Publications

The muco-epithelial interface in the mammalian gut is composed of a mucus and epithelial lining fundamental to barrier function, microbe-host interactions, and intestinal homeostasis. This barrier is heavily glycosylated by O-linked sugars covalently linked to mucin glycoproteins, and N-linked sugars that coat epithelial surface proteins. Gut O- and N-glycans are thought to play central roles in barrier function, host defense, nutrition and attachment for commensals and pathogens, immunoregulation and cell-cell interactions. However, the precise nature of the glycans and how glycan composition changes through development, as a function of diet, and during inflammation, remains incompletely understood. Here, we apply O- and N-glycomic platforms to profile glycans on mucus and intestinal epithelium. By mapping individual glycan species spatially and temporally we identify 57 O- and 18 N-glycans in the mouse intestine, and observe that fucosylation and sialylation varies according to intestinal region and developmental stage. We identify a subset of glycans regulated by the gut microbiome, and observe a constriction of the glycan repertoire during inflammation in both mice and humans. Together, these results provide an atlas of individual intestinal glycans and their dynamic range through ontogeny and inflammation, and represent a significant resource for our understanding of the role of intestinal glycans in health and disease and glycan-focused therapies for intestinal inflammation and shaping the gut microbiome.

The H antigen (O blood group), the precursor to A and B blood groups, is expressed on human erythrocytes and other cells (e.g., endothelial cells). Remarkably, the specific expression of the H antigens is uncertain due to the lack of specific reagents for its detection. Here, we describe two monoclonal antibodies (mAbs), Tn4-31L and OmcFL3-02, generated by immunizing sea lampreys with human cells. Both mAbs are highly specific in comparison with the lectin Ulex europaeus agglutinin-I (UEA-I). We identified expression of H antigens in mammalian glycoproteins, human cells, and normal and malignant human tissues, discovering that different types of human carcinomas exhibit unexpected H antigen expression. Interestingly, H antigen detection in many cases was distinctly elevated by enzymatic desialylation, as well as being elevated in cells engineered to lack sialic acid. These highly specific mAbs will be valuable reagents in blood testing and for exploring the expression and function of H antigens.

Bacteria frequently employ carbohydrate-binding proteins, so-called lectins, to colonize and persist in a host. Thus, bacterial lectins are attractive targets for the development of new anti-infectives. To find new potential targets for anti-infectives against pathogenic bacteria, we searched for homologs of Pseudomonas aeruginosa lectins and identified homologs of LecA in Enterobacter species. Here, we recombinantly produced and biophysically characterized a homolog that comprises one LecA domain and one additional, novel protein domain. This protein was termed Enterobacter cloacae lectin A (EclA) and found to bind l-fucose. Glycan array analysis revealed a high specificity for the LewisA antigen and the type II H-antigen (blood group O) for EclA, while related antigens LewisX, Y, and B, as well as blood group A or B were not bound. We developed a competitive binding assay to quantify blood group antigen-binding specificity in solution. Finally, the crystal structure of EclA could be solved in complex with methyl α-l-selenofucoside. It revealed the unexpected binding of the carbohydrate ligand to the second domain, which comprises a novel fold that dimerizes via strand-swapping resulting in an intertwined beta sheet.

Pertussis toxin (PT) is a key protective antigen in vaccine- and natural immunity-mediated protection from Bordetella pertussis infection. Despite its importance, no PT-neutralizing epitopes have been characterized structurally. To define neutralizing epitopes and identify key structural elements to preserve during PT antigen design, we determined a 3.6 Å cryoelectron microscopy structure of genetically detoxified PT (PTg) bound to hu11E6 and hu1B7, two potently neutralizing anti-PT antibodies with complementary mechanisms: disruption of toxin adhesion to cells and intracellular activities, respectively. Hu11E6 binds the paralogous S2 and S3 subunits of PTg via a conserved epitope but surprisingly did not span the previously identified sialic acid-binding site implicated in toxin adhesion. Hu11E6 specifically prevented PTg binding to sialylated N-glycans and a sialylated model receptor, as demonstrated by high-throughput glycan array analysis and ELISA, while a T cell activation assay showed that it blocks PTg mitogenic activities to define its neutralizing mechanism. Hu1B7 bound a quaternary epitope spanning the S1 and S5 subunits, although functional studies of hu1B7 variants suggested that S5 binding is not involved in its PT neutralization mechanism. These results structurally define neutralizing epitopes on PT, improving our molecular understanding of immune protection from B. pertussis and providing key information for the future development of PT immunogens.

