Publications

BACKGROUND: Immunoglobulin G (IgG) plays a critical role in immune defense yet our understanding of its role in cardiovascular disease (CVD) is evolving. Observational studies have correlated statin use with changes in IgG N-glycan structures. However, statin effects on IgG N-glycan changes have not been tested in randomized controlled trials, and their direct association with CVD remains unclear.

METHODS: IgG N-glycans were measured at baseline and after one year of randomized high-intensity statin interventions in 2 sub-studies of randomized trials: JUPITER (Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin; NCT00239681; primary prevention; discovery, n = 239 participants); and TNT (Treating to New Targets; NCT00327691; secondary prevention; validation, n = 711). Using linear regression adjusted for baseline levels of IgG N-glycans and clinical risk factors (e.g., age, sex) as well as the occurrence of CVD during the year of follow-up, we investigated the one-year randomized effects of high-intensity rosuvastatin v. placebo on IgG N-glycans in JUPITER. Significant statin-IgG N-glycan associations were then validated in TNT with one-year randomized effects of high- v. low-intensity atorvastatin intervention. We examined the architecture of IgG N-glycan connectivity at baseline using a data-driven Bayesian network and compared it with the architecture after one year of randomized statin intervention. We then investigated whether the changes in IgG N-glycans triggered by statins were associated with incident CVD events.

RESULTS: We identified 5 IgG N-glycans (corresponding to core fucosylated, monosialylated, and disialylated IgG N-glycans) in JUPITER whose levels decreased significantly with statin versus placebo (false discovery rate < 0.05), with an approximate 11.3-25.9% reduction in the individual IgG N-glycan levels. Four out of the five IgG N-glycans altered by statin were validated in TNT. Furthermore, monosialylation and core fucosylation (glycan peaks, GP 16 and 18) were inversely associated with CVD in JUPITER (OR = 0.87 and 0.73 per standard deviation increase, 95% CI: (0.57, 0.98) and (0.55, 0.96) respectively), and validated in TNT. Despite the effect of statin therapy on certain IgG N-glycans, the overall architecture of the IgG N-glycan network remained unchanged after one year of statin intervention.

CONCLUSION: High-intensity statin interventions decreased several specific IgG N-glycan levels without changing the overall architecture of IgG N-glycan connectivity. Two IgG N-glycans that were decreased by statins were inversely associated with CVD outcomes, suggesting that statins have effects on monosialylated and core fucosylated IgG N-glycans, which may affect their cardioprotective properties. These findings highlight a potential immunomodulatory role of statins through IgG N-glycan alterations that should be further investigated in relation to CVD.

Cosmc, encoded by the X-linked C1GALT1C1, is a molecular chaperone in the endoplasmic reticulum and a master regulator of O-glycosylation of mammalian glycoproteins. Recently, we described a germline mutation in C1GALT1C1 in two male patients, giving rise to a congenital disorder of glycosylation-COSMC-CDG. Here, we have identified a female patient with a de novo mosaic variant in C1GALT1C1 (c.202C>T, p.Arg68*), which results in a truncated and nonfunctional form of Cosmc (Cosmc-R68). The patient is mosaic, as  27% of her buccal cells carry the mutation. The patient is now a 5-year old who presented with nonimmune hydrops fetalis. As Cosmc is essential for the generation of normal O-glycans through regulating T-synthase activity, thereby enabling the formation of the universal Core 1 O-glycan Galβ1-3GalNAcα1-Ser/Thr (T-antigen), the loss of Cosmc leads to the expression of the unusual precursor O-glycan termed Tn-antigen (CD175) (GalNAcα1-Ser/Thr). Owing to the mutational mosaicism, only a significant minority of cells would exhibit abnormal O-glycosylation. Analysis of red blood cells (RBCs), leukocytes, and serum from this patient indicated reduced expression of Cosmc and T-synthase proteins and lower T-synthase activity. Consistent with these findings, we observed reduced normal O-glycans in serum glycoproteins and RBCs from the patient, along with elevated expression of the Tn-antigen in serum glycoproteins compared to controls. This case represents the first description of a true mosaic loss-of-function variant in C1GALT1C1, that is, one that occurred postzygotically during embryogenesis, and raises interesting questions about the role of O-glycosylation during fetal development and its consequences on the clinical presentation.

Alterations in protein glycosylation are observed in many solid tumor types leading to formation of tumor-associated carbohydrate antigens (TACAs). The most common TACA is the Tn antigen (CD175), which is a mucin-type O-GalNAc-Ser/Thr/Tyr glycan in membrane and secreted glycoproteins. In addition, two other TACAs are CA19-9 (sialyl-Lewis a), which is used as a prognostic serum marker for pancreatic cancer, and its isomer sialyl-Lewis x (SLex, CD15s), which is overexpressed in many cancer types and associated with metastasis. While CD175 and other TACAs may be expressed by many human carcinomas, little is known about their differential expression patterns in tumors, thus limiting their use as tissue biomarkers or therapeutic targets. Here we address the clinicopathological relevance of the expression of CA19-9, CD15s, and CD175 in pancreatic ductal adenocarcinoma (PDAC) tissues. Semi-quantitative IHC staining with well-defined monoclonal antibodies demonstrates that CD175 is expressed in all PDAC specimens analyzed. Unexpectedly, however, these TACAs are differentially expressed within PDAC specimens and their glycoproteins, but not significantly expressed in adjacent normal tissues. These data provide avenues for novel therapeutic approaches that could combine CD175- and CA19-9-targeting therapies for PDAC patients.

