Sialic Acid Binding Research Articles

Virion-associated influenza hemagglutinin clusters upon sialic acid binding visualized by cryo-electron tomography.

Influenza viruses are enveloped, negative sense single-stranded RNA viruses covered in a dense layer of glycoproteins. Hemagglutinin (HA) accounts for 80-90% of influenza glycoprotein and plays a role in host cell binding and membrane fusion. While previous studies have characterized structures of receptor-free and receptor-bound HA in vitro, the effect of receptor binding on HA organization and structure on virions remains unknown. Here, we used cryo-electron tomography (cryoET) to visualize influenza virions bound to a sialic acid receptor mimic. Overall, receptor binding did not result in significant changes in viral morphology; however, we observed rearrangements of HA trimer organization and orientation. Compared to the even inter-glycoprotein spacing of unliganded HA trimers, receptor binding promotes HA trimer clustering and formation of a triplet of trimers. Subtomogram averaging and refinement yielded 8-10 Å reconstructions that allowed us to visualize specific contacts between HAs from neighboring trimers and identify molecular features that mediate clustering. Taken together, we present new structural evidence that receptor binding triggers clustering of HA trimers, revealing an additional layer of HA dynamics and plasticity.

On the function of TRAP substrate-binding proteins: Conformational variation of the sialic acid binding protein SiaP

Tripartite ATP-independent periplasmic (TRAP) transporters are analogous to ABC transporters in that they use a substrate-binding protein to scavenge metabolites (e.g., N-acetylneuraminate) and deliver them to the membrane components for import. TRAP substrate-binding proteins are thought to bind the substrate using a two-state (open and closed) induced-fit mechanism. We solved the structure of the TRAP N-acetylneuraminate substrate-binding protein from Aggregatibacter actinomycetemcomitans (AaSiaP) in both the open ligand-free and closed liganded conformations. Surprisingly, we also observed an intermediate conformation, where AaSiaP is mostly closed and is bound to a non-cognate ligand, acetate, which hints at how N-acetylneuraminate binding stabilises a fully closed state. AaSiaP preferentially binds N-acetylneuraminate (KD = 0.4 μM) compared to N-glycolylneuraminate (KD = 4.4 μM), which is explained by the closed-N-acetylneuraminate bound structure. Small-angle X-ray scattering data alongside molecular dynamics simulations suggest the AaSiaP adopts a more open state in solution than in crystal. However, the open unliganded conformation can also sample closed conformations. Molecular dynamics simulations also demonstrate the importance of water molecules for stabilising the closed conformation. Although our data is consistent with an induced fit model of binding, we suggest that the open unliganded conformation may sample multiple states capable of binding substrate. The mechanism by which the ligand is released for import remains to be determined.

CD33 and SHP-1/PTPN6 Interaction in Alzheimer's Disease.

Large-scale genetic studies have identified numerous genetic risk factors that suggest a central role for innate immune cells in susceptibility to Alzheimer's disease (AD). CD33, an immunomodulatory transmembrane sialic acid binding protein expressed on myeloid cells, was identified as one such genetic risk factor associated with Alzheimer's disease. Several studies explored the molecular outcomes of genetic variation at the CD33 locus. It has been determined that the risk variant associated with AD increases the expression of the large isoform of CD33 (CD33M) in innate immune cells and alters its biological functions. CD33 is thought to signal via the interaction of its ITIM motif and the protein tyrosine phosphatase, SHP-1. Here, we utilize different molecular and computational approaches to investigate how AD-associated genetic variation in CD33 affects its interaction with SHP-1 in human microglia and microglia-like cells. Our findings demonstrate a genotype-dependent interaction between CD33 and SHP-1, which may functionally contribute to the AD risk associated with this CD33 variant. We also found that CD33-PTPN6 (SHP-1) gene-gene interactions impact AD-related traits, while CD33-PTPN11 (SHP-2) interactions do not.