Bacteria often make initial contact with their hosts through the ligand-binding domains of large adhesin proteins. Recent analyses of repeats-in-toxin (RTX) adhesins in Gram-negative bacteria suggest that ligand-binding domains can be identified by the way they emerge from "split" domains within the adhesin. Here, using this criterion and an AlphaFold3 model of a 5047-residue RTX adhesin from Aeromonas hydrophila, we identified three different ligand-binding domains in this fibrillar protein. The crystal structures of the two novel domains were solved to 1.4 and 1.95 Å resolution, respectively, and demonstrate excellent agreement with their modeled structures. The other domain was recognized as a carbohydrate-binding module based on its beta-strand topology and confirmed by its micromolar affinity for fucosylated glycans, including the Lewis B and Y antigens. This lectin-like module, which was recombinantly produced with its companion split domain and nearby extender domain, bound to a wide variety of cells including yeasts, diatoms, erythrocytes, and human endothelial cells. In each case, 50 mM free fucose prevented this binding and may offer some protection from infection. The carbohydrate-binding module with its neighboring domains also caused aggregation of yeast and erythrocytes, which was again blocked by the addition of free fucose. The second putative ligand-binding domain has a beta-roll structure supported by a parallel alpha-helix, and the third is a homolog of a von Willebrand Factor A domain. These two domains bind to a more limited range of cell types, and their ligands have yet to be identified.IMPORTANCECharacterizing the ligand-binding domains of fibrillar adhesins is important for understanding how bacteria can colonize host surfaces and how this colonization might be blocked. Here, we show that the opportunistic pathogen, Aeromonas hydrophila, uses a carbohydrate-binding module (CBM) to attach to several different cell types. The CBM is one of three ligand-binding domains at the distal tip of the adhesin. Identifying the glycans bound by the CBM as Lewis B and Y antigens has helped explain the range of cell types that the bacterium will bind and colonize, and it has suggested sugars that might interfere with these processes. Indeed, fucose, which is a constituent of the Lewis B and Y antigens, is effective at 50 mM concentrations in blocking the attachment of the CBM to host cells. This will lead to the design of more effective inhibitors against bacterial infections.

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), a leading cause of death by an infectious disease globally, has no efficacious vaccine. Antibodies are implicated in M. tuberculosis control, but the mechanisms of action remain poorly understood. We assembled a library of monoclonal antibodies (mAb) and screened for M. tuberculosis-restrictive activity in mice, identifying protective antibodies targeting diverse antigens. To dissect the mechanism of mAb-mediated M. tuberculosis restriction, we optimized a protective lipoarabinomannan-specific mAb, generating Fc variants. In vivo analysis of these Fc variants revealed a role for Fc-effector function in M. tuberculosis restriction. Restrictive Fc variants altered distribution of M. tuberculosis across innate immune cells. Single-cell transcriptomics highlighted distinctly activated pathways within innate immune cell subpopulations, identifying early activation of neutrophils as a key signature of mAb-mediated M. tuberculosis restriction. Therefore, antibody-mediated restriction of M. tuberculosis is associated with reorganization of the tissue-level immune response to infection and depends on the collaboration of antibody Fab and Fc.

