Development and application of a novel recombinant Aleuria aurantia lectin with enhanced core fucose binding for identification of glycoprotein biomarkers of hepatocellular carcinoma

Lectin-glycan interactions: a comprehensive cataloguing of cancer-associated glycans for biorecognition and bio-alteration: a review

This comprehensive review meticulously compiles data on an array of lectins and their interactions with different cancer types through specific glycans. Crucially, it establishes the link between aberrant glycosylation and cancer types. This repository of lectin-defined glycan signatures, assumes paramount importance in the realm of cancer and its dynamic nature. Cancer, known for its remarkable heterogeneity and individualized behaviour, can be better understood through these glycan signatures. The current review discusses the important lectins and their carbohydrate specificities, especially recognizing glycans of cancer origin. The review also addresses the key aspects of differentially expressed glycans on normal and cancerous cell surfaces. Specific cancer types highlighted in this review include breast cancer, colon cancer, glioblastoma, cervical cancer, lung cancer, liver cancer, and leukaemia. The glycan profiles unveiled through this review hold the key to tailor-made treatment and precise diagnostics. It opens up avenues to explore the potential of targeting glycosyltransferases and glycosidases linked with cancer advancement and metastasis. Armed with knowledge about specific glycan expressions, researchers can design targeted therapies to modulate glycan profiles, potentially hampering the advance of this relentless disease.

Fucose-binding lectins: purification, characterization and potential biomedical applications

The property of lectins to specifically recognize and bind carbohydrates makes them an excellent candidate in biomedical research. Among them are fucose-binding lectins possessing the capacity to bind fucose are taxonomically, evolutionarily and ecologically significant class of lectins that are identified in a wide range of taxa. Purification of fucose-binding lectins dates back to 1967 when L-fucose binding protein from Lotus tetragonolobus was isolated using a dye that contained three α-L-fucopyranosyl residues. Beginning with that, several FBLs were purified from various animals as well as plant sources that were structurally and functionally characterised. This review focuses on fucose-binding lectins, their occurrence and purification with special emphasis on various strategies adopted to purify them followed by molecular and functional characterization. The exclusive ability to recognize and bind to fucose-containing glycans endows these lectins with the potential to act as anti-cancer agents, diagnostic markers and mitogens for immune cells. Though they have been in research focus for more than half a century with their occurrence reported in various taxa, they still need to be explored for their prospective functions to develop them as a biological tool in biomedical research.

Fucosylation of HLA-DRB1 regulates CD4+ T cell-mediated anti-melanoma immunity and enhances immunotherapy efficacy

Immunotherapy efficacy is limited in melanoma, and combinations of immunotherapies with other modalities have yielded limited improvements but also adverse events requiring cessation of treatment. In addition to ineffective patient stratification, efficacy is impaired by paucity of intratumoral immune cells (itICs); thus, effective strategies to safely increase itICs are needed. We report that dietary administration of L-fucose induces fucosylation and cell surface enrichment of the major histocompatibility complex (MHC)-II protein HLA-DRB1 in melanoma cells, triggering CD4+ T cell-mediated increases in itICs and anti-tumor immunity, enhancing immune checkpoint blockade responses. Melanoma fucosylation and fucosylated HLA-DRB1 associate with intratumoral T cell abundance and anti-programmed cell death protein 1 (PD1) responder status in patient melanoma specimens, suggesting the potential use of melanoma fucosylation as a strategy for stratifying patients for immunotherapies. Our findings demonstrate that fucosylation is a key mediator of anti-tumor immunity and, importantly, suggest that L-fucose is a powerful agent for safely increasing itICs and immunotherapy efficacy in melanoma.

FUT8 is regulated by miR-122-5p and promotes malignancies in intrahepatic cholangiocarcinoma via PI3K/AKT signaling

BACKGROUND

Intrahepatic cholangiocarcinoma (iCCA) is the second-most lethal primary liver cancer and its prognosis remains dismal. N-glycosylation, which is biosynthesized by a number of glycosyltransferases, plays an important role in a variety of biological processes and is associated with cancer development and progression.

METHODS

Based on our previous proteogenomic resources from an iCCA cohort of 262 patients, fucosyltransferases 8 (FUT8) showed significant prognosis relevance in iCCA. Tumor tissues from iCCA patients were used to evaluate the correlation between its expression and clinical information. Gain/loss-of-function experiments in iCCA cell lines were performed to elucidate the biological function of FUT8. In addition, its downstream pathways and post-transcriptional regulators were inferred and verified.

