosides resembling structures found in airway tissues. It exploits that the branching enzymes MGAT1 and MGAT2 can utilize unnatural UDP-2-deoxy-2-trifluoro--acetamido-glucose (UDP-GlcNTFA) as donor.

Chemo-Enzymatic Synthesis of Isomeric I-branched Polylactosamines Using Traceless Blocking Groups.

Poly-N-acetyl lactosamines (polyLacNAc) are common structural motifs of N- and O-linked glycan, glycosphingolipids and human milk oligosaccharides. They can be branched by the addition of β1,6-linked N-acetyl-glucosamine (GlcNAc) moieties to internal galactoside (Gal) residues by the I-branching enzyme beta-1,6-N-acetylglucosaminyltransferase 2 (GCNT2). I-branching has been implicated in many biological processes and is also associated with various diseases such as cancer progression.

Sialic acid O-acetylation patterns and glycosidic linkage type determination by ion mobility-mass spectrometry.

O-acetylation is a common modification of sialic acids that has been implicated in a multitude of biological and disease processes. A lack of analytical methods that can determine exact structures of sialic acid variants is a hurdle to determine roles of distinct O-acetylated sialosides. Here, we describe a drift tube ion mobility-mass spectrometry approach that can elucidate exact O-acetylation patterns as well as glycosidic linkage types of sialosides isolated from complex biological samples.

Continued adaptation of A/H2N2 viruses during pandemic circulation in humans.

Influenza A viruses of the H2N2 subtype sparked a pandemic in 1957 and circulated in humans until 1968. Because A/H2N2 viruses still circulate in wild birds worldwide and human population immunity is low, the transmissibility of six avian A/H2N2 viruses was investigated in the ferret model. None of the avian A/H2N2 viruses was transmitted between ferrets, suggesting that their pandemic risk may be low.

SARS-CoV-2 Spike N-Terminal Domain Engages 9--Acetylated α2-8-Linked Sialic Acids.

SARS-CoV-2 viruses engage ACE2 as a functional receptor with their spike protein. The S1 domain of the spike protein contains a C-terminal receptor binding domain (RBD) and an N-terminal domain (NTD). The NTD of other coronaviruses includes a glycan binding cleft.

Well-Defined Heparin Mimetics Can Inhibit Binding of the Trimeric Spike of SARS-CoV-2 in a Length-Dependent Manner.

The emergence of new SARS-CoV-2 variants and the dangers of long-covid necessitate the development of broad-acting therapeutics that can reduce viral burden. SARS-CoV-2 employs heparan sulfate (HS) as an initial cellular attachment factor, and therefore, there is interest in developing heparin as a therapeutic for SARS-CoV-2. Its use is, however, complicated by structural heterogeneity and the risk of causing bleeding and thrombocytopenia.