Synthetic glyco-O-sulfatome for profiling of human natural antibodies

Caution, these are glycan sulfates. The features of their interaction with proteins

In studies of viruses, lectins and especially human blood anti-glycan antibodies using printed glycan array (PGA), sulfated glycans suspiciously often turn out to be the highest-level binders. The binding to sulfated glycan along with parent neutral is easily explained by the similarity of these two glycans, while the unexpected thing is the many times stronger binding. Analysis of data accumulated over almost two decades allows us to explain the observed effect by the Coulomb interaction of the sulfate residue with a positively charged amino acid that accidently appears near the binding site of the neutral glycan backbone. That is, there is an effect of enhancing the specific interaction by an additional electrostatic one. It is expected that the material considered in the article will be useful for the correct interpretation of other data on the specificity of proteins capable of binding charged glycans, which are often encountered in nature.

Enzyme-Sialylation-Controlled Chemical Sulfation of Glycan Epitopes for Decoding the Binding of Siglec Ligands

Widely distributed in nature, sulfated glycan epitopes play important roles in diverse pathophysiological processes. However, due to their structural complexity, the preparation of glycan epitopes with structurally defined sulfation patterns is challenging, which significantly hampers the detailed elucidation of their biological functions at the molecular level. Here, we introduce a strategy for site-specific chemical sulfation of glycan epitopes, leveraging enzymatic sialylation and desialylation processes to precisely control the regio-specificity of sulfation of disaccharide or trisaccharide glycan backbones. Using this method, a sulfated glycan library covering the most common sialylated glycan epitopes was prepared in high yield and efficiency. By screening a microarray prepared with this glycan library, we systematically probed their binding specificity with human Siglecs (sialic acid-binding immunoglobulin-type lectins), many of which function as glyco-immune checkpoints to suppress immune system activation. Our investigation revealed that sulfation and sialylation patterns serve as important determinants of Siglec binding affinity and specificity. Thus, these findings offer new insights for the development of research tools and potential therapeutic agents targeting glyco-immune checkpoints by modulating the Siglec signaling pathway.

Serum antibody screening using glycan arrays

Humans and other animals produce a diverse collection of antibodies, many of which bind to carbohydrate chains, referred to as glycans. These anti-glycan antibodies are a critical part of our immune systems' defenses. Whether induced by vaccination or natural exposure to a pathogen, anti-glycan antibodies can provide protection against infections and cancers. Alternatively, when an immune response goes awry, antibodies that recognize self-glycans can mediate autoimmune diseases. In any case, serum anti-glycan antibodies provide a rich source of information about a patient's overall health, vaccination history, and disease status. Glycan microarrays provide a high-throughput platform to rapidly interrogate serum anti-glycan antibodies and identify new biomarkers for a variety of conditions. In addition, glycan microarrays enable detailed analysis of the immune system's response to vaccines and other treatments. Herein we review applications of glycan microarray technology for serum anti-glycan antibody profiling.

Specificity of viscumin revised. As probed with a printed glycan array

Viscumin, a lectin used in anti-cancer therapy, was originally considered as βGal recognizing protein; later, an ability to bind 6'-sialyl N-acetyllactosamine (6'SLN) terminated gangliosides was found. Here we probed viscumin with a printed glycan array (PGA) containing a large number of mammalian sulfated glycans, and found a strong binding to glycans with 6-O-SuGal moiety as lactose, N-acetyllactosamine (LN), di-N-acetyllactosamine (LacdiNAc), and even 6-O-SuGalNAcα (but not SiaTn). Also, the ability to bind some of αGal terminated glycans, including Galα1-3Galβ1-4GlcNAc, was observed. Unexpectedly, only weak interaction was detected with parent neutral β-galactosides including LN-LN-LN and branched (LN)₂LN oligolactosamines; in the light of these data, one should not confidently classify viscumin as a β-galactoside-binding lectin. Carrying out PGA in the presence of neutral or sulfated/sialylated glycan, together with sequential elution from lactose-sepharose and consideration of the protein structure, lead to the conclusion that two glycan-binding sites of viscumin have different specificities, one of which prefers charged sulfated and sialylated moieties.

Trifluoroacetic acid-promoted ring contraction in 2,3-di-O-silylated O-galactopyranosides and hemiacetals

A pyranose ring contraction of 2,3-di-O-silylated O-galactopyranosides with retention of aglycone promoted by anhydrous trifluoroacetyc acid (TFA) in CH2Cl2 was demonstrated for the first time. In addition, TFA-promoted pyranose ring contraction of 2,3-bis-O-(triisopropylsilyl)-D-galactopyranose with formation of the corresponding anomeric triols in furanose form was successfully performed. A representative series of β-D-galactopyranosides with Me, Bn, allyl, or 3-(trifluoroacetamido)propyl aglycones has been investigated. TBDPS protective groups were found to be more stable than TIPS groups under conditions of TFA-promoted pyranose ring contraction. An easy access to 2,3-di-O-TBDPS substituted allyl and benzyl galactofuranosides and 2,3-bis-O-(triisopropylsilyl)-β-D-galactofuranose may present an advantage in synthesis of selectively protected monosacharide bilding blocks, useful for the synthesis of biologically important oligosaccharides.

Anti-glycan antibodies: roles in human disease

Carbohydrate-binding antibodies play diverse and critical roles in human health. Endogenous carbohydrate-binding antibodies that recognize bacterial, fungal, and other microbial carbohydrates prevent systemic infections and help maintain microbiome homeostasis. Anti-glycan antibodies can have both beneficial and detrimental effects. For example, alloantibodies to ABO blood group carbohydrates can help reduce the spread of some infectious diseases, but they also impose limitations for blood transfusions. Antibodies that recognize self-glycans can contribute to autoimmune diseases, such as Guillain-Barre syndrome. In addition to endogenous antibodies that arise through natural processes, a variety of vaccines induce anti-glycan antibodies as a primary mechanism of protection. Some examples of approved carbohydrate-based vaccines that have had a major impact on human health are against pneumococcus, Haemophilus influeanza type b, and Neisseria meningitidis. Monoclonal antibodies specifically targeting pathogen associated or tumor associated carbohydrate antigens (TACAs) are used clinically for both diagnostic and therapeutic purposes. This review aims to highlight some of the well-studied and critically important applications of anti-carbohydrate antibodies.