Effects of Sialic Acid Modifications on Virus Binding and Infection

The use of sialic acids as attachment factors is a common feature of Enterovirus-D species

Among the hundreds of enteroviruses (EVs) infecting humans, the members of the species EV-D (Enterovirus deconjuncti) display original traits. First, only five serotypes are known within this species, while other EV species have tens of serotypes each. Second, EV-Ds display a wide variety of tropisms: EV-D68s are respiratory viruses, EV-D70s have an ocular tropism, while EV-D94s, EV-D111s, and EV-D120s seem to be enteric viruses. Besides, while EV-D68s, EV-D70s, and EV-D94s have been detected in humans, EV-D120s were found exclusively in non-human primates, and the last virus type, EV-D111, was found in both. This and other observations have led to the hypothesis that EV-Ds could have a zoonotic origin. Previous studies have shown that EV-D68, EV-D70, and EV-D94 use sialic acids (Sias) as cellular attachment factors. We investigated the role of Sias in EV-D111 infection using sialidase treatments and loss-of-function experiments in human and simian cells. Assessing viral RNA yield by RT-qPCR analyses and infectious viral particle production by titration assays showed that the absence of Sias at the cell surface significantly slowed down EV-D111 infection kinetics without abolishing it. This suggests that Sia acts as an attachment factor. While EVs generally do not use Sias, EV-Ds seem to rely on them for optimal replication in cultured cells. Sia usage may therefore be an ancestral trait of this species. We also studied EV-B114, a simian enterovirus, and found that it does not use Sias. Our work provides new insight regarding an enterovirus that circulates in humans and exhibits unusual ecological traits.IMPORTANCEExcept for a few epidemics in the 1970s and 1980s, the impact of EV-Ds on human health remained modest until the 2010s. In 2014, EV-D68 was occasionally responsible for severe respiratory distress and fatal cases of muscular paralysis. EV-Ds have thus the ability to become pathogenic in humans, hence the importance of studying them. The recently discovered EV-D111, of which only a few isolates are available, has been detected in both human and simian samples, suggesting a potential zoonotic origin. We characterized the early steps of EV-D111 replication, with a focus on its ability to use Sias as attachment factors. We found that EV-D111, like other members of the EV-D species, but unlike most EVs, relies on Sia for optimal replication. Our work provides a better understanding of EV-D111 biology, which is essential to determine its tropism and its potential to emerge in humans.

A review on the development of sialyltransferase inhibitors

Sialylation of terminal glycoconjugates is involved in many important physiological and pathological processes such as tumor metastasis, drug resistance, organismal immunity, and viral infections. Sialyltransferases are enzymes responsible for sialylation modification in organisms, and potent sialyltransferase inhibitors can not only serve as probes for glycobiology studies, but also hold great promise to become agents for tumor therapy and viral infection control in the clinic. This review summarizes the latest progress in the development and application of various sialyltransferase inhibitors. The current challenges and development trends are also discussed.

Cell binding, uptake, and infection of influenza A virus using recombinant antibody-based receptors

Human and avian influenza A viruses bind to sialic acid (Sia) receptors on cells as their primary receptors, and this results in endocytic uptake of the virus. While the role of Sia on glycoproteins and/or glycolipids for virus entry is crucial, the roles of the carrier proteins are still not well understood. Furthermore, it is still unclear how receptor binding leads to infection, including whether the receptor plays a structural or other roles beyond being a simple tether. To enable the investigation of the receptor binding and cell entry processes in a more controlled manner, we have designed a protein receptor for pandemic H1 influenza A viruses. The engineered receptor possesses the binding domains of an anti-HA antibody prepared as a single-chain variable fragment (scFv) fused with the stalk, transmembrane, and cytoplasmic sequences of the feline transferrin receptor type-1 (fTfR). When expressed in cells that lack efficient display of Sia due to a knockout of the Slc35A1 gene, which encodes for the solute carrier family 35 transporter (SLC35A1), the anti-H1 receptor was displayed on the cell surface, bound virus, or hemagglutinin proteins, and the virus was efficiently endocytosed into the cells. Infection occurred at similar levels to those seen after reintroducing Sia expression, and lower affinity receptor mutants displayed enhanced infections. Treatment with clathrin-mediated endocytosis (CME) inhibitors significantly reduced viral entry, indicating that virus rescue by the antibody-based receptor follows a similar internalization route as Sia-expressing cells.IMPORTANCEInfluenza A viruses primarily circulate among avian reservoir hosts but can also jump species, causing outbreaks in mammals, including humans. A key interaction of the viruses is with host cell sialic acids, which vary in chemical form, in their linkages within the oligosaccharide, and in their display on various surface glycoproteins or glycolipids with differing properties. Here, we report a new method for examining the processes of receptor binding and uptake into cells during influenza A virus infection, by use of an engineered HA-binding membrane glycoprotein, where antibody variable domains are used to bind the virus, and the transferrin receptor uptake structures mediate efficient entry. This will allow us to test and manipulate the processes of cell binding, entry, and infection.

The physiological characteristics and applications of sialic acid

Sialic acid (SA) is widely present at the end of the sugar chain of glycoproteins and glycolipids on the surface of animal and microbial cells and is involved in many physiological activities between microbial and host cells. Notably, these functions are attributed to the diversity of these SA types, their different transformation pathways, and their metabolic actions within the host, which are considered potential targets for affecting various diseases. However, developing disease mitigation strategies is often limited by an unclear understanding of the mechanisms of interaction of the causative agents with their hosts. This review mainly focuses on three types of SA: Neu5Ac, Neu5Gc, and KDN. The sources, main types, and distribution of these SAs are discussed in detail, emphasizing the metabolic processes of different SAs and their interaction mechanisms with the host. This review will help lay a foundation for developing functional foods and SA-targeted intervention strategies.

Intestinal mucus: the unsung hero in the battle against viral gastroenteritis

Intestinal mucus plays a crucial role in defending against enteric infections by protecting the vulnerable intestinal epithelial cells both physically and through its various constituents. Despite this, numerous gastroenteritis-causing viruses, such as rotavirus, coronavirus, adenovirus, astrovirus, calicivirus, and enterovirus, continue to pose significant threats to humans and animals. While several studies have examined the interactions between these viruses and intestinal mucus, significant gaps remain in understanding the full protective potential of intestinal mucus against these pathogens. This review aims to elucidate the protective role of intestinal mucus in viral gastroenteritis. It begins with a comprehensive literature overview of (i) intestinal mucus, (ii) enteric viruses of medical and veterinary importance, and (iii) the known interactions between various enteric viruses and intestinal mucus. Following this, a case study is presented to highlight the age-dependent blocking effect of porcine intestinal mucus against transmissible gastroenteritis virus, a porcine coronavirus. Finally, the review discusses future investigation directions to further explore the potential of intestinal mucus as a defense mechanism against viral gastroenteritis to stimulate further research in this dynamic and critical area.

Extended receptor repertoire of an adenovirus associated with human obesity

Human adenovirus type 36 (HAdV-D36) has been putatively linked to obesity in animals and has been associated with obesity in humans in some but not all studies. Despite extensive epidemiological research there is limited information about its receptor profile. We investigated the receptor portfolio of HAdV-D36 using a combined structural biology and virology approach. The HAdV-D36 fiber knob domain (FK), which mediates the primary attachment of many HAdVs to host cells, has a significantly elongated DG loop that alters known binding interfaces for established adenovirus receptors such as the coxsackie- and adenovirus receptor (CAR) and CD46. Our data suggest that HAdV-D36 attaches to host cells using a versatile receptor pool comprising sialic acid-containing glycans and CAR. Sialic acids are recognized at the same binding site used by other HAdVs of species D such as HAdV-D37. Using glycan microarrays, we demonstrate that HAdV-D36 displays a binding preference for glycans containing a rare sialic acid variant, 4-O,5-N-diacetylneuraminic acid, over the more common 5-N-acetylneuraminic acid. To date, this sialic acid variant has not been detected in humans, although it can be synthesized by various animal species, including a range of domestic and livestock animals. Taken together, our results indicate that HAdV-D36 has evolved to recognize a specialized set of primary attachment receptors that are different from known HAdV types and coincides with a unique host range and pathogenicity profile.