Sickle Cell Disease (SCD) is a severe genetic disorder causing vascular occlusion and pain by upregulating the adhesion molecule P-selectin on endothelial cells and platelets. It primarily affects infants and children, causing chronic pain, circulatory problems, organ damage, and complications. Thus, effective treatment and management are crucial to reduce SCD-related risks. Anti-P-selectin antibody Crizanlizumab (Crimab) has been used to treat SCD. In this study, the heavy and light chain (HC and LC) genes of anti-P-Selectin antibody Crimab were cloned into a plant expression binary vector. The HC gene was under control of the duplicated 35S promoter and nopaline synthase (NOS) terminator, whereas the LC gene was under control of the potato proteinase inhibitor II (PIN2) promoter and PIN2 terminator. Agrobacterium tumefaciens LBA4404 was used to transfer the genes into the tobacco (Nicotiana tabacum cv. Xanthi) plant. In plants the genomic PCR and western blot confirmed gene presence and expression of HC and LC Crimab proteins in the plant, respectively. Crimab was successfully purified from transgenic plant leaf using protein A affinity chromatography. In ELISA, plant-derived Crimab (CrimabP) had similar binding activity to P-selectin compared to mammalian-derived Crimab (CrimabM). In surface plasmon resonance, the KD (dissociation binding constant) and response unit values were lower and higher than CrimabP, respectively. Taken together, these results demonstrate that the transgenic plant can be applied to produce biofunctional therapeutic monoclonal antibody.

The anaerobic spirochete Brachyspira causes intestinal spirochetosis, characterized by the intimate attachment of bacterial cells to the colonic mucosa, potentially leading to symptoms such as diarrhea, abdominal pain, and weight loss. Despite the clinical significance of Brachyspira infections, the mechanism of the interaction between Brachyspira and the colon epithelium is not known. We characterized the molecular mechanism of the B. pilosicoli-epithelium interaction and its impact on the epithelial barrier during infection. Through a proteomics approach, we identified BPP43_05035 as a candidate B. pilosicoli surface protein that mediates bacterial attachment to cultured human colonic epithelial cells. The crystal structure of BPP43_05035 revealed a globular lipoprotein with a six-bladed beta-propeller domain. Blocking the native BPP43_05035 on B. pilosicoli, either with a specific antibody or via competitive inhibition, abrogated its binding to epithelial cells, which required cell surface-exposed N-glycans. Proximity labeling and interaction assays revealed that BPP43_05035 bound to tight junctions, thereby increasing the permeability of the epithelial monolayer. Extending our investigation to humans, we discovered a downregulation of tight junction and brush border genes in B. pilosicoli-infected patients carrying detectable levels of epithelium-bound BPP43_05035. Collectively, our findings identify BPP43_05035 as a B. pilosicoli adhesin that weakens the colonic epithelial barrier during infection.

Many pathogenic Gram-negative bacteria use repeats-in-toxin adhesins for colonization and biofilm formation. In the cholera agent Vibrio cholerae, flagellar-regulated hemagglutinin A (FrhA) enables these functions. Using bioinformatic analysis, a sugar-binding domain was identified in FrhA adjacent to a domain of unknown function. AlphaFold2 indicated the boundaries of both domains to be slightly shorter than previously predicted and assisted in the recognition of the unknown domain as a split immunoglobulin-like fold that can assist in projecting the sugar-binding domain toward its target. The AlphaFold2-predicted structure is in excellent agreement with the molecular envelope obtained from small-angle X-ray scattering analysis of a recombinant construct spanning the sugar-binding and unknown domains. This two-domain construct was probed by glycan micro-array screening and showed binding to mammalian fucosylated glycans, some of which are characteristic erythrocyte markers and intestinal cell epitopes. Isothermal titration calorimetry further showed the construct-bound l-fucose with a Kd of 21 µM. Strikingly, this recombinant protein construct bound and lysed erythrocytes in a concentration-dependent manner, and its hemolytic activity was blocked by the addition of l-fucose. A protein ortholog construct from Aeromonas veronii was also produced and showed a similar glycan-binding pattern, binding affinity, erythrocyte-binding, and hemolytic activities. As demonstrated here with Hep-2 cells, fucose-based inhibitors of this sugar-binding domain can potentially be developed to block colonization by V. cholerae and other pathogenic bacteria that share this adhesin domain.IMPORTANCEThe bacterium, Vibrio cholerae, which causes cholera, uses an adhesion protein to stick to human cells and begin the infection process. One part of this adhesin protein binds to a particular sugar, fucose, on the surface of the target cells. This binding can lead to colonization and killing of the cells by the bacteria. Adding l-fucose to the bacteria before they bind to the human cells can prevent attachment and has promise as a preventative drug to protect against cholera.