A Novel Electrochemiluminescence (ECL) Immunoassay for Detection of Anti-drug Antibodies (ADAs) to a Monoclonal Antibody (mAb) PYX-106 in Human Serum

Background: PYX-106 is a fully human monoclonal antibody (mAb), targeting sialic acid binding immunoglobulin-like lectin-15 (Siglec-15), an immunosuppressive agent with widespread expression across various tumor types. Methods: To facilitate the evaluation of immunogenicity for PYX-106 in human serum, a validated method was established to enable the detection (screening, confirmatory, and titration) of antibodies to PYX-106 in human serum samples. Results: The Screening Cut-Point Factor (SCPF), Confirmatory Cut-Point (CCP), and Titration Cut-Point Factor (TCPF) were found to be 1.51, 26.9%, and 1.86, respectively. Sensitivity was determined to be 1.81 ng/mL in the screening assay and 1.25 ng/mL in the confirmatory assay. Low Positive Control (LPC) was set at 6.00 ng/mL, and High Positive Control (HPC) was set at 1000 ng/mL. The drug tolerance was up to 500 μg/mL at the HPC level, up to 241 μg/mL at the ADA 100 ng/mL level, and up to 38.9 μg/mL at the LPC level. The intra-assay percent coefficient of variation (%CV) was ≤ 2.1% for Positive Controls (PCs) in the screening assay and ≤ 1.0% for PCs in the confirmatory assay. The inter-assay %CV was ≤ 15.3% for PCs in the screening assay and ≤ 2.1% for PCs in the confirmatory assay. No hook effect, hemolysis effect, lipemia effect, or bilirubin interference was found in this ADA method. Anti-PYX-106 antibodies were found stable in human serum for at least 23 hours 51 minutes at room temperature or after six freeze/thaw cycles. Conclusion: Anti-PYX-106 ADA, bioanalytical assay validation, was reported for the first time in any biological matrix. This ADA method has been successfully applied to human sample analysis to support a clinical study.

Structural Characterization of Human Bufavirus 1: Receptor Binding and Endosomal pH-Induced Changes.

Bufaviruses (BuV) are members of the Parvoviridae of the Protoparvovirus genus. They are non-enveloped, T = 1 icosahedral ssDNA viruses isolated from patients exhibiting acute diarrhea. The lack of treatment options and a limited understanding of their disease mechanisms require studying these viruses on a molecular and structural level. In the present study, we utilize glycan arrays and cell binding assays to demonstrate that BuV1 capsid binds terminal sialic acid (SIA) glycans. Furthermore, using cryo-electron microscopy (cryo-EM), SIA is shown to bind on the 2/5-fold wall of the capsid surface. Interestingly, the capsid residues stabilizing SIA binding are conserved in all human BuVs identified to date. Additionally, biophysical assays illustrate BuV1 capsid stabilization during endo-lysosomal (pH 7.4-pH 4) trafficking and capsid destabilization at pH 3 and less, which correspond to the pH of the stomach. Hence, we determined the cryo-EM structures of BuV1 capsids at pH 7.4, 4.0, and 2.6 to 2.8 Å, 3.2 Å, and 2.7 Å, respectively. These structures reveal capsid structural rearrangements during endo-lysosomal escape and provide a potential mechanism for this process. The structural insights gained from this study will add to the general knowledge of human pathogenic parvoviruses. Furthermore, the identification of the conserved SIA receptor binding site among BuVs provides a possible targetable surface-accessible pocket for the design of small molecules to be developed as anti-virals for these viruses.

Single-molecule imaging reveals allosteric stimulation of SARS-CoV-2 spike receptor binding domain by host sialic acid.

Conformational dynamics of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein (S) mediate exposure of the binding site for the cellular receptor, angiotensin-converting enzyme 2 (ACE2). The N-terminal domain (NTD) of S binds terminal sialic acid (SA) moieties on the cell surface, but the functional role of this interaction in virus entry is unknown. Here, we report that NTD-SA interaction enhances both S-mediated virus attachment and ACE2 binding. Through single-molecule Förster resonance energy transfer imaging of individual S trimers, we demonstrate that SA binding to the NTD allosterically shifts the S conformational equilibrium, favoring enhanced exposure of the ACE2-binding site. Antibodies that target the NTD block SA binding, which contributes to their mechanism of neutralization. These findings inform on mechanisms of S activation at the cell surface.