The forecasting power of the mucin-microbiome interplay in livestock respiratory diseases

Complex respiratory diseases are a significant challenge for the livestock industry worldwide. These diseases considerably impact animal health and welfare and cause severe economic losses. One of the first lines of pathogen defense combines the respiratory tract mucus, a highly viscous material primarily composed of mucins, and a thriving multi-kingdom microbial ecosystem. The microbiome-mucin interplay protects from unwanted substances and organisms, but its dysfunction may enable pathogenic infections and the onset of respiratory disease. Emerging evidence also shows that noncoding regulatory RNAs might modulate the structure and function of the microbiome-mucin relationship. This opinion paper unearths the current understanding of the triangular relationship between mucins, the microbiome, and noncoding RNAs in the context of respiratory infections in animals of veterinary interest. There is a need to look at these molecular underpinnings that dictate distinct health and disease outcomes to implement effective prevention, surveillance, and timely intervention strategies tailored to the different epidemiological contexts.

The HCoV-HKU1 N-Terminal Domain Binds a Wide Range of 9-O-Acetylated Sialic Acids Presented on Different Glycan Cores

Coronaviruses (CoVs) recognize a wide array of protein and glycan receptors by using the S1 subunit of the spike (S) glycoprotein. The S1 subunit contains two functional domains: the N-terminal domain (S1-NTD) and the C-terminal domain (S1-CTD). The S1-NTD of SARS-CoV-2, MERS-CoV, and HCoV-HKU1 possesses an evolutionarily conserved glycan binding cleft that facilitates weak interactions with sialic acids on cell surfaces. HCoV-HKU1 employs 9-O-acetylated α2-8-linked disialylated structures for initial binding, followed by TMPRSS2 receptor binding and virus-cell fusion. Here, we demonstrate that the HCoV-HKU1 NTD has a broader receptor binding repertoire than previously recognized. We presented HCoV-HKU1 NTD Fc chimeras on a nanoparticle system to mimic the densely decorated surface of HCoV-HKU1. These proteins were expressed by HEK293S GnTI- cells, generating species carrying Man-5 structures, often observed near the receptor binding site of CoVs. This multivalent presentation of high mannose-containing NTD proteins revealed a much broader receptor binding profile compared to that of its fully glycosylated counterpart. Using glycan microarrays, we observed that 9-O-acetylated α2-3-linked sialylated LacNAc structures are also bound, comparable to OC43 NTD, suggesting an evolutionarily conserved glycan-binding modality. Further characterization of receptor specificity indicated promiscuous binding toward 9-O-acetylated sialoglycans, independent of the glycan core (glycolipids, N- or O-glycans). We demonstrate that HCoV-HKU1 may employ additional sialoglycan receptors to trigger conformational changes in the spike glycoprotein to expose the S1-CTD for proteinaceous receptor binding.

Structural and quantitative comparison of viral infection-associated N-glycans in plasma from humans, pigs, and chickens: Greater similarity between humans and chickens than pigs

Host N-glycans play an essential role in the attachment, invasion, and infection processes of viruses, including zoonotic infectious diseases. The similarity of N-glycans in the trachea and lungs of humans and pigs facilitates the cross-species transmission of influenza viruses through respiratory tracts. In this study, the structure and quantity of N-glycans in the plasma of humans, pigs, and chickens were analyzed using liquid chromatography-quadrupole-Orbitrap-tandem mass spectrometry. N-glycans in humans (35), pigs (28), and chickens (53) were identified, including the most abundant, species-common, and species-specific N-glycans. Among the N-glycans (relative quantity >0.5%), the sialic acid derivative of N-acetylneuraminic acid was identified in humans (the sum of the relative quantities of each; 64.3%), pigs (45.5%), and chickens (64.4%), whereas N-glycolylneuraminic acid was only identified in pigs (18.1%). Sialylated N-glycan linkage isomers are the influenza virus receptors (α2-6 in humans, α2-3 and α2-6 in pigs, and α2-3 in chickens). Only α2-6 linkages (human, 58.2%; pig, 44.8%; and chicken, 60.6%) were more abundant than α2-3/α2-6 linkages (human, 4.6%; pig, 0.6%; and chicken, 3.4%) and only α2-3 linkages (human, 1.5%; pig, 0.1%; and chicken, 0.4%). Fucosylation, which can promote viral infection through immune modulation, was more abundant in pigs (76.1%) than in humans (36.4%) and chickens (16.7%). Bisecting N-acetylglucosamine, which can suppress viral infection by inhibiting sialylation, was identified in humans (10.3%) and chickens (16.9%), but not in pigs. These results indicate that plasma N-glycans are similar in humans and chickens. This is the first study to compare plasma N-glycans in humans, pigs, and chickens.

Neuraminidase-1 (NEU1): Biological Roles and Therapeutic Relevance in Human Disease

Neuraminidases catalyze the desialylation of cell-surface glycoconjugates and play crucial roles in the development and function of tissues and organs. In both physiological and pathophysiological contexts, neuraminidases mediate diverse biological activities via the catalytic hydrolysis of terminal neuraminic, or sialic acid residues in glycolipid and glycoprotein substrates. The selective modulation of neuraminidase activity constitutes a promising strategy for treating a broad spectrum of human pathologies, including sialidosis and galactosialidosis, neurodegenerative disorders, cancer, cardiovascular diseases, diabetes, and pulmonary disorders. Structurally distinct as a large family of mammalian proteins, neuraminidases (NEU1 through NEU4) possess dissimilar yet overlapping profiles of tissue expression, cellular/subcellular localization, and substrate specificity. NEU1 is well characterized for its lysosomal catabolic functions, with ubiquitous and abundant expression across such tissues as the kidney, pancreas, skeletal muscle, liver, lungs, placenta, and brain. NEU1 also exhibits a broad substrate range on the cell surface, where it plays hitherto underappreciated roles in modulating the structure and function of cellular receptors, providing a basis for it to be a potential drug target in various human diseases. This review seeks to summarize the recent progress in the research on NEU1-associated diseases and highlight the mechanistic implications of NEU1 in disease pathogenesis. An improved understanding of NEU1-associated diseases should help accelerate translational initiatives to develop novel or better therapeutics.

Direct Glycan Analysis of Biological Samples and Intact Glycoproteins by Integrating Machine Learning-Driven Surface-Enhanced Raman Scattering and Boronic Acid Arrays

Frequent monitoring of glycan patterns is a critical step in studying glycan-mediated cellular processes. However, the current glycan analysis tools are resource-intensive and less suitable for routine use in standard laboratories. We developed a novel glycan detection platform by integrating surface-enhanced Raman spectroscopy (SERS), boronic acid (BA) receptors, and machine learning tools. This sensor monitors the molecular fingerprint spectra of BA binding to cis-diol-containing glycans. Different types of BA receptors could yield different stereoselective reactions toward different glycans and exhibit unique vibrational spectra. By integration of the Raman spectra collected from different BA receptors, the structural information can be enriched, eventually improving the accuracy of glycan classification and quantification. Here, we established a SERS-based sensor incorporating multiple different BA receptors. This sensing platform could directly analyze the biological samples, including whole milk and intact glycoproteins (fetuin and asialofetuin), without tedious glycan release and purification steps. The results demonstrate the platform's ability to classify milk oligosaccharides with remarkable classification accuracy, despite the presence of other non-glycan constituents in the background. This sensor could also directly quantify sialylation levels of a fetuin/asialofetuin mixture without glycan release procedures. Moreover, by selecting appropriate BA receptors, the sensor exhibits an excellent performance of differentiating between α2,3 and α2,6 linkages of sialic acids. This low-cost, rapid, and highly accessible sensor will provide the scientific community with an invaluable tool for routine glycan screening in standard laboratories.