RESULTS

Elevated FUT8 expression was clinically associated with worse overall survival in iCCA patients. Its overexpression promoted migration, invasion and proliferation ability of iCCA cells. In addition, miR-122-5p was found to act as a post-transcriptional regulator of FUT8 and proved to inhibit FUT8 expression and then suppress the proliferation and migration ability of iCCA cell lines. Furthermore, FUT8 was observed to promote iCCA development through PI3K/AKT signaling pathway.

CONCLUSIONS

These findings demonstrated that FUT8, regulated by miR-122-5p, could be a tumor promoter of iCCA through PI3K/AKT signaling pathway.

Mass Spectrometry-Based Glycoproteomic Workflows for Cancer Biomarker Discovery

Glycosylation has a clear role in cancer initiation and progression, with numerous studies identifying distinct glycan features or specific glycoproteoforms associated with cancer. Common findings include that aggressive cancers tend to have higher expression levels of enzymes that regulate glycosylation as well as glycoproteins with greater levels of complexity, increased branching, and enhanced chain length1. Research in cancer glycoproteomics over the last 50-plus years has mainly focused on technology development used to observe global changes in glycosylation. Efforts have also been made to connect glycans to their protein carriers as well as to delineate the role of these modifications in intracellular signaling and subsequent cell function. This review discusses currently available techniques utilizing mass spectrometry-based technologies used to study glycosylation and highlights areas for future advancement.

Abnormal B cell glycosylation in autoimmunity: A new potential treatment strategy

Systemic lupus erythematosus (SLE) and primary Sjögren’s syndrome (pSS) are two autoimmune diseases characterised by the production of pathogenic autoreactive antibodies. Their aetiology is poorly understood. Nevertheless, they have been shown to involve several factors, such as infections and epigenetic mechanisms. They also likely involve a physiological process known as glycosylation. Both SLE T cell markers and pSS-associated autoantibodies exhibit abnormal glycosylation. Such dysregulation suggests that defective glycosylation may also occur in B cells, thereby modifying their behaviour and reactivity. This study aimed to investigate B cell subset glycosylation in SLE, pSS and healthy donors and to extend the glycan profile to serum proteins and immunoglobulins. We used optimised lectin-based tests to demonstrate specific glycosylation profiles on B cell subsets that were specifically altered in both diseases. Compared to the healthy donor B cells, the SLE B cells exhibited hypofucosylation, whereas only the pSS B cells exhibited hyposialylation. Additionally, the SLE B lymphocytes had more galactose linked to N-acetylglucosamine or N-acetylgalactosamine (Gal-GlcNAc/Gal-GalNAc) residues on their cell surface markers. Interestingly, some similar alterations were observed in serum proteins, including immunoglobulins. These findings indicate that any perturbation of the natural glycosylation process in B cells could result in the development of pathogenic autoantibodies. The B cell glycoprofile can be established as a preferred biomarker for characterising pathologies and adapted therapeutics can be used for patients if there is a correlation between the extent of these alterations and the severity of the autoimmune diseases.

Novel Combined Enzymatic Approach to Analyze Nonsialylated N-Linked Glycans through MALDI Imaging Mass Spectrometry

Alterations to N-glycan expression are relevant to the progression of various diseases, particularly cancer. In many cases, specific N-glycan structural features such as sialylation, fucosylation, and branching are of specific interest. A novel MALDI imaging mass spectrometry workflow has been recently developed to analyze these features of N-glycosylation through the utilization of endoglycosidase enzymes to cleave N-glycans from associated glycoproteins. Enzymes that have previously been utilized to cleave N-glycans include peptide-N-glycosidase F (PNGase F) to target N-glycans indiscriminately and endoglycosidase F3 (Endo F3) to target core fucosylated N-glycans. In addition to these endoglycosidases, additional N-glycan cleaving enzymes could be used to target specific structural features. Sialidases, also termed neuraminidases, are a family of enzymes that remove terminal sialic acids from glycoconjugates. This work aims to utilize sialidase, in conjunction with PNGase F/Endo F3, to enzymatically remove sialic acids from N-glycans in an effort to increase sensitivity for nonsialylated N-glycan MALDI-IMS peaks. Improving detection of nonsialylated N-glycans allows for a more thorough analysis of specific structural features such as fucosylation or branching, particularly of low abundant structures. Sialidase utilization in MALDI-IMS dramatically increases sensitivity and increases on-tissue endoglycosidase efficiency, making it a very useful companion technique to specifically detect nonsialylated N-glycans.