A Siglec3-like lectin from Nile tilapia (Oreochromis niloticus): Transcriptional profiling upon Streptococcus agalactiae infection and its potential role in immune escape

Siglec-3, also known as CD33, is a type of sialic acid binding immunoglobulin-like lectin that plays a role in regulating cellular activation in the innate immune system and subsequent inflammatory responses. In this study, we cloned the cDNA encoding OnSiglec3-like ORF sequence (1170 bp) in Nile tilapia, contained two Ig-like domains in the extracellular region and one inhibitory ITIM-like motif in the intracellular region. Through qRT-PCR analysis, we found that the mRNA of OnSiglec3-like lectin was highly expressed in the brain and head kidney. When challenged with Streptococcus agalactiae both in vivo and in vitro, we observed a significant up-regulation in the expression of OnSiglec3-like lectin in the head kidney tissues and leukocytes, respectively. Additionally, we investigated the interaction between a recombinant extracellular region protein (referred to as (r)exSiglec3-like protein) and three different phenotypes of S. agalactiae: WT (wild type), ∆cps (cps-deficient mutant), and ∆neuA (sia-deficient mutant) using ELISA. We found that the exOnSiglec3-like protein, when combined with RNA interference and bacterial infection, significantly enhanced the phagocytic ability against S. agalactiae. Furthermore, the expression of four common inflammatory factors (OnIL-6, OnIL-10, OnTNF-α, and OnTGF-β) showed a significant up-regulation. Overall, this study suggests that OnSigelc3-like lectin may play a role in host defence against bacterial infection and mediate immune escape in Nile tilapia.

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.

Structural and functional characterization of avian influenza H9N2 virus neuraminidase with a combination of five novel mutations

The influenza virus neuraminidase (NA) protein is responsible for actively cleaving the sialic acid (SA) bound to the viral hemagglutinin. In the present study, we identified a combination of five novel amino acid substitutions in the NA, conferring increased substrate binding and altered surface characteristics to a low pathogenic avian influenza (LPAI) H9N2 virus strain. The H9N2 strain reported from India, A/Environmental/India/1726265/2017 (H9N2-1726265) showed the combination of amino acid substitutions T149I, R249W, G346A, W403R and G435R, which were in the vicinity of the enzyme active site cavity. The strain A/chicken/India/99321/2009 (H9N2-99321) did not show these substitutions and was used for comparison. Virus elution was studied using turkey red blood cells (tRBCs). NA enzyme kinetics assays were carried out using the MUNANA substrate, which is an SA analogue. Homology modelling and molecular docking were performed to determine alterations in the surface characteristics and substrate binding. H9N2-1726265 showed enhanced elution from tRBCs. Enzyme kinetics revealed a lower KM of H9N2-1726265 (111.5 μM) as compared to H9N2-99321 (135.2 μM), indicating higher substrate binding affinity of H9N2-1726265, due to which the NA enzyme cleaved the SA more efficiently, leading to faster elution. Molecular docking revealed a greater number of binding interactions of H9N2-1726265 to SA as compared to H9N2-99321 corroborating the greater substrate binding affinity. Changes in the surface charge, hydrophobicity, and contour, were observed in H9N2-1726265 NA due to the five substitutions. Thus, the novel combination of five amino acids near the sialic acid binding site of NA, resulted in altered surface characteristics, higher substrate binding affinity, and virus elution.

Functional dissection of the spike glycoprotein S1 subunit and identification of cellular cofactors for regulation of swine acute diarrhea syndrome coronavirus entry.