The HCoV-HKU1 N-terminal domain binds a wide range of 9-O-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. HCoV-HKU1 employs 9-O-acetylated α2-8-linked disialylated structures for initial binding, followed by TMPRSS2 receptor binding and virus-cell fusion. Here, we demonstrate that HCoV-HKU1 NTD has a broader receptor binding repertoire than previously recognized. We presented HCoV-HKU1 NTD Fc chimeras on a nanoparticle system to mimic the densely decorated surface of HCoV-HKU1. These proteins were expressed by HEK293S GNTI- cells, generating species carrying Man-5 structures, often observed near the receptor binding site of CoVs. This multivalent presentation of high-mannose-containing NTD proteins revealed a much broader receptor binding profile compared to its fully glycosylated counterpart. Using glycan microarrays, we observed that 9-O-acetylated α2-3 linked sialylated LacNAc structures are also bound, comparable to OC43 NTD, suggesting an evolutionarily conserved glycan-binding modality. Further characterization of receptor specificity indicated promiscuous binding towards 9-O-acetylated sialoglycans, independent of the glycan core (glycolipids, N- or O-glycans). We demonstrate that HCoV-HKU1 may employ additional sialoglycan receptors to trigger conformational changes in the spike glycoprotein to expose the S1-CTD for proteinaceous receptor binding.

Sialic acids as attachment factors in mosquitoes mediating Japanese encephalitis virus infection

The role of Culex mosquitoes in the transmission of Japanese encephalitis virus (JEV) is crucial, yet the mechanisms of JEV infection in these vectors remain unclear. Previous research has indicated that various host factors participate in JEV infection. Herein, we present evidence that mosquito sialic acids enhance JEV infection both in vivo and in vitro. By treating mosquitoes and C6/36 cells with neuraminidase or lectin, the function of sialic acids is effectively blocked, resulting in significant inhibition of JEV infection. Furthermore, knockdown of the sialic acid biosynthesis genes in Culex mosquitoes also leads to a reduction in JEV infection. Moreover, our research revealed that sialic acids play a role in the attachment of JEV to mosquito cells, but not in its internalization. To further explore the mechanisms underlying the promotion of JEV attachment by sialic acids, we conducted immunoprecipitation experiments to confirm the direct binding of sialic acids to the last α-helix in JEV envelope protein domain III. Overall, our study contributes to a molecular comprehension of the interaction between mosquitoes and JEV and offers potential strategies for preventing the dissemination of flavivirus in natural environments.IMPORTANCEIn this study, we aimed to investigate the impact of glycoconjugate sialic acids on mosquito infection with Japanese encephalitis virus (JEV). Our findings demonstrate that sialic acids play a crucial role in enhancing JEV infection by facilitating the attachment of the virus to the cell membrane. Furthermore, our investigation revealed that sialic acids directly bind to the final α-helix in the JEV envelope protein domain III, thereby accelerating virus adsorption. Collectively, our results highlight the significance of mosquito sialic acids in JEV infection within vectors, contributing to a better understanding of the interaction between mosquitoes and JEV.

Analysis of O-acetylated sialic acids by 3-nitrophenylhydrazine derivatization combined with LC-MS/MS

Sialic acids are a family of monosaccharides that share a nine-carbon backbone and a carboxyl group. A recent derivatization method based on 3-nitrophenylhydrazine (3-NPH) provides a mild chemical labeling technique for biomolecules containing carbonyl or carboxyl groups. In this study, we utilized 3-NPH to label sialic acids via a two-step derivatization process. The derivatized species can produce a common reporter ion corresponding to C1-C3 with two labels, and a fragment differentiating between Neu5Ac, Neu5Gc, and KDN. This method is compatible with O-acetylated sialic acids and provides high sensitivity to Neu5Gc and KDN, and since the utilization of dual labeling significantly enhances the hydrophobicity of derivatives, it can effectively mitigate matrix effects when combined with parallel reaction monitoring technology. Negative-ion tandem mass spectrometry (MS/MS) analysis reveals a distinctive fragmentation profile for the 4-O-acetylated species, while the other sialic acids yield similar MS/MS spectra with a high abundance of reporter ions. Using the reporter ion as a transition, this analytical strategy is effective for analyzing complex biological samples. For example, it was successfully employed to quantify sialic acids in the intestinal tissues of several carp species, demonstrating its potential in sialylation research.

Uncloaking the viral glycocalyx: How do viruses exploit glycoimmune checkpoints?

The surfaces of cells and enveloped viruses alike are coated in carbohydrates that play multifarious roles in infection and immunity. Organisms across all kingdoms of life make use of a diverse set of monosaccharide subunits, glycosidic linkages, and branching patterns to encode information within glycans. Accordingly, sugar-patterning enzymes and glycan binding proteins play integral roles in cell and organismal biology, ranging from glycoprotein quality control within the endoplasmic reticulum to lymphocyte migration, coagulation, inflammation, and tissue homeostasis. Unsurprisingly, genes involved in generating and recognizing oligosaccharide patterns are playgrounds for evolutionary conflicts that abound in cross-species interactions, exemplified by the myriad plant lectins that function as toxins. In vertebrates, glycans bearing acidic nine-carbon sugars called sialic acids are key regulators of immune responses. Various bacterial and fungal pathogens adorn their cells in sialic acids that either mimic their hosts' or are stolen from them. Yet, how viruses commandeer host sugar-patterning enzymes to thwart immune responses remains poorly studied. Here, we review examples of viruses that interact with sialic acid-binding immunoglobulin-like lectins (Siglecs), a family of immune cell receptors that regulate toll-like receptor signaling and govern glycoimmune checkpoints, while highlighting knowledge gaps that merit investigation. Efforts to illuminate how viruses leverage glycan-dependent checkpoints may translate into new clinical treatments that uncloak viral antigens and infected cell surfaces by removing or masking immunosuppressive sialoglycans, or by inhibiting viral gene products that induce their biosynthesis. Such approaches may hold the potential to unleash the immune system to clear long intractable chronic viral infections.

Sialic acids in infection and their potential use in detection and protection against pathogens

In structural terms, the sialic acids are a large family of nine carbon sugars based around an alpha-keto acid core. They are widely spread in nature, where they are often found to be involved in molecular recognition processes, including in development, immunology, health and disease. The prominence of sialic acids in infection is a result of their exposure at the non-reducing terminus of glycans in diverse glycolipids and glycoproteins. Herein, we survey representative aspects of sialic acid structure, recognition and exploitation in relation to infectious diseases, their diagnosis and prevention or treatment. Examples covered span influenza virus and Covid-19, Leishmania and Trypanosoma, algal viruses, Campylobacter, Streptococci and Helicobacter, and commensal Ruminococci.

Milk Antiviral Proteins and Derived Peptides against Zoonoses

Milk is renowned for its nutritional richness but also serves as a remarkable reservoir of bioactive compounds, particularly milk proteins and their derived peptides. Recent studies have showcased several robust antiviral activities of these proteins, evidencing promising potential within zoonotic viral diseases. While several publications focus on milk's bioactivities, antiviral peptides remain largely neglected in reviews. This knowledge is critical for identifying novel research directions and analyzing potential nutraceuticals within the One Health context. Our review aims to gather the existing scientific information on milk-derived antiviral proteins and peptides against several zoonotic viral diseases, and their possible mechanisms. Overall, in-depth research has increasingly revealed them as a promising and novel strategy against viruses, principally for those constituting a plausible pandemic threat. The underlying mechanisms of the bioactivity of milk's proteins include inhibiting viral entry and attachment to the host cells, blocking replication, or even viral inactivation via peptide-membrane interactions. Their marked versatility and effectiveness stand out compared to other antiviral peptides and can support future research and development in the post-COVID-19 era. Overall, our review helps to emphasize the importance of potentially effective milk-derived peptides, and their significance for veterinary and human medicines, along with the pharmaceutical, nutraceutical, and dairy industry.

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. It is based on the use of a library of synthetic O-acetylated sialosides to establish intrinsic collision cross section (CCS) values of diagnostic fragment ions. The CCS values were used to characterize O-acetylated sialosides from mucins and N-linked glycans from biologicals as well as equine tracheal and nasal tissues. It uncovered contrasting sialic acid linkage types of acetylated and non-acetylated sialic acids and provided a rationale for sialic acid binding preferences of equine H7 influenza A viruses.