Intranasal Delivery of BACE1 siRNA and Rapamycin by Dual Targets Modified Nanoparticles for Alzheimer's Disease Therapy

Alzheimer's disease (AD), as a progressive and irreversible brain disorder, remains the most universal neurodegenerative disease. No effective therapeutic methods are established yet due to the hindrance of the blood-brain barrier (BBB) and the complex pathological condition of AD.  Therefore, a multifunctional nanocarrier (Rapa@DAK/siRNA) for AD treatment is constructed to achieve small interfering RNA of β-site precursor protein (APP) cleaving enzyme-1 (BACE1 siRNA) and rapamycin co-delivery into the brain, based on Aleuria aurantia lectin (AAL) and β-amyploid (Aβ)-binding peptides (KLVFF) modified PEGylated dendrigraft poly-l-lysines (DGLs) via intranasal administration. Nasal administration provides an effective way to deliver drugs directly into the brain through the nose-to-brain pathway. AAL, specifically binding to L-fucose located in the olfactory epithelium, endows Rapa@DAK/siRNA with high brain entry efficiency through intranasal administration. KLVFF peptide as an Aβ targeting ligand and aggregation inhibitor enables nanoparticles to bind with Aβ, inhibit Aβ aggregation, and reduce toxicity. Meanwhile, the release of BACE1 siRNA and rapamycin is confirmed to reduce BACE1 expression, promote autophagy, and reduce Aβ deposition. Rapa@DAK/siRNA is verified to improve the cognition of transgenic AD mice after intranasal administration. Collectively, the multifunctional nanocarrier provides an effective and potential intranasal avenue for combination therapy of AD.

Targeting cell surface glycans with lectin-coated fluorescent nanodiamonds

Glycosylation is arguably the most important functional post-translational modification in brain cells and abnormal cell surface glycan expression has been associated with neurological diseases and brain cancers. In this study we developed a novel method for uptake of fluorescent nanodiamonds (FND), carbon-based nanoparticles with low toxicity and easily modifiable surfaces, into brain cell subtypes by targeting their glycan receptors with carbohydrate-binding lectins. Lectins facilitated uptake of 120 nm FND with nitrogen-vacancy centers in three types of brain cells - U87-MG astrocytes, PC12 neurons and BV-2 microglia cells. The nanodiamond/lectin complexes used in this study target glycans that have been described to be altered in brain diseases including sialic acid glycans via wheat (Triticum aestivum) germ agglutinin (WGA), high mannose glycans via tomato (Lycopersicon esculentum) lectin (TL) and core fucosylated glycans via Aleuria aurantia lectin (AAL). The lectin conjugated nanodiamonds were taken up differently by the various brain cell types with fucose binding AAL/FNDs taken up preferentially by glioblastoma phenotype astrocyte cells (U87-MG), sialic acid binding WGA/FNDs by neuronal phenotype cells (PC12) and high mannose binding TL/FNDs by microglial cells (BV-2). With increasing recognition of glycans having a role in many diseases, the lectin bioconjugated nanodiamonds developed here are well suited for further investigation into theranostic applications.

Research advances and prospects of legume lectins

Lectins are widely distributed proteins having ability of binding selectively and reversibly with carbohydrates moieties and glycoconjugates. Although lectins have been reported from different biological sources, the legume lectins are the best-characterized family of plant lectins. Legume lectins are a large family of homologous proteins with considerable similarity in amino acid sequence and their tertiary structures. Despite having strong sequence conservation, these lectins show remarkable variability in carbohydrate specificity and quaternary structures. The ability of legume lectins in recognizing glycans and glycoconjugates on cells and other intracellular structures make them a valuable research tool in glycomic research. Due to variability in binding with glycans, glycoconjugates and multiple biological functions, legume lectins are the subject of intense research for their diverse application in different fields such as glycobiology, biomedical research and crop improvement. The present review specially focuses on structural and functional characteristics of legume lectins along with their potential areas of application.

Towards structure-focused glycoproteomics

Facilitated by advances in the separation sciences, mass spectrometry and informatics, glycoproteomics, the analysis of intact glycopeptides at scale, has recently matured enabling new insights into the complex glycoproteome. While diverse quantitative glycoproteomics strategies capable of mapping monosaccharide compositions of N- and O-linked glycans to discrete sites of proteins within complex biological mixtures with considerable sensitivity, quantitative accuracy and coverage have become available, developments supporting the advancement of structure-focused glycoproteomics, a recognised frontier in the field, have emerged. Technologies capable of providing site-specific information of the glycan fine structures in a glycoproteome-wide context are indeed necessary to address many pending questions in glycobiology. In this review, we firstly survey the latest glycoproteomics studies published in 2018–2020, their approaches and their findings, and then summarise important technological innovations in structure-focused glycoproteomics. Our review illustrates that while the O-glycoproteome remains comparably under-explored despite the emergence of new O-glycan-selective mucinases and other innovative tools aiding O-glycoproteome profiling, quantitative glycoproteomics is increasingly used to profile the N-glycoproteome to tackle diverse biological questions. Excitingly, new strategies compatible with