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a novel porcine enteric coronavirus, and the broad interspecies infection of SADS-CoV poses a potential threat to human health. This study provides experimental evidence to dissect the roles of distinct domains within the SADS-CoV spike S1 subunit in cellular entry. Specifically, we expressed the S1 and its subdomains, S1A and S1B. Cell binding and invasion inhibition assays revealed a preference for the S1B subdomain in binding to the receptors on the cell surface, and this unknown receptor is not utilized by the porcine epidemic diarrhea virus. Nanoparticle display demonstrated hemagglutination of erythrocytes from pigs, humans, and mice, linking the S1A subdomain to the binding of sialic acid (Sia) involved in virus attachment. We successfully rescued GFP-labeled SADS-CoV (rSADS-GFP) from a recombinant cDNA clone to track viral infection. Antisera raised against S1, S1A, or S1B contained highly potent neutralizing antibodies, with anti-S1B showing better efficiency in neutralizing rSADS-GFP infection compared to anti-S1A. Furthermore, depletion of heparan sulfate (HS) by heparinase treatment or pre-incubation of rSADS-GFP with HS or constituent monosaccharides could inhibit SADS-CoV entry. Finally, we demonstrated that active furin cleavage of S glycoprotein and the presence of type II transmembrane serine protease (TMPRSS2) are essential for SADS-CoV infection. These combined observations suggest that the wide cell tropism of SADS-CoV may be related to the distribution of Sia or HS on the cell surface, whereas the S1B contains the main protein receptor binding site. Specific host proteases also play important roles in facilitating SADS-CoV entry.IMPORTANCESwine acute diarrhea syndrome coronavirus (SADS-CoV) is a novel pathogen infecting piglet, and its unique genetic evolution characteristics and broad species tropism suggest the potential for cross-species transmission. The virus enters cells through its spike (S) glycoprotein. In this study, we identify the receptor binding domain on the C-terminal part of the S1 subunit (S1B) of SADS-CoV, whereas the sugar-binding domain located at the S1 N-terminal part of S1 (S1A). Sialic acid, heparan sulfate, and specific host proteases play essential roles in viral attachment and entry. The dissection of SADS-CoV S1 subunit's functional domains and identification of cellular entry cofactors will help to explore the receptors used by SADS-CoV, which may contribute to exploring the mechanisms behind cross-species transmission and host tropism.

Identification of BACH1-IT2-miR-4786-Siglec-15 immune suppressive axis in bladder cancer

The sialic acid binding Ig like lectin 15 (Siglec-15) was previously identified as tumor immune suppressor gene in some human cancers with elusive molecular mechanism to be elucidated. The continuous focus on both clinical and basic biology of bladder cancer leads us to characterize aberrant abundance of BACH1-IT2 associating with stabilization of Siglec-15, which eventually contributes to local immune suppressive microenvironment and therefore tumor advance. This effect was evidently mediated by miR-4786-5p. BACH1-IT2 functions in this scenario as microRNA sponge, and competitively conceals miR-4786 and up-regulates cancer cell surface Siglec-15. The BACH1-IT2-miR-4786-Siglec-15 axis significantly influences activation of immune cell co-culture. In summary, our data highlights the critical involvements of BACH1-IT2 and miR-4786 in immune evasion in bladder cancer, which hints the potential for both therapeutic and prognostic exploitation.

Wild Bird-Origin H6N2 Influenza Virus Acquires Enhanced Pathogenicity after Single Passage in Mice.

The H6 subtype of avian influenza viruses (AIVs) has emerged as one of the predominant subtypes in both wild and domestic avian species. Currently, H6 AIVs have acquired the ability to infect a wide range of mammals, though the related molecular mechanisms have yet to be fully investigated. In this study, a wild bird-origin H6N2 AIV was isolated from the East Asian-Australasian migratory flyway region located in Liaoning Province. This H6N2 virus initially expressed limited replication in mice. However, after one passage in mice, the virus acquired two mutations, PB2 E627K and HA A110V. The mutant displayed enhanced replication both in vitro and in vivo, proving lethal to mice. But the mutant retained the α-2, 3-linked sialic acid binding property and failed to transmit in guinea pigs. We explored the molecular mechanisms underlying the pathogenicity difference between the wild type and the mutant. Our findings revealed that PB2 E627K dramatically enhanced the polymerase activity of the H6N2 virus, while the HA A110V mutation decreased the pH of HA activation. This study demonstrated that the H6N2 subtype wild bird-origin AIV easily acquired the mammalian adaptation. The monitoring and evaluation of H6 wild bird-origin AIV should be strengthened.

Unraveling Molecular Recognition of Glycan Ligands by Siglec-9 via NMR Spectroscopy and Molecular Dynamics Modeling.

