Non-carbohydrate-mediated interaction of lectins with plant proteins

Metabolic reprogramming and membrane glycan remodeling as potential drivers of zebrafish heart regeneration

The ability of the zebrafish heart to regenerate following injury makes it a valuable model to deduce why this capability in mammals is limited to early neonatal stages. Although metabolic reprogramming and glycosylation remodeling have emerged as key aspects in many biological processes, how they may trigger a cardiac regenerative response in zebrafish is still a crucial question. Here, by using an up-to-date panel of transcriptomic, proteomic and glycomic approaches, we identify a metabolic switch from mitochondrial oxidative phosphorylation to glycolysis associated with membrane glycosylation remodeling during heart regeneration. Importantly, we establish the N- and O-linked glycan structural repertoire of the regenerating zebrafish heart, and link alterations in both sialylation and high mannose structures across the phases of regeneration. Our results show that metabolic reprogramming and glycan structural remodeling are potential drivers of tissue regeneration after cardiac injury, providing the biological rationale to develop novel therapeutics to elicit heart regeneration in mammals.

Calculating Half Maximal Inhibitory Concentration (IC50) Values from Glycomics Microarray Data Using GraphPad Prism

Half maximal inhibitory concentration (IC₅₀) is a measurement often used to compare the efficiency of various carbohydrates and their derivatives for inhibition of lectin binding to particular ligands. IC₅₀ values can be calculated using experimental data from various platforms including enzyme-linked immunosorbent assay- (ELISA-)type microtiter plate assays, isothermal titration calorimetry (ITC), or glycan microarrays. In this chapter, we describe methods to fluorescently label a lectin, to carry out a lectin binding inhibition experiment on glycan microarrays, and to calculate the IC₅₀ value of a binding inhibitory molecule using GraphPad Prism software. In the example used to illustrate the method in this chapter, IC₅₀ calculation is demonstrated for inhibition of Maackia amurensis agglutinin (MAA) binding to 3'sialyl-N-acetyllactosamine (3SLN) using free lactose.

Lectin Histochemistry for Tissues and Cells, and Dual Lectin and Antibody Co-localization

In this chapter we describe in detail methods for lectin staining of (1) tissues, and (2) cells to identify and map endogenous glycosylation. We also describe (3) dual antibody and lectin staining of tissues to associate glycosylation with particular proteins or cells in tissues.

An optimized protocol for combined fluorescent lectin/immunohistochemistry to characterize tissue-specific glycan distribution in human or rodent tissues

Lectin histochemical analysis of tissues combined with immunohistochemistry is a valuable tool to characterize and correlate the spatial distribution of glycans with the presence of specific cell types or antigens of interest. The current protocol describes the application of monosaccharide motif specificity of lectin binding to glycan residues to different tissue types. In addition, we describe stereological methods to provide further quantification of the analyzed tissues.

For complete details on the use and execution of this protocol, please refer to Mohd Isa et al. (2018), Contessotto et al. (2020), and Samal et al. (2020).

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Periodate-pretreated bovine serum albumin as a blocking reagent for lectin staining/IHC

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Combined lectin histochemistry and immunohistochemistry staining procedure

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Co-localization of glycan distribution with expression of antigens of interest

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Quantification of fluorescence intensity and positively stained area fraction

Distinct glycosylation in membrane proteins within neonatal versus adult myocardial tissue

Mammalian hearts have regenerative potential restricted to early neonatal stage and lost within seven days after birth. Carbohydrates exclusive to cardiac neonatal tissue may be key regulators of regenerative potential. Although cell surface and extracellular matrix glycosylation are known modulators of tissue and cellular function and development, variation in cardiac glycosylation from neonatal tissue to maturation has not been fully examined. In this study, glycosylation of the adult rat cardiac ventricle showed no variability between the two strains analysed, nor were there any differences between the glycosylation of the right or left ventricle using lectin histochemistry and microarray profiling. However, in the Sprague-Dawley strain, neonatal cardiac glycosylation in the left ventricle differed from adult tissues using mass spectrometric analysis, showing a higher expression of high mannose structures and lower expression of complex N-linked glycans in the three-day-old neonatal tissue. Man₆GlcNAc₂ was identified as the main high mannose N-linked structure that was decreased in adult while higher expression of sialylated N-linked glycans and lower core fucosylation for complex structures were associated with ageing. The occurrence of mucin core type 2 O-linked glycans was reduced in adult and one sulfated core type 2 O-linked structure was identified in neonatal tissue. Interestingly, O-linked glycans from mature tissue contained both N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), while all sialylated N-linked glycans detected contained only Neu5Ac. As glycans are associated with intracellular communication, the specific neonatal structures found may indicate a role for glycosylation in the neonatal associated regenerative capacity of the mammalian heart. New strategies targeting tissue glycosylation could be a key contributor to achieve an effective regeneration of the mammalian heart in pathological scenarios such as myocardial infarction.