The relationship between protein stability and functional evolution is little explored in proteins purified from natural sources. Here, we investigated a novel family of egg proteins (Perivitellin-1, PV1) from Pomacea snails. Their remarkable stability and clade-related functions in most derived clades (Canaliculata and Bridgesii) make them excellent candidates for exploring this issue. To that aim, we studied PV1 (PpaPV1) from the most basal lineage, Flagellata. PpaPV1 displays unparalleled structural and kinetic stability, surpassing PV1s from derived clades, ranking among the most hyperstable proteins documented in nature. Its spectral features contribute to a pale egg coloration, exhibiting a milder glycan binding lectin activity with a narrower specificity than PV1s from the closely related Bridgesii clade. These findings provide evidence for substantial structural and functional changes throughout the genus' PV1 evolution. We observed that structural and kinetic stability decreased in a clade-related fashion and was associated with large variations in defensive traits. For instance, pale PpaPV1 lectin turns potent in the Bridgesii clade, adversely affecting gut morphology, while giving rise to brightly colored PV1s providing eggs with a conspicuous, probably warning signal in the Canaliculata clade. This work provides a comprehensive comparative analysis of PV1s from various apple snail species within a phylogenetic framework, offering insights into the interplay among their structural features, stability profiles and functional roles. More broadly, our work provides one of the first examples from natural evolution showing the crucial link among protein structure, stability and evolution of new functions.

Glycans linked to proteins and lipids and also occurring in free forms have many functions, and these are partly elicited through specific interactions with glycan-binding proteins (GBPs). These include lectins, adhesins, toxins, hemagglutinins, growth factors, and enzymes, but antibodies can also bind glycans. While humans and other animals generate a vast repertoire of GBPs and different glycans in their glycomes, other organisms, including phage, microbes, protozoans, fungi, and plants also express glycans and GBPs, and these can also interact with their host glycans. This can be termed the protein-glycan interactome, and in nature is likely to be vast, but is so far very poorly described. Understanding the breadth of the protein-glycan interactome is also a key to unlocking our understanding of infectious diseases involving glycans, and immunology associated with antibodies binding to glycans. A key technological advance in this area has been the development of glycan microarrays. This is a display technology in which minute quantities of glycans are attached to the surfaces of slides or beads. This allows the arrayed glycans to be interrogated by GBPs and antibodies in a relatively high throughput approach, in which a protein may bind to one or more distinct glycans. Such binding can lead to novel insights and hypotheses regarding both the function of the GBP, the specificity of an antibody and the function of the glycan within the context of the protein-glycan interactome. This article focuses on the types of glycan microarray technologies currently available to study animal glycobiology and examples of breakthroughs aided by these technologies.

The synapse is an essential connection between neuronal cells in which the membrane and secreted glycoproteins regulate neurotransmission. The post-translational modifications of glycoproteins with carbohydrates, although essential for their functions as well as their specific localization, are not well understood. Oddly, whereas galactose addition to glycoproteins is required for neuronal functions, galactosylation is severely restricted for Asn-linked on N-glycans in the brain, and genetic evidence highlights the important roles of galactose in brain functions and development. To explore this novel glycosylation, we exploited an orthogonal technology in which a biotinylated sialic acid derivative (CMP-biotin-Sia) is transferred to terminally galactosylated proteins by a recombinant sialyltransferase (rST6Gal1). This approach allowed us to identify the carrier proteins as well as their localization on brain sections. Immunohistochemical analysis of the biotinylated glycoproteins in brain sections demonstrates that they are largely positioned in the pre- and postsynaptic membranes. Consistent with this positioning, glycoproteomic analyses of the labeled glycoproteins identified a number of them that are involved in synaptic function, cell adhesion, and extracellular matrix interactions. The discovery of these galactosylated N-glycoproteins and their relative confinement to synapses provide novel insights into the unusual and specific nature of protein glycosylation in the brain.

Aberrant protein glycosylation is a hallmark alteration of cancer and is highly associated with cancer progression. Papillary thyroid cancer (PTC) is the most common type of thyroid cancer, but the N-glycosylation of its glycoproteins has not been well characterized. In this work, we analyzed multiple freshly prepared PTC specimens along with paired normal tissue obtained from thyroidectomies. Glycomic analyses focused on Asn-linked (N)-glycans and employed mass spectrometry (MS), along with Western blot approaches of total solubilized materials that were examined for binding by specific lectins and a monoclonal antibody (mAb) O6, specific for 3-O-sulfated galactose residues. We observed major differences in PTC versus paired normal specimens, as PTC specimens exhibited higher levels of N-glycan branching and bisection with N-acetylglucosamine residues, consistent with RNAseq data. We also found that 3-O-sulfated galactose was present in N-glycans of multiple glycoproteins from both PTC and control specimens, as recognized by the O6 mAb and as confirmed by MS analyses. These results provide new insights into the N-glycans present in glycoproteins of thyroid cancer and context for further studies of these altered glycans as biomarkers and targets for therapeutics.