Human sialic-acid-binding immunoglobulin-like lectin-9 (Siglec-9) is a glycoimmune checkpoint receptor expressed on several immune cells. Binding of Siglec-9 to sialic acid containing glycans (sialoglycans) is well documented to modulate its functions as an inhibitory receptor. Here, we first assigned the amino acid backbone of the Siglec-9 V-set domain (Siglec-9d1), using well-established triple resonance three-dimensional nuclear magnetic resonance (NMR) methods. Then, we combined solution NMR and molecular dynamic simulation methods to decipher the molecular details of the interaction of Siglec-9 with the natural ligands α2,3 and α2,6 sialyl lactosamines (SLN), sialyl Lewis X (sLeX), and 6-O sulfated sLeX and with two synthetically modified sialoglycans that bind with high affinity. As expected, Neu5Ac is accommodated between the F and G β-strands at the canonical sialic acid binding site. Addition of a heteroaromatic scaffold 9N-5-(2-methylthiazol-4-yl)thiophene sulfonamide (MTTS) at the C9 position of Neu5Ac generates new interactions with the hydrophobic residues located at the G-G' loop and the N-terminal region of Siglec-9. Similarly, the addition of the aromatic substituent (5-N-(1-benzhydryl-1H-1,2,3-triazol-4-yl)methyl (BTC)) at the C5 position of Neu5Ac stabilizes the conformation of the long and flexible B'-C loop present in Siglec-9. These results expose the underlying mechanism responsible for the enhanced affinity and specificity for Siglec-9 for these two modified sialoglycans and sheds light on the rational design of the next generation of modified sialoglycans targeting Siglec-9.

Molecular docking screening, dynamics simulations, ADMET, and semi-synthesis prediction of flavones and flavonols from the COCONUT database as potent bifunctional neuraminidase inhibitors

Finding new neuraminidase (N) inhibitors to improve anti-influenza treatment is necessary because of the high mutation rates of N protein. Over 3,000 flavones/flavonols and their synthesized products from the COCONUT database were performed in silico docking screening with N1-H274Y-oseltamivir protein (PDB ID: 3CL0). Several derivatives containing nitrogen heterocyclic groups or aromatic rings showed higher anti-neuraminidase potential than that of laninamivir. Especially, the linker groups between the flavone aglycone and nitrogen heterocyclic group created the interactions with the triad of arginine residues Arg118-Arg292-Arg371, which suggested these compounds could become bifunctional inhibitors against the influenza virus strains at the sialic acid binding site and the adjacent 430-cavity position through triad of arginine residues binding. ADMET indicators and the synthesis design strategy of the most suitable compound, ethyl 4-{2-[(5-hydroxy-4-oxo-2-phenyl-4H-chromen-7-yl)oxy]acetyl}piperazine-1-carboxylate, were also successfully predicted and it could be a concerned candidate for further wet-lab synthesis, in vivo and clinical study.

The immunopathogenesis of Helicobacter pylori-induced gastric cancer: a narrative review.

Helicobacter pylori infection is a well-established risk factor for the development of gastric cancer (GC). Understanding the immunopathogenesis underlying this association is crucial for developing effective preventive and therapeutic strategies. This narrative review comprehensively explores the immunopathogenesis of H. pylori-induced GC by delving into several key aspects, emphasizing the pivotal roles played by H. pylori virulence factors, including cytotoxin-associated gene A (cagA) and vacuolating cytotoxin A (vacA), blood group antigen-binding adhesin (babA), and sialic acid binding adhesin (sabA). Moreover, the review focuses on the role of toll-like receptors (TLRs) and cytokines in the complex interplay between chronic infection and gastric carcinogenesis. Finally, the study examines the association between H. pylori evasion of the innate and adaptive immune response and development of GC. A comprehensive understanding of the immunopathogenesis of H. pylori-induced GC is essential for designing targeted interventions to prevent and manage this disease. Further research is warranted to elucidate the intricate immune responses involved and identify potential therapeutic targets to improve patient outcomes.

The identification of a PTEN-associated gene signature for the prediction of prognosis and planning of therapeutic strategy in endometrial cancer.