Chronic encephalomyelitis virus exhibits cellular tropism and evades pDCs by binding to sialylated integrins as the cell surface receptors

Theiler's murine encephalomyelitis virus (TMEV) causes a chronic demyelinating disease similar to multiple sclerosis in mice. Although sialic acids have been shown to be essential for TMEV attachment to the host, the surface receptor has not been identified. While type I interferons play a pivotal role in the elimination of the chronic infectious Daniel (DA) strain, the role of plasmacytoid dendritic cells (pDCs) is controversial. We herein found that TMEV binds to conventional DCs but not to pDCs. A glycomics analysis showed that the sialylated N-glycan fractions were lower in pDCs than in conventional DCs, indicating that pDCs are not susceptible to TMEV infection due to the low levels of sialic acid. TMEV capsid proteins contain an integrin recognition motif, and dot blot assays showed that the integrin proteins bind to TMEV and that the viral binding was reduced in the desialylated αX β2 . αX β2 protein suppressed TMEV replication in vivo, and TMEV co-localized with integrin αM at the cell membrane and TLR 3 in the cytoplasm, suggesting that αM serves as the viral attachment and entry. These results show that the chronic encephalomyelitis virus utilizes sialylated integrins as cell surface receptors, leading to cellular tropism to evade pDC activation.

Identification of Novel Glycans in the Mucus Layer of Shark and Skate Skin

The mucus layer covering the skin of fish has several roles, including protection against pathogens and mechanical damage. While the mucus layers of various bony fish species have been investigated, the composition and glycan profiles of shark skin mucus remain relatively unexplored. In this pilot study, we aimed to explore the structure and composition of shark skin mucus through histological analysis and glycan profiling. Histological examination of skin samples from Atlantic spiny dogfish (Squalus acanthias) sharks and chain catsharks (Scyliorhinus retifer) revealed distinct mucin-producing cells and a mucus layer, indicating the presence of a functional mucus layer similar to bony fish mucus albeit thinner. Glycan profiling using liquid chromatography-electrospray ionization tandem mass spectrometry unveiled a diverse repertoire of mostly O-glycans in the mucus of the two sharks as well as little skate (Leucoraja erinacea). Elasmobranch glycans differ significantly from bony fish, especially in being more sulfated, and some bear resemblance to human glycans, such as gastric mucin O-glycans and H blood group-type glycans. This study contributes to the concept of shark skin having unique properties and provides a foundation for further research into the functional roles and potential biomedical implications of shark skin mucus glycans.

Newly identified lineages of porcine hemagglutinating encephalomyelitis virus exhibit respiratory phenotype

Swine pathogens have a long history of zoonotic transmission to humans, occasionally leading to sustained outbreaks or pandemics. Through a retrospective epidemiological study of swine populations in China, we describe novel lineages of porcine hemagglutinating encephalomyelitis virus (PHEV) complex coronaviruses (CoVs) that cause exclusively respiratory symptoms with no signs of the neurological symptoms typically associated with classical PHEV infection. Through large-scale epidemiological surveillance, we show that these novel lineages have circulated in at least eight provinces in southeastern China. Phylogenetic and recombination analyses of twenty-four genomes identified two major viral lineages causing respiratory symptoms with extensive recombination within them, between them, and between classical PHEV and the novel respiratory variant PHEV (rvPHEV) lineages. Divergence times among the sampled lineages in the PHEV virus complex date back to 1886-1958 (mean estimate 1928), with the two major rvPHEV lineages separating approximately 20 years later. Many rvPHEV viruses show amino acid substitutions at the carbohydrate-binding site of hemagglutinin esterase (HE) and/or have lost the cysteine required for HE dimerization. This resembles the early adaptation of human CoVs, where HE lost its hemagglutination ability to adapt to growth in the human respiratory tract. Our study represents the first report of the evolutionary history of rvPHEV circulating in swine and highlights the importance of characterizing CoV diversity and recombination in swine to identify pathogens with outbreak potential that could threaten swine farming.

A novel strategy for quantification of α2,3- and α2,6-linked sialic acids in sialylated glycoproteins

Sialic acid, a monosaccharide containing nine carbon atoms, is widely distributed in eukaryotic cells. The bound sialic acids are mainly present at the glycan ends of glycoconjugates via α2-3 or α2-6 glycosidic bonds, and alterations in their expression levels and linkage types are associated with the progress of many diseases and tumors. The present study provides a new strategy for quantification of α2,3- and α2,6-linked sialic acids in sialylated glycoproteins. In fact, quantification of α2,3-linked sialic acids were based on the difference of the bound sialic acids in the sample before and after treatment with α2-3 neuraminidase, whereas the α2,6-linked sialic acids were equal to the bound sialic acids in the α2-3 neuraminidase-treated sample. Subsequently, α2,3/6-linked sialic acids in salivary glycoproteins from healthy volunteers and diabetic patients were quantified in accordance with this method. This work provides an accurate method for the quantification of α2,3- and α2,6-linked sialic acids in the sialoglycoproteins, which is more instructive for understanding the biological roles of α2,3/6-linked sialic acid in sialoglycoproteins.

Identification and Comparison of the Sialic Acid-Binding Domain Characteristics of Avian Coronavirus Infectious Bronchitis Virus Spike Protein

Infectious bronchitis virus (IBV) infections are initiated by the transmembrane spike (S) glycoprotein, which binds to host factors and fuses the viral and cell membranes. The N-terminal domain of the S1 subunit of IBV S protein binds to sialic acids, but the precise location of the sialic acid binding domain (SABD) and the role of the SABD in IBV-infected chickens remain unclear. Here, we identify the S1 N-terminal amino acid (aa) residues 19 to 227 (209 aa total) of IBV strains SD (GI-19) and GD (GI-7), and the corresponding region of M41 (GI-1), as the minimal SABD using truncated protein histochemistry and neuraminidase assays. Both α-2,3- and α-2,6-linked sialic acids on the surfaces of CEK cells can be used as attachment receptors by IBV, leading to increased infection efficiency. However, 9-O acetylation of the sialic acid glycerol side chain inhibits IBV S1 and SABD protein binding. We further constructed recombinant strains in which the S1 gene or the SABD in the GD and SD genomes were replaced with the corresponding region from M41 by reverse genetics. Infecting chickens with these viruses revealed that the virulence and nephrotropism of rSDM41-S1, rSDM41-206, rGDM41-S1, and rGDM41-206 strains were decreased to various degrees compared to their parental strains. A positive sera cross-neutralization test showed that the serotypes were changed for the recombinant viruses. Our results provide insight into IBV infection of host cells that may aid vaccine design. IMPORTANCE To date, only α-2,3-linked sialic acid has been identified as a potential host binding receptor for IBV. Here, we show the minimum region constituting the sialic acid binding domain (SABD) and the binding characteristics of the S1 subunit of spike (S) protein of IBV strains SD (GI-19), GD (GI-7), and M41 (GI-1) to various sialic acids. The 9-O acetylation modification partially inhibits IBV from binding to sialic acid, while the virus can also bind to sialic acid molecules linked to host cells through an α-2,6 linkage, serving as another receptor determinant. Substitution of the putative SABD from strain M41 into strains SD and GD resulted in reduced virulence, nephrotropism, and a serotype switch. These findings suggest that sialic acid binding has diversified during the evolution of γ-coronaviruses, impacting the biological properties of IBV strains. Our results offer insight into the mechanisms by which IBV invades host cells.

SARS-CoV-2 Spike N-Terminal Domain Engages 9-O-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. However, for the SARS-CoV-2 NTD, protein-glycan binding was only observed weakly for sialic acids with highly sensitive methods. Amino acid changes in the NTD of variants of concern (VoC) show antigenic pressure, which can be an indication of NTD-mediated receptor binding. Trimeric NTD proteins of SARS-CoV-2, alpha, beta, delta, and omicron did not reveal a receptor binding capability. Unexpectedly, the SARS-CoV-2 beta subvariant strain (501Y.V2-1) NTD binding to Vero E6 cells was sensitive to sialidase pretreatment. Glycan microarray analyses identified a putative 9-O-acetylated sialic acid as a ligand, which was confirmed by catch-and-release ESI-MS, STD-NMR analyses, and a graphene-based electrochemical sensor. The beta (501Y.V2-1) variant attained an enhanced glycan binding modality in the NTD with specificity toward 9-O-acetylated structures, suggesting a dual-receptor functionality of the SARS-CoV-2 S1 domain, which was quickly selected against. These results indicate that SARS-CoV-2 can probe additional evolutionary space, allowing binding to glycan receptors on the surface of target cells.