Differential Glycosylation Expression in Injured Rat Spinal Cord Treated with Immunosuppressive Drug Cyclosporin-A

Glycosylation is ubiquitous throughout the central nervous system and altered following spinal cord injury (SCI). The glial scar that forms following SCI is composed of several chondroitin sulfate proteoglycans, which inhibit axonal regrowth. Cyclosporin-A (CsA), an immunosuppressive therapeutic, has been proposed as a potential treatment after SCI. We investigated CsA treatment in the spinal cord of healthy, contusion injured, and injured CsA-treated rats. Lectin histochemistry using fluorescently labeled lectins, SBA, MAA, SNA-I, and WFA, was performed to identify the terminal carbohydrate residues of glycoconjugates within the spinal cord. SBA staining decreased in gray and white matter following spinal cord injury, whereas staining was increased at the lesion site in CsA-treated animals, indicating an increase in galactose and N-acetylgalactosamine terminal structures. No significant changes in MAA were observed. WFA staining was abundant in gray matter and observed to increase at the lesion site, in agreement with increased expression of chondroitin sulfate proteoglycans. SNA-I-stained blood vessels in all spinal cord regions and dual staining identified a subpopulation of astrocytes in the lesion site, which expressed α-(2,6)-sialic acid. Glycosylation were altered in injured spinal cord treated with CsA, indicating that glycosylation and alteration of particular carbohydrate structures are important factors to consider in the examination of the environment of the spinal cord after injury.

Structure and N-acetylglucosamine binding of the distal domain of mouse adenovirus 2 fibre

Murine adenovirus 2 (MAdV-2) infects cells of the mouse gastrointestinal tract. Like human adenoviruses, it is a member of the genus Mastadenovirus, family Adenoviridae. The MAdV-2 genome has a single fibre gene that expresses a 787 residue-long protein. Through analogy to other adenovirus fibre proteins, it is expected that the carboxy-terminal virus-distal head domain of the fibre is responsible for binding to the host cell, although the natural receptor is unknown. The putative head domain has little sequence identity to adenovirus fibres of known structure. In this report, we present high-resolution crystal structures of the carboxy-terminal part of the MAdV-2 fibre. The structures reveal a domain with the typical adenovirus fibre head topology and a domain containing two triple β-spiral repeats of the shaft domain. Through glycan microarray profiling, saturation transfer difference nuclear magnetic resonance spectroscopy, isothermal titration calorimetry and site-directed mutagenesis, we show that the fibre specifically binds to the monosaccharide N-acetylglucosamine (GlcNAc). The crystal structure of the complex reveals that GlcNAc binds between the AB and CD loops at the top of each of the three monomers of the MAdV-2 fibre head. However, infection competition assays show that soluble GlcNAc monosaccharide and natural GlcNAc-containing polymers do not inhibit infection by MAdV-2. Furthermore, site-directed mutation of the GlcNAc-binding residues does not prevent the inhibition of infection by soluble fibre protein. On the other hand, we show that the MAdV-2 fibre protein binds GlcNAc-containing mucin glycans, which suggests that the MAdV-2 fibre protein may play a role in viral mucin penetration in the mouse gut.

Rapid screening for specific glycosylation and pathogen interactions on a 78 species avian egg white glycoprotein microarray

There is an urgent need for discovery of novel antimicrobials and carbohydrate-based anti-adhesive strategies are desirable as they may not promote resistance. Discovery of novel anti-adhesive molecules from natural product libraries will require the use of a high throughput screening platform. Avian egg white (EW) provides nutrition for the embryo and protects against infection, with glycosylation responsible for binding certain pathogens. In this study, a microarray platform of 78 species of avian EWs was developed and profiled for glycosylation using a lectin panel with a wide range of carbohydrate specificities. The dominating linkages of sialic acid in EWs were determined for the first time using the lectins MAA and SNA-I. EW glycosylation similarity among the different orders of birds did not strictly depend on phylogenetic relationship. The interactions of five strains of bacterial pathogens, including Escherichia coli, Staphylococcus aureus and Vibrio cholera, identified a number of EWs as potential anti-adhesives, with some as strain- or species-specific. Of the two bacterial toxins examined, shiga-like toxin 1 subunit B bound to ten EWs with similar glycosylation more intensely than pigeon EW. This study provides a unique platform for high throughput screening of natural products for specific glycosylation and pathogen interactions. This platform may provide a useful platform in the future for discovery of anti-adhesives targeted for strain and species specificity.