Endometrial cancer (EC) is one of the most common malignancies among women. To improve the prognosis and treatment of EC, finding out a phosphatase and tensin homolog deleted on chromosome 10 (PTEN)-associated prognostic signature would be beneficial. EC clinical data, genetic mutation data, and transcriptome data were downloaded from The Cancer Genome Atlas (TCGA) database. To clarify the specific PTEN-associated signature, cox regression analyses were performed. The clinical value of the selected signature on the overall survival (OS) and the secretoglobin family 2A member 1 (SCGB2A1)-independent analysis, immune and functional analysis were investigated respectively. Five hundred and fourteen EC samples were screened and PTEN mutation occupied 57%. Enrichment analysis indicated that mutant-type PTEN was enriched for pathways related to the upregulated human T-cell leukemia virus-1 (HTLV-1) infection and estrogen signaling pathway. SCGB2A1 was identified by cox regression analysis. Immune analysis exhibited significant immune infiltration with higher expression of T cells, B cells, and macrophage groups. Immune-checkpoint transcripts CD274 molecule (CD274), and cytotoxic T-lymphocyte associated protein 4 (CTLA4), hepatitis A virus cellular receptor 2 (HAVCR2), lymphocyte activation gene 3 (LAG3), programmed cell death 1 (PDCD1), PDCD1 ligand 2 (PDCD1LG2), T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibition motif domains (TIGIT), and sialic acid binding immunoglobulin like lectin 15 (SIGLEC15) were discovered statistically different. In addition, the low-SCGB2A1 group had worse OS than the high-SCGB2A1 group. SCGB2A1 showed significant area under the curve (AUC) values in a time-dependent receiver operating characteristic (ROC) analysis. Prevalence of microsatellite instability (MSI) was detected and SCGB2A1 showed a negative correlation with EC. Immune checkpoint blockade (ICB) response indicated a worse immune response in the low-SCGB2A1 group. The distribution of one-class linear regression (OCLR) scores reflected the negative correlation between messenger RNA expression-based stemness index (mRNAsi) and prognostic gene expression. Furthermore, several SCGB2A1-related signaling pathways in EC were identified. SCGB2A1 is a prognostic immunometabolic signature for patients with EC, which may help improve the prognosis and therapeutic effect.

The Immune Checkpoint Siglec-15 in Promoting Immune Dysregulation in Non-Hodgkin's Lymphomas

Outcomes for patients with relapsed or refractory (r/r) hematologic malignancies remain dismal despite therapeutic advances over the last several years. This is particularly striking in patients with r/r aggressive mature B-cell lymphomas such as Diffuse Large B-cell Lymphoma (DLBCL) and Burkitt's Lymphoma (BL). With use of intensive multiagent chemo-immunotherapy, DLBCL, which accounts for approximately 10-20% of pediatric Non-Hodgkin's Lymphoma (NHL) cases and is the most common subtype in adults, is highly curable with 5-year event free survival >75%. However, approximately 30-40% of adults diagnosed with DLBCL will become refractory to or relapse after first-line treatment. Yet even with intensive salvage regimens, r/r DLBCL remains a clinical challenge. There remains an unmet need to identify specific defects in the immune response, among other pathways, that drive lymphomagenesis that will in turn inform the development of novel therapeutics to improve survival in this population of patients. Siglec-15 (Sig-15), a member of the sialic acid binding immunoglobulin-like lectin family of proteins, has recently been identified as a critical immune suppressor that is highly expressed in human cancers and intra-tumoral myeloid cells. Importantly, recent reports have demonstrated inhibition of Sig-15, has a restorative effect on local anti-tumor immune responses and abrogated tumor progression. While reported in solid malignancies and acute leukemias, a role for Siglec-15 in promoting disease progression in aggressive B-cell lymphomas has not yet been described. We have found higher expression of SIGLEC15 in DLBCL cell lines compared to normal B cells at the RNA level, through analyses of the publicly available ONCOMINE database. This was confirmed at the protein level by western blot demonstrating higher Sig-15 expression in various lymphoma cell lines (RAJI, SUDHL6, OCI-LY10, HBL-1) compared to healthy donor PBMCs. Further, immunohistochemistry evaluating Sig-15 expression was performed on a tumor microarray consisting of 139 cases of DLBCL from adult patients along with validation samples from 15 primary pediatric lymphoma cases (DLBCL, BL and Anaplastic Large Cell Lymphoma (ALCL)). Sig-15 was found to be highly expressed, with histologic scores ranging from weak (1+) to strong (3+) in 124 out of the 139 adult cases (Figure 1A) and in all pediatric lymphoma samples but with distinct staining patterns observed in the aggressive B-cell lymphomas. Specifically, Sig-15 appears to be highly expressed and associated with the cell membrane in most DLBCL and Burkitt's lymphoma. Expression is more variable in ALCL, primarily elevated in the cytoplasm at low levels and/or in macrophages (Figure 1A). There is heterogeneity in Sig-15 expression with preliminary analysis of RNA-seq data from a cohort of 693 DLBCL patient samples demonstrates higher levels in the germinal center B-cell (GCB) versus activated B-cell molecular (ABC) subtype of DLBCL when compared to healthy controls (Kruskal-Wallis, *p = 0.041). Finally, using a well-established murine lymphoma model, A20 cells were stably transduced with control, non-silencing shRNA (shNS) or shRNA against Sig-15 and injected into un-irradiated immune competent (wild type, WT) or immune deficient ( Rag1 -/-) BALB/C mice and monitored for signs of lymphoma development. Knockdown of Sig-15 in A20 cells abrogates disease progression in WT but not immune deficient mice (Log-rank, **p <0.0001, n=10 mice/group), consistent with a role for Sig-15 in immune evasion in lymphoma (Figure 1B). Together, these data implicate Sig-15 as an immune checkpoint that may be inhibited therapeutically to promote an immune response to lymphoma cells.