Dietary sialic acids: distribution, structure, and functions

Sialic acids (Sias), a group of over 50 structurally distinct acidic saccharides on the surface of all vertebrate cells, are neuraminic acid derivatives. They serve as glycan chain terminators in extracellular glycolipids and glycoproteins. In particular, Sias have significant implications in cell-to-cell as well as host-to-pathogen interactions and participate in various biological processes, including neurodevelopment, neurodegeneration, fertilization, and tumor migration. However, Sia is also present in some of our daily diets, particularly in conjugated form (sialoglycans), such as those in edible bird's nest, red meats, breast milk, bovine milk, and eggs. Among them, breast milk, especially colostrum, contains a high concentration of sialylated oligosaccharides. Numerous reviews have concentrated on the physiological function of Sia as a cellular component of the body and its relationship with the occurrence of diseases. However, the consumption of Sias through dietary sources exerts significant influence on human health, possibly by modulating the gut microbiota's composition and metabolism. In this review, we summarize the distribution, structure, and biological function of particular Sia-rich diets, including human milk, bovine milk, red meat, and egg.

Sialic acid exacerbates gut dysbiosis-associated mastitis through the microbiota-gut-mammary axis by fueling gut microbiota disruption

BACKGROUND

Mastitis is one of the most severe diseases in humans and animals, especially on dairy farms. Mounting evidence indicates that gastrointestinal dysbiosis caused by induction of subacute ruminal acidosis (SARA) by high-grain diet consumption and low in dietary fiber is associated with mastitis initiation and development, however, the underlying mechanism remains unknown.

RESULTS

In the present study, we found that cows with SARA-associated mastitis have altered metabolic profiles in the rumen, with increased sialic acids level in particular. Consumption of sialic acid (SA) in antibiotic-treated mice, but not healthy mice, induced marked mastitis. SA treatment of antibiotic-treated mice also induced mucosal and systemic inflammatory responses, as evidenced by increased colon and liver injuries and several inflammatory markers. In addition, gut dysbiosis caused by antibiotic impaired gut barrier integrity, which was aggravated by SA treatment. SA potentiated serum LPS level caused by antibiotic treatment, leading to increased activation of the TLR4-NF-κB/NLRP3 pathways in the mammary gland and colon. Moreover, SA facilitated gut dysbiosis caused by antibiotic, and especially enhanced Enterobacteriaceae and Akkermansiaceae, which correlated with mastitis parameters. Fecal microbiota transplantation from SA-antibiotic-treated mice mimicked mastitis in recipient mice. In vitro experiments showed that SA prompted Escherichia coli growth and virulence gene expression, leading to higher proinflammatory cytokine production in macrophages. Targeting the inhibition of Enterobacteriaceae by sodium tungstate or treating with the commensal Lactobacillus reuteri alleviated SA-facilitated mastitis. In addition, SARA cows had distinct ruminal microbial structure by the enrichment of SA-utilizing opportunistic pathogenic Moraxellaceae and the depletion of SA-utilizing commensal Prevotellaceae. Treating mice with the specific sialidase inhibitor zanamivir reduced SA production and Moraxellaceae abundance, and improved mastitis in mice caused by ruminal microbiota transplantation from cows with SARA-associated mastitis.

CONCLUSIONS

This study, for the first time, indicates that SA aggravates gut dysbiosis-induced mastitis by promoting gut microbiota disturbance and is regulated by commensal bacteria, indicating the important role of the microbiota-gut-mammary axis in mastitis pathogenesis and suggesting a potential strategy for mastitis intervention based on gut metabolism regulation. Video Abstract.

An In Silico Functional Analysis of Non-Synonymous Single-Nucleotide Polymorphisms of Bovine CMAH Gene and Potential Implication in Pathogenesis

The sugar molecule N-glycolylneuraminic acid (Neu5Gc) is one of the most common sialic acids discovered in mammals. Cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) catalyses the conversion of N-acetylneuraminic acid (Neu5Ac) to Neu5Gc, and it is encoded by the CMAH gene. On the one hand, food metabolic incorporation of Neu5Gc has been linked to specific human diseases. On the other hand, Neu5Gc has been shown to be highly preferred by some pathogens linked to certain bovine diseases. We used various computational techniques to perform an in silico functional analysis of five non-synonymous single-nucleotide polymorphisms (nsSNPs) of the bovine CMAH (bCMAH) gene identified from the 1000 Bull Genomes sequence data. The c.1271C>T (P424L) nsSNP was predicted to be pathogenic based on the consensus result from different computational tools. The nsSNP was also predicted to be critical based on sequence conservation, stability, and post-translational modification site analysis. According to the molecular dynamic simulation and stability analysis, all variations promoted stability of the bCMAH protein, but mutation A210S significantly promoted CMAH stability. In conclusion, c.1271C>T (P424L) is expected to be the most harmful nsSNP among the five detected nsSNPs based on the overall studies. This research could pave the way for more research associating pathogenic nsSNPs in the bCMAH gene with diseases.

Single Particle Analysis of H3N2 Influenza Entry Differentiates the Impact of the Sialic Acids (Neu5Ac and Neu5Gc) on Virus Binding and Membrane Fusion

Entry of influenza A viruses (IAVs) into host cells is initiated by binding to sialic acids (Sias), their primary host cell receptor, followed by endocytosis and membrane fusion to release the viral genome into the cytoplasm of the host cell. Host tropism is affected by these entry processes, with a primary factor being receptor specificity. Sias exist in several different chemical forms, including the hydroxylated N-glycolylneuraminic acid (Neu5Gc), which is found in many hosts; however, it has not been clear how modified Sias affect viral binding and entry. Neu5Gc is commonly found in many natural influenza hosts, including pigs and horses, but not in humans or ferrets. Here, we engineered HEK293 cells to express the hydoxylase gene (CMAH) that converts Neu5Ac to Neu5Gc, or knocked out the Sia-CMP transport gene (SLC35A1), resulting in cells that express 95% Neu5Gc or minimal level of Sias, respectively. H3N2 (X-31) showed significantly reduced infectivity in Neu5Gc-rich cells compared to wild-type HEK293 (>95% Neu5Ac). To determine the effects on binding and fusion, we generated supported lipid bilayers (SLBs) derived from the plasma membranes of these cells and carried out single particle microscopy. H3N2 (X-31) exhibited decreased binding to Neu5Gc-containing SLBs, but no significant difference in H3N2 (X-31)'s fusion kinetics to either SLB type, suggesting that reduced receptor binding does not affect subsequent membrane fusion. This finding suggests that for this virus to adapt to host cells rich in Neu5Gc, only receptor affinity changes are required without further adaptation of virus fusion machinery. IMPORTANCE Influenza A virus (IAV) infections continue to threaten human health, causing over 300,000 deaths yearly. IAV infection is initiated by the binding of influenza glycoprotein hemagglutinin (HA) to host cell sialic acids (Sias) and the subsequent viral-host membrane fusion. Generally, human IAVs preferentially bind to the Sia N-acetylneuraminic acid (Neu5Ac). Yet, other mammalian hosts, including pigs, express diverse nonhuman Sias, including N-glycolylneuraminic acid (Neu5Gc). The role of Neu5Gc in human IAV infections in those hosts is not well-understood, and the variant form may play a role in incidents of cross-species transmission and emergence of new epidemic variants. Therefore, it is important to investigate how human IAVs interact with Neu5Ac and Neu5Gc. Here, we use membrane platforms that mimic the host cell surface to examine receptor binding and membrane fusion events of human IAV H3N2. Our findings improve the understanding of viral entry mechanisms that can affect host tropism and virus evolution.