Fasciola hepatica Surface Tegument: Glycoproteins at the Interface of Parasite and Host

Fasciola hepatica, commonly known as liver fluke, is a trematode that causes Fasciolosis in ruminants and humans. The outer tegumental coat of F. hepatica (FhTeg) is a complex metabolically active biological matrix that is continually exposed to the host immune system and therefore makes a good vaccine target. F. hepatica tegumental coat is highly glycosylated and helminth-derived immunogenic oligosaccharide motifs and glycoproteins are currently being investigated as novel vaccine candidates. This report presents the first systematic characterization of FhTeg glycosylation using lectin microarrays to characterize carbohydrates motifs present, and lectin histochemistry to localize these on the F. hepatica tegument. We discovered that FhTeg glycoproteins are predominantly oligomannose oligosaccharides that are expressed on the spines, suckers and tegumental coat of F. hepatica and lectin blot analysis confirmed the abundance of N- glycosylated proteins. Although some oligosaccharides are widely distributed on the fluke surface other subsets are restricted to distinct anatomical regions. We selectively enriched for FhTeg mannosylated glycoprotein subsets using lectin affinity chromatography and identified 369 proteins by mass spectrometric analysis. Among these proteins are a number of potential vaccine candidates with known immune modulatory properties including proteases, protease inhibitors, paramyosin, Venom Allergen-like II, Enolase and two proteins, nardilysin and TRIL, that have not been previously associated with F. hepatica. Furthermore, we provide a comprehensive insight regarding the putative glycosylation of FhTeg components that could highlight the importance of further studies examining glycoconjugates in host-parasite interactions in the context of F. hepatica infection and the development of an effective vaccine.

Unique glycosignature for intervertebral disc and articular cartilage cells and tissues in immaturity and maturity

In this study, on/off markers for intervertebral disc (IVD) and articular cartilage (AC) cells (chondrocytes) and distinct glycoprofiles of cell and tissue-types were identified from immaturity to maturity. Three and eleven month-old ovine IVD and AC tissues were histochemically profiled with a panel of lectins and antibodies. Relationships between tissue and cell types were analysed by hierarchical clustering. Chondroitin sulfate (CS) composition of annulus fibrosus (AF), nucleus pulposus (NP) and AC tissues was determined by HPLC analysis. Clear on/off cell type markers were identified, which enabled the discrimination of chondrocytes, AF and NP cells. AF and NP cells were distinguishable using MAA, SNA-I, SBA and WFA lectins, which bound to both NP cells and chondrocytes but not AF cells. Chondrocytes were distinguished from NP and AF cells with a specific binding of LTA and PNA lectins to chondrocytes. Each tissue showed a unique CS composition with a distinct switch in sulfation pattern in AF and NP tissues upon disc maturity while cartilage maintained the same sulfation pattern over time. In conclusion, distinct glycoprofiles for cell and tissue-types across age groups were identified in addition to altered CS composition and sulfation patterns for tissue types upon maturity.

Structure and Sialyllactose Binding of the Carboxy-Terminal Head Domain of the Fibre from a Siadenovirus, Turkey Adenovirus 3

The virulent form of turkey adenovirus 3 (TAdV-3), also known as turkey hemorrhagic enteritis virus (THEV), is an economically important poultry pathogen, while the avirulent form is used as a vaccine. TAdV-3 belongs to the genus Siadenovirus. The carboxy-terminal region of its fibre does not have significant sequence similarity to any other adenovirus fibre heads of known structure. Two amino acid sequence differences between virulent and avirulent TAdV-3 map on the fibre head: where virulent TAdV-3 contains Ile354 and Thr376, avirulent TAdV-3 contains Met354 and Met376. We determined the crystal structures of the trimeric virulent and avirulent TAdV-3 fibre head domains at 2.2 Å resolution. Each monomer contains a beta-sandwich, which, surprisingly, resembles reovirus fibre head more than other adenovirus fibres, although the ABCJ-GHID topology is conserved in all. A beta-hairpin insertion in the C-strand of each trimer subunit embraces its neighbouring monomer. The avirulent and virulent TAdV-3 fibre heads are identical apart from the exact orientation of the beta-hairpin insertion. In vitro, sialyllactose was identified as a ligand by glycan microarray analysis, nuclear magnetic resonance spectroscopy, and crystallography. Its dissociation constant was measured to be in the mM range by isothermal titration calorimetry. The ligand binds to the side of the fibre head, involving amino acids Glu392, Thr419, Val420, Lys421, Asn422, and Gly423 binding to the sialic acid group. It binds slightly more strongly to the avirulent form. We propose that, in vivo, the TAdV-3 fibre may bind a sialic acid-containing cell surface component.