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.

Identification of Aztreonam as a potential antibacterial agent against Pasteurella multocida sialic acid binding protein: A combined in silico and in-vitro analysis

Pasteurella multocida, a Gram-negative zoonotic bacterial pathogen, interacts with the host environment, immune response, and infection through outer membrane proteins, adhesins, and sialic acid binding proteins. Sialic acids provide nutrition and mask bacterial identity, hindering the complement system, facilitates tissue access and biofilm formation. Sialic acid binding protein (SAB) enable adhesion to host cells, immune evasion, and nutrient acquisition, making them potential targets for preventing Pasteurella multocida infections. In this study, in silico molecular docking assessed 11 antibiotics targeting SAB (4MMP) comparing their docking scores to Amoxicillin. As SAB (4MMP) exhibits a highly conserved sequence in various Pasteurella multocida strains, including the specific strain PMR212 studied in this article, with a 96.09% similarity score. Aztreonam and Gentamicin displayed the highest docking scores (−6.025 and −5.718), followed by a 100ns molecular dynamics simulation. Aztreonam exhibited stable simulation with protein RMSD fluctuations of 1.8–2.2 Å. The ligand initially had an RMSD of 1.6 Å, stabilizing at 4.8 Å. Antibiotic sensitivity testing confirmed Aztreonam's efficacy with the largest inhibition zone of 42 mm, while Amoxicillin and Gentamicin had inhibition zones of 32 mm and 25 mm, respectively. According to CLSI guidelines, all three antibiotics were effective against Pasteurella multocida. Aztreonam's superior efficacy positions it as a promising candidate for further investigation in targeting Pasteurella multocida.

The Contribution of Serum Sialic Acid Binding Immunoglobulin-Like Lectin 1(sSIGLEC-1) as an IFN I Signature Biomarker in the Progression of Atherosclerosis in Egyptian Systemic Lupus Erythematosus (SLE) Patients.

Clinical symptoms of systemic lupus erythematosus (SLE), such as atherosclerosis and related cardiovascular diseases, are caused by inflammatory cytokines and endothelial cell damage. The serum sialic acid binding immunoglobulin-like lectin 1 (sSIGLEC-1) is thought to be an alternative biomarker of IFN signature and may have a role in the pathogenesis of atherosclerosis. The aim of the study was to measure the levels of sSIGLEC-1 in the serum of SLE patients in comparison to a control group and examine the associations between sSIGLEC-1, SLEDAI, lipid profile, oxidized low density lipoprotein (oxLDL), and carotid intima media thickness (CIMT) to investigate whether sSIGLEC-1 participates in the development of atherosclerosis. sSIGLEC-1 levels were tested in 53 patients and 20 volunteers using ELISA kit. Duplex measurements were performed on all subjects to measure CIMT. SLE patients had significantly higher values of sSIGLEC-1 (P < 0.0001), total cholesterol (P = 0.029), triglycerides (P = 0.001), low density lipoprotein (P = 0.032), oxLDL (P = 0.001), right CIMT (P = 0.0099) and a significantly lower value of high-density lipoprotein (P = 0.04) when compared to controls. sSIGLEC-1 had significant positive correlations with right CIMT (r = 0.5, P < 0.0002) and oxLDL (r = 0.67, P < 0.0001) in all SLE patients. When compared to non-dyslipidemic patients, the dyslipidemic group exhibited significantly higher levels of all previous parameters except HDL and left CIMT. Circulating form of SIGLEC-1 accelerates atherosclerosis and provides a simple way to predict the occurrence of atherosclerosis in SLE patients.