Loss of smelling is an early marker of aging and is associated with inflammation and DNA damage in C57BL/6J mice

Olfactory dysfunction is a prevalent symptom and an early marker of age-related neurodegenerative diseases in humans, including Alzheimer's and Parkinson's Diseases. However, as olfactory dysfunction is also a common symptom of normal aging, it is important to identify associated behavioral and mechanistic changes that underlie olfactory dysfunction in nonpathological aging. In the present study, we systematically investigated age-related behavioral changes in four specific domains of olfaction and the molecular basis in C57BL/6J mice. Our results showed that selective loss of odor discrimination was the earliest smelling behavioral change with aging, followed by a decline in odor sensitivity and detection while odor habituation remained in old mice. Compared to behavioral changes related with cognitive and motor functions, smelling loss was among the earliest biomarkers of aging. During aging, metabolites related with oxidative stress, osmolytes, and infection became dysregulated in the olfactory bulb, and G protein coupled receptor-related signaling was significantly down regulated in olfactory bulbs of aged mice. Poly ADP-ribosylation levels, protein expression of DNA damage markers, and inflammation increased significantly in the olfactory bulb of older mice. Lower NAD⁺ levels were also detected. Supplementation of NAD⁺ through NR in water improved longevity and partially enhanced olfaction in aged mice. Our studies provide mechanistic and biological insights into the olfaction decline during aging and highlight the role of NAD⁺ for preserving smelling function and general health.

Intracellular virion traffic to the endosome driven by cell type specific sialic acid receptors determines parvovirus tropism

Parvoviruses are promising anticancer and gene therapy agents, but a deep knowledge of the entry process is crucial to exploit their therapeutic potential. We addressed this issue while attempting to retarget the oncolytic parvovirus minute virus of mice (MVMp) to the tumor vasculature. Residues at three functional domains of the icosahedral capsid were substituted by rational design with peptides competing with the vascular endothelial growth factor. Most substitutions impaired virus maturation, though some yielded infectious chimeric virions, and substitutions in a dimple at the twofold axis that allocates sialic acid (SIA) receptors altered viral tropism. One dimple-modified chimeric virion was efficiently attached as MVMp to α2-linked SIA moieties, but the infection was impaired by the binding to some inhibitory α2-3,-6,-8 SIA pseudoreceptors, which hampers intracellular virus traffic to the endosome in a cell type-dependent manner. Infectious from nonproductive traffic could be mechanistically discriminated by an endosomal drastic capsid structural transition comprising the cleavage of some VP2-Nt sequences and its associated VP1-Nt exposure. Correspondingly, neuraminidase removal of inhibitory SIA moieties enhanced the infection quantitatively, correlating to the restored virus traffic to the endosome and the extent of VP2-Nt cleavage/VP1-Nt exposure. This study illustrates (i) structural constraints to retarget parvoviruses with evolutionary adopted narrow grooves allocating small SIA receptors, (ii) the possibility to enhance parvovirus oncolysis by relaxing the glycan network on the cancer cell surface, and (iii) the major role played by the attachment to cell type-specific SIAs in the intracellular virus traffic to the endosome, which may determine parvovirus tropism and host range.

Multivalent sialic acid materials for biomedical applications

Sialic acid is a kind of monosaccharide expressed on the non-reducing end of glycoproteins or glycolipids. It acts as a signal molecule combining with its natural receptors such as selectins and siglecs (sialic acid-binding immunoglobulin-like lectins) in intercellular interactions like immunological surveillance and leukocyte infiltration. The last few decades have witnessed the exploration of the roles that sialic acid plays in different physiological and pathological processes and the use of sialic acid-modified materials as therapeutics for related diseases like immune dysregulation and virus infection. In this review, we will briefly introduce the biomedical function of sialic acids in organisms and the utilization of multivalent sialic acid materials for targeted drug delivery as well as therapeutic applications including anti-inflammation and anti-virus.

Involvement of sialoglycans in SARS-COV-2 infection: Opportunities and challenges for glyco-based inhibitors

Viral infections have been the causes of global pandemics, including the ongoing coronavirus disease 2019, which prompted the investigation into the infection mechanisms to find treatment and aid the vaccine design. Betacoronaviruses use spike glycoprotein on their surface to bind to host receptors, aiding their host attachment and cell fusion. Protein-glycan interaction has been implicated in the viral entry mechanism of many viruses and has recently been shown in SARS-CoV-2. Here, we reviewed the current knowledge on protein-glycan interactions that facilitate SARS-CoV-2 host entry, with special interest in sialoglycans present on both the virions and host cell surfaces. We also analyze how such information provides opportunities and challenges in glyco-based inhibitors.

In-cell NMR: Why and how?

NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.

Sialic acid: an attractive biomarker with promising biomedical applications

This broad, narrative review highlights the roles of sialic acids as acidic sugars found on cellular membranes. The role of sialic acids in cellular communication and development has been well established. Recently, attention has turned to the fundamental role of sialic acids in many diseases, including viral infections, cardiovascular diseases, neurological disorders, diabetic nephropathy, and malignancies. Sialic acid may be a target for developing new drugs to treat various cancers and inflammatory processes. We recommend the routine measurement of serum sialic acid as a sensitive inflammatory marker in various diseases.

Significant role of host sialylated glycans in the infection and spread of severe acute respiratory syndrome coronavirus 2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been transmitted across all over the world, in contrast to the limited epidemic of genetically- and virologically-related SARS-CoV. However, the molecular basis explaining the difference in the virological characteristics among SARS-CoV-2 and SARS-CoV has been poorly defined. Here we identified that host sialoglycans play a significant role in the efficient spread of SARS-CoV-2 infection, while this was not the case with SARS-CoV. SARS-CoV-2 infection was significantly inhibited by α2-6-linked sialic acid-containing compounds, but not by α2–3 analog, in VeroE6/TMPRSS2 cells. The α2-6-linked compound bound to SARS-CoV-2 spike S1 subunit to competitively inhibit SARS-CoV-2 attachment to cells. Enzymatic removal of cell surface sialic acids impaired the interaction between SARS-CoV-2 spike and angiotensin-converting enzyme 2 (ACE2), and suppressed the efficient spread of SARS-CoV-2 infection over time, in contrast to its least effect on SARS-CoV spread. Our study provides a novel molecular basis of SARS-CoV-2 infection which illustrates the distinctive characteristics from SARS-CoV.

SARS-CoV-2, which has been highly transmissible and rapidly spreading worldwide, has caused approximately 458 million confirmed cases of COVID-19 with more than 6 million deaths by March 2022. Here we found that SARS-CoV-2 infection was significantly inhibited by α2-6-linked sialic acid-containing compounds and by depletion of cell surface sialic acid with only a minor effect on SARS-CoV infection. We identified that SARS-CoV-2 spike S1 subunit directly binds to α2-6-linked sialoglycans for efficient attachment to host cell surface. Our finding indicated that host sialoglycans play a significant role in the efficient infection of SARS-CoV-2, which provides a novel understanding of the molecular basis explaining the rapid spread of SARS-CoV-2 over SARS-CoV.

Synthetic O-Acetyl-N-glycolylneuraminic Acid Oligosaccharides Reveal Host-Associated Binding Patterns of Coronaviral Glycoproteins

A panel of O-acetylated N-glycolylneuraminic acid oligosaccharides has been prepared by diversification of common synthetic precursors by regioselective de-O-acetylation by coronaviral hemagglutinin-esterase (HE) combined with C7-to-C9 acetyl ester migration. The resulting compound library was printed on streptavidin-coated glass slides to give a microarray to investigate receptor binding specificities of viral envelope glycoproteins, including spike proteins and HEs from animal and human coronaviruses. It was found that the binding patterns of the viral proteins for N-glycolylated sialosides differ considerable from those of the previously synthesized N-acetylated counterparts. Generally, the spike proteins tolerate N-glycolyl modification, but selectivities differ among viruses targeting different hosts. On the other hand, the lectin domain of the corresponding HEs showed a substantial decrease or loss of binding of N-glycolylated sialosides. MD simulations indicate that glycolyl recognition by HE is mediated by polar residues in a loop region (109-119) that interacts with the 5-N-glycolyl moiety. Collectively, the results indicate that coronaviruses have adjusted their receptor fine specificities to adapt to the sialoglycome of their host species.