Extracellular vesicles from Paracoccidioides pathogenic species transport polysaccharide and expose ligands for DC-SIGN receptors

Extracellular vesicles (EVs) mediate non-conventional transport of molecules across the fungal cell wall. We aimed at describing the carbohydrate composition and surface carbohydrate epitopes of EVs isolated from the pathogenic fungi Paracoccidioides brasiliensis and P. lutzii using standard procedures. Total EV carbohydrates were ethanol-precipitated from preparations depleted of lipids and proteins, then analyzed by chemical degradation, gas chromatography-mass spectrometry, nuclear magnetic resonance and size-exclusion chromatography. EV glycosyl residues of Glc, Man, and Gal comprised most probably two major components: a high molecular mass 4,6-α-glucan and a galactofuranosylmannan, possibly an oligomer, bearing a 2-α-Manp main chain linked to β-Galf (1,3) and α-Manp (1,6) end units. The results also suggested the presence of small amounts of a (1→6)-Manp polymer, (1→3)-glucan and (1→6)-glucan. Glycan microarrays allowed identification of EV surface lectin(s), while plant lectin microarray profiling revealed terminal Man and GlcNAc residues exposed at the EVs surface. Mammalian lectin microarray profiling showed that DC-SIGN receptors recognized surface carbohydrate in Paracoccidioides EVs. Our results suggest that oligosaccharides, cytoplasmic storage, and cell wall polysaccharides can be exported in fungal EVs, which also expose surface PAMPs and lectins. The role of these newly identified components in the interaction with the host remains to be unraveled.

Development of a convenient competitive ELISA for the detection of the free and protein-bound nonhuman galactosyl-α-(1,3)-galactose epitope based on highly specific chicken single-chain antibody variable-region fragments

The presence of the nonhuman galactosyl-α-(1,3)-galactose (Gal-α-(1,3)-Gal) carbohydrate epitope on a number of recombinant therapeutic proteins has recently been reported, renewing interest in this immunogenic carbohydrate epitope. It is well-known that this motif is the primary contributing factor in hyperacute rejection of porcine organ xenograft, due to the existence of natural antibodies against this epitope in human serum. Though the number of epitopes on recombinant glycoproteins may be low when compared directly to whole tissue, circulating anti-Gal-α-R immunoglobulins can still induce anaphylaxis. Therefore, there is a need for rapid and convenient methods for detection and monitoring of this epitope in biopharmaceuticals produced in recombinant mammalian systems. To this end, we have generated immune-challenged chicken single-chain antibody variable-region fragment (scFv) libraries targeting the Gal-α-(1,3)-Gal motif and have selected a panel of scFv's that bind the target. We have used one of these antibodies to develop a competitive ELISA for both free and protein-bound Gal-α-(1,3)-Gal and have demonstrated that the ELISA is specific for the target and can be used to determine the loading of the target on glycoproteins. This competitive ELISA will provide a convenient method of detecting and quantifying Gal-α-(1,3)-Gal on therapeutic glycoproteins.

Engineering mammalian mucin-type O-glycosylation in plants

Mucin-type O-glycosylation is an important post-translational modification that confers a variety of biological properties and functions to proteins. This post-translational modification has a particularly complex and differentially regulated biosynthesis rendering prediction and control of where O-glycans are attached to proteins, and which structures are formed, difficult. Because plants are devoid of GalNAc-type O-glycosylation, we have assessed requirements for establishing human GalNAc O-glycosylation de novo in plants with the aim of developing cell systems with custom-designed O-glycosylation capacity. Transient expression of a Pseudomonas aeruginosa Glc(NAc) C4-epimerase and a human polypeptide GalNAc-transferase in leaves of Nicotiana benthamiana resulted in GalNAc O-glycosylation of co-expressed human O-glycoprotein substrates. A chimeric YFP construct containing a 3.5 tandem repeat sequence of MUC1 was glycosylated with up to three and five GalNAc residues when co-expressed with GalNAc-T2 and a combination of GalNAc-T2 and GalNAc-T4, respectively, as determined by mass spectrometry. O-Glycosylation was furthermore demonstrated on a tandem repeat of MUC16 and interferon α2b. In plants, prolines in certain classes of proteins are hydroxylated and further substituted with plant-specific O-glycosylation; unsubstituted hydroxyprolines were identified in our MUC1 construct. In summary, this study demonstrates that mammalian type O-glycosylation can be established in plants and that plants may serve as a host cell for production of recombinant O-glycoproteins with custom-designed O-glycosylation. The observed hydroxyproline modifications, however, call for additional future engineering efforts.