The endothelial glycocalyx, a glycan-rich layer on the luminal surface of endothelial cells lining blood and lymphatic vessels, plays a crucial role in vascular homeostasis by regulating vascular permeability, immune cell trafficking, and vascular tone. Dysregulated endothelial glycocalyx turnover-whether through altered synthesis, intracellular degradation, or shedding-contributes to endothelial dysfunction in conditions such as sepsis, ischemic events, and chronic inflammatory disorders including diabetes and atherosclerosis. In this review, we examine the structure, function, and turnover of the endothelial glycocalyx, emphasizing how pathological changes in its turnover drive vascular dysfunction. We also highlight diagnostic approaches to evaluate dysregulated endothelial glycocalyx turnover in connection with vascular diseases and discuss therapeutic strategies aimed at preventing endothelial glycocalyx degradation and restoring endothelial function.

The ability to rapidly analyze complex mixtures of glycans derived from glycoproteins is important, but techniques are often laborious and require multiple glycan derivatization steps. Here, we describe an approach termed Swift Universal Glycan Acquisition (SUGA) in which the total released, nonreduced N-glycan samples are analyzed following direct injection and electrospray ionization in a mass spectrometer with a rapid 3 min run time for each sample. As electrospray ionization (ESI) can generate multiple charge states and adducts for the same glycan composition (MS1), deconvolution is performed to yield the relative intensity profile for each detected glycan composition; each annotated composition is supported by an annotated MS2 spectrum. This combination of MS1 and MS2 data enables confident glycan identification. The data obtained by SUGA are comparable to those obtained using permethylated N-glycans analyzed by matrix-assisted laser desorption/ionization (MALDI)-MS. The SUGA approach was applied to the analyses of several purified glycoproteins and N-glycans derived from cells and compared to spectra obtained following permethylation and analysis by MALDI-MS. This new approach will facilitate the rapid and high-throughput analysis of N-glycans from diverse biological samples.

Specific recognition of glycans by proteins is important in many biological processes and immune responses. Here we present a general approach for derivatizing free glycans with a novel linker MTZ (3-(methoxyamino)-propylamine added to a bioorthogonal-functional tetrazine tag) that exploits click chemistry to generate multiple platforms of glycan coupling. This derivatization preserves glycan integrity, is reversible and quantifiable, and incorporates a bioorthogonal tetrazine tag for click coupling. A library of ABO-(H) blood group MTZ-glycans was efficiently conjugated to avidin Luminex beads through a Biotin-PEG11-TCO (trans-cyclooctene) spacer, generating a multiplex array that was reproducibly interrogated in a high-throughput Luminex approach with multiple lectins and antibodies. We also rapidly profiled antiglycan IgG, IgM, and IgA antibodies in multiple, serially diluted human serum samples, revealing unique repertoires of antiglycan responses in each sera. Glycans were efficiently coupled to bovine serum albumin (BSA) at a high density (∼19-24 glycans/BSA) to generate a neoglycoprotein library that was useful in microarray formats that provided results equivalent to those obtained from the Luminex approach. Neoglycoproteins have many uses, including serving as acceptors for glycosyltransferases, as we demonstrate for assays of ST6Gal1 sialyltransferase. These facile and efficient technologies significantly expand the toolbox available to explore glycan-GBP interactions.

Protein O-glycosylation is a critical modification in the brain, as genetic variants in the pathway are associated with common and severe neuropsychiatric phenotypes. However, little is known about the most abundant O-glycans in the mammalian brain, which are N-acetylgalactosamine (O-GalNAc) linked. Here, we determined the spatial localization, protein carriers, and cellular function of O-GalNAc glycans in the mouse brain. We observed striking spatial enrichment of O-GalNAc glycans in neuronal tracts, and specifically at nodes of Ranvier, specialized structures involved in signal propagation in the brain. Glycoproteomic analysis revealed that more than half of the identified O-GalNAc glycans were present on chondroitin sulfate proteoglycans termed lecticans, and display both domain enrichment and regional heterogeneity. Inhibition of O-GalNAc synthesis in neurons reduced binding of Siglec-4, a known regulator of neurite growth, and shortened the length of nodes of Ranvier. This work establishes a function of O-GalNAc glycans in the brain and will inform future studies on their role in development and disease.