Multivalent 9-O-Acetylated-sialic acid glycoclusters as potent inhibitors for SARS-CoV-2 infection

The recent emergence of highly transmissible SARS-CoV-2 variants illustrates the urgent need to better understand the molecular details of the virus binding to its host cell and to develop anti-viral strategies. While many studies focused on the role of the angiotensin-converting enzyme 2 receptor in the infection, others suggest the important role of cell attachment factors such as glycans. Here, we use atomic force microscopy to study these early binding events with the focus on the role of sialic acids (SA). We show that SARS-CoV-2 binds specifically to 9-O-acetylated-SA with a moderate affinity, supporting its role as an attachment factor during virus landing to cell host surfaces. For therapeutic purposes and based on this finding, we have designed novel blocking molecules with various topologies and carrying a controlled number of SA residues, enhancing affinity through a multivalent effect. Inhibition assays show that the AcSA-derived glycoclusters are potent inhibitors of cell binding and infectivity, offering new perspectives in the treatment of SARS-CoV-2 infection.

Cell surface attachment factors, such as glycans, play an important role in viral infection. Here, Petitjean et al. show that SARS-CoV-2 specifically binds to 9-Oacetylated sialic acid and have designed novel inhibitors based on multivalent derivatives.

Selective Enrichment of Sialylglycopeptides Enabled by Click Chemistry and Dynamic Covalent Exchange

Despite the important roles of protein sialylation in biological processes such as cellular interaction and cancer progression, simple and effective methods for the analysis of intact sialylglycopeptides (SGPs) are still limited. Analyses of low-abundance SGPs typically require efficient enrichment prior to comprehensive liquid chromatography-mass spectrometry (LC-MS)-based analysis. Here, a novel workflow combining mild periodate oxidation, hydrazide chemistry, copper-catalyzed azide/alkyne cycloaddition (CuAAC) click chemistry, and dynamic covalent exchange has been developed for selective enrichment of SGPs. The intact SGPs could be separated easily from protein tryptic digests, and the signature ions were produced during LC-MS/MS for unambiguous identification. The structure of the signature ions and corresponding dynamic covalent exchange were confirmed by using an isotopic reagent. Under the optimized condition, over 70% enrichment efficiency of SGPs was achieved using bovine fetuin digests, and the method was successfully applied to complex biological samples, such as a mouse lung tissue extract. The high enrichment efficiency, good reproducibility, and easily adopted procedure without the need to generate specialized materials make this method a promising tool for broad applications in SGP analysis.

The SARS-CoV-2 Spike Glycoprotein Directly Binds Exogeneous Sialic Acids: A NMR View

The interaction of the SARS CoV2 spike glycoprotein with two sialic acid-containing trisaccharides (α2,3 and α2,6 sialyl N-acetyllactosamine) has been demonstrated by NMR. The NMR-based distinction between the signals of those sialic acids in the glycans covalently attached to the spike protein and those belonging to the exogenous α2,3 and α2,6 sialyl N-acetyllactosamine ligands has been achieved by synthesizing uniformly 13 C-labelled trisaccharides at the sialic acid and galactose moieties. STD-1 H,13 C-HSQC NMR experiments elegantly demonstrate the direct interaction of the sialic acid residues of both trisaccharides with additional participation of the galactose moieties, especially for the α2,3-linked analogue. Additional experiments with the spike protein in the presence of a specific antibody for the N-terminal domain and with the isolated receptor binding and N-terminal domains of the spike protein unambiguously show that the sialic acid binding site is located at the N-terminal domain.

Mucins Inhibit Coronavirus Infection in a Glycan-Dependent Manner

Mucins are a diverse and heterogeneous family of glycoproteins that comprise the bulk of mucus and the epithelial glycocalyx. Mucins are intimately involved in viral transmission. Mucin and virus laden particles can be expelled from the mouth and nose to later infect others. Viruses must also penetrate the mucus layer before cell entry and replication. The role of mucins and their molecular structure have not been well-characterized in coronavirus transmission studies. Laboratory studies predicting high rates of fomite transmission have not translated to real-world infections, and mucins may be one culprit. Here, we probed both surface and direct contact transmission scenarios for their dependence on mucins and their structure. We utilized disease-causing, bovine-derived, human coronavirus OC43. We found that bovine mucins could inhibit the infection of live cells in a concentration- and glycan-dependent manner. The effects were observed in both mock fomite and direct contact transmission experiments and were not dependent upon surface material or time-on-surface. However, the effects were abrogated by removal of the glycans or in a cross-species infection scenario where bovine mucin could not inhibit the infection of a murine coronavirus. Together, our data indicate that the mucin molecular structure plays a complex and important role in host defense.

Glycan-mediated molecular interactions in bacterial pathogenesis

Glycans are expressed on the surface of nearly all host and bacterial cells. Not surprisingly, glycan-mediated molecular interactions play a vital role in bacterial pathogenesis and host responses against pathogens. Glycan-mediated host-pathogen interactions can benefit the pathogen, host, or both. Here, we discuss (i) bacterial glycans that play a critical role in bacterial colonization and/or immune evasion, (ii) host glycans that are utilized by bacteria for pathogenesis, and (iii) bacterial and host glycans involved in immune responses against pathogens. We further discuss (iv) opportunities and challenges for transforming these research findings into more effective antibacterial strategies, and (v) technological advances in glycoscience that have helped to accelerate progress in research. These studies collectively offer valuable insights into new perspectives on antibacterial strategies that may effectively tackle the drug-resistant pathogens that are rapidly spreading globally.

Low molecular weight sulfated chitosan isolation, characterization and anti-tuberculosis activity derived from Sepioteuthis lessoniana

The research focused on tuberculosis as it is one of the world's most serious health problems. The extracted chitin from the gladius of Sepioteuthis lessoniana converted into Chitosan (CH). The purified and freeze-dried CH was refined as Sulfated Chitosan (SCH). The SCH was converted into low molecular weight of SCH with various doses of Gamma Irradiation (GIR). Fluorescence characteristics of GIR-SCH and elemental analysis were confirmed. The structure and molecular weights of GIR-SCH were determined with FT-IR, NMR and MALDI-TOF/Mass Spectroscopy. 100 Gy of GIR-SCH significantly showed the minimum inhibitory concentration (MIC) against Mycobacterium smegmatis. The MIC against M. smegmatis was not affected by the varied sulfate levels in the identical molecular weight GIR-SCH. However, the lowest molecular weight GIR-SCH displayed a significantly MIC against M. smegmatis. In docking analysis, the 6ZT3 ligand had the lowest binding energy of -1.57 kcal/Mol indicating a superior binding interaction with GIR-SCH. The effect of molecular weight reduction by GIR on the anti-tuberculosis capacity of GIR SCH was investigated in this study which had antimicrobial implications.

Synthetic O-Acetylated Sialosides and their Acetamido-deoxy Analogues as Probes for Coronaviral Hemagglutinin-esterase Recognition

O-Acetylation is a common modification of sialic acids that can occur at carbons 4-, 7-, 8-, and/or 9. Acetylated sialosides are employed as receptors by several betacoronaviruses and toroviruses, and by influenza C and D viruses. The molecular basis by which these viruses recognize specific O-acetylated sialosides is poorly understood, and it is unknown how viruses have evolved to recognize specific O-acetylated sialosides expressed by their host. Here, we describe a chemoenzymatic approach that can readily provide sialoglycan analogues in which acetyl esters at C4 and/or C7 are replaced by stabilizing acetamide moieties. The analogues and their natural counterparts were used to examine the ligand requirements of the lectin domain of coronaviral hemagglutinin-esterases (HEs). It revealed that HEs from viruses targeting different host species exhibit different requirements for O-acetylation. It also showed that ester-to-amide perturbation results in decreased or loss of binding. STD NMR and molecular modeling of the complexes of the HE of BCoV with the acetamido analogues and natural counterparts revealed that binding is governed by the complementarity between the acetyl moieties of the sialosides and the hydrophobic patches of the lectin. The precise spatial arrangement of these elements is important, and an ester-to-amide perturbation results in substantial loss of binding. Molecular Dynamics simulations with HEs from coronaviruses infecting other species indicate that these viruses have adapted their HE specificity by the incorporation of hydrophobic or hydrophilic elements to modulate acetyl ester recognition.

Investigation on the Binding Properties of N1 Neuraminidase of H5N1 Influenza Virus in Complex with Fluorinated Sialic Acid Analog Compounds—a Study by Molecular Docking and Molecular Dynamics Simulations

Worldwide, only two types of antiviral inhibitors (M2 ion channel protein inhibitor and Neuraminidase inhibitors) are approved to treat the influenza viral infection. But the mutation of amino acid sequence in the viral membrane proteins creates the viral resistance to existing antiviral drugs or inhibitors. So the corresponding antiviral drugs have to be reformulated to match these antigenic variations. Fluorination on the carbon–based molecule significantly enriches its biological properties. Hence this study is motivated to design the fluorinated sialic acid (SIA) analog inhibitors for the neuraminidase of H5N1 influenza A virus by substituting fluorine atom at different hydroxyls (O2, O4, O7, O8, and O9) of sialic acid. 100 ns molecular dynamics simulations are carried out for each protein–ligand complex system. NAMD pair interaction energy and MM–PBSA binding free energy calculations predict two possible binding modes for N1–SIA_F2, N1–SIA_F4, and N1–SIA_F7 complexes and single binding mode for N1–SIA_F8 and N1–SIA_F9 complexes. RMSD, RMSF, and hydrogen bonding analyses are used to understand the conformational flexibility and structural stability of each complex system. It has been concluded that the fluorinated sialic acid drug candidates SIA_F2 and SIA_F7 have better inhibiting potency against the N1 neuraminidase of H5N1 influenza virus.

Evolution of influenza A virus in intensive and free-range swine farms in Spain

Swine harbor genetically diverse influenza A viruses (IAVs) with the capacity to host-switch to humans, causing global pandemics. Spain is the largest swine producer in Europe and has a mixed production system that includes 'white coat' pigs raised intensively in modern buildings and free-range Iberian pigs that interface differently with humans, wildlife, and other swine. Through active longitudinal IAV surveillance in nine Spanish provinces during 2015-9, we generated forty-seven complete or near-complete genome sequences from IAVs collected from swine in both systems. Genetically diverse IAVs were identified in intensively raised white pigs and free-range Iberian pigs, including new H3N1 reassortants. Both systems are dynamic environments for IAV evolution, but driven by different processes. IAVs in white pigs were genetically related to viruses found in swine raised intensively in other European countries, reflecting high rates of viral introduction following European trade routes. In contrast, IAVs in Iberian pigs have a genetic makeup shaped by frequent introductions of human IAVs, reflecting rearing practices with high rates of human contact. Transmission between white and Iberian pigs also occurred. In conclusion, Iberian swine with high rates of human contact harbor genetically diverse IAVs and potentially serve as intermediary hosts between white pigs and humans, presenting an understudied zoonotic risk that requires further investigation.

Glycomics reveal that ST6GAL1-mediated sialylation regulates uterine lumen closure during implantation

Objectives

Implantation failure is a major cause of prenatal mortality. The uterine lumen closure contributes to embryo adhesion to the uterus, but its underlying mechanisms are largely unknown. Our previous study has reported that endometrial fold extension can lead to uterine lumen closure in pigs. The objective of this study was to reveal molecular mechanisms of the uterine lumen closure by characterizing the molecular basis of the endometrial fold extension during implantation in pigs.

Materials and methods

Uterine and endometrium tissues during implantation were collected in pigs. MALDI‐TOF MS was used to characterize the N‐glycomic profiles. Histochemistry, siRNA transfection, Western blotting, lectin immumoprecipitation, mass spectrometry and assays of wounding healing and cell aggregation were performed to investigate the molecular basis.

Results

We observed that uterine luminal epithelium (LE) migrated collectively during endometrial fold extension. For the first time, we identified a large number of N‐glycan compositions from endometrium during implantation using MALDI‐TOF MS. Notably, the α2,6‐linked sialic acid and ST6GAL1 were highly expressed in uterine LE when the endometrial folds extended greatly. Subsequently, the role of ST6GAL1‐mediated 2,6‐sialylation in collective epithelial migration was demonstrated. Finally, we found that ST6GAL1‐mediated α2,6‐sialylation of E‐cadherin may participate in collective migration of uterine LE.

Conclusions

The study reveals a mechanism of uterine lumen closure by identifying that ST6GAL1‐mediated α2,6‐sialylation of cell adhesion molecules contributes to endometrial fold extension through regulating collective migration of uterine LE.

Glycosylation of SARS-CoV-2: structural and functional insights

The COVID-19 pandemic is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Similar to other coronaviruses, its particles are composed of four structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins. S, E, and M proteins are glycosylated, and the N protein is phosphorylated. The S protein is involved in the interaction with the host receptor human angiotensin-converting enzyme 2 (hACE2), which is also heavily glycosylated. Recent studies have revealed several other potential host receptors or factors that can increase or modulate the SARS-CoV-2 infection. Interestingly, most of these molecules bear carbohydrate residues. While glycans acquired by the viruses through the hijacking of the host machinery help the viruses in their infectivity, they also play roles in immune evasion or modulation. Glycans play complex roles in viral pathobiology, both on their own and in association with carrier biomolecules, such as proteins or glycosaminoglycans (GAGs). Understanding these roles in detail can help in developing suitable strategies for prevention and therapy of COVID-19. In this review, we sought to emphasize the interplay of SARS-CoV-2 glycosylated proteins and their host receptors in viral attachment, entry, replication, and infection. Moreover, the implications for future therapeutic interventions targeting these glycosylated biomolecules are also discussed in detail.

In silico exploration of enzymes involved in sialic acid biosynthesis and their possible role in SARS-CoV-2 infection

Salivary glands are considered important targets of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Recent evidence suggests that along with angiotensin converting enzyme 2, certain cell surface sialic acids (Sia) may function as receptors for binding SARS-CoV-2 spike protein. Over 50 forms of Sia have been identified in nature, with N-acetylneuraminic acid (Neu5Ac) being the most abundant. We explored the Human Protein Atlas repository to analyze important enzymes in Neu5Ac biosynthesis and propose a hypothesis that further highlights the significance of salivary glands in coronavirus disease 19 (COVID-19). This work may facilitate research into targeted drug therapies for COVID-19.

The role of cell surface sialic acids for SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a new virus that has higher contagious capacity than any other previous human coronaviruses (HCoVs) and causes the current coronavirus disease 2019 pandemic. Sialic acids are a group of nine-carbon acidic α-keto sugars, usually located at the end of glycans of cell surface glycoconjugates and serve as attachment sites for previous HCoVs. It is therefore speculated that sialic acids on the host cell surface could serve as co-receptors or attachment factors for SARS-CoV-2 cell entry as well. Recent in silico modeling, molecular modeling predictions and microscopy studies indicate potential sialic acid binding by SARS-CoV-2 upon cell entry. In particular, a flat sialic acid-binding domain was proposed at the N-terminal domain of the spike protein, which may lead to the initial contact and interaction of the virus on the epithelium followed by higher affinity binding to angiotensin-converting enzyme 2 (ACE2) receptor, likely a two-step attachment fashion. However, recent in vitro and ex vivo studies of sialic acids on ACE2 receptor confirmed an opposite role for SARS-CoV-2 binding. In particular, neuraminidase treatment of epithelial cells and ACE2-expressing 293T cells increased SARS-CoV-2 binding. Furthermore, the ACE2 glycosylation inhibition studies indicate that sialic acids on ACE2 receptor prevent ACE2-spike protein interaction. On the other hand, a most recent study indicates that gangliosides could serve as ligands for receptor-binding domain of SARS-CoV-2 spike protein. This mini-review discusses what has been predicted and known so far about the role of sialic acid for SARS-CoV-2 infection and future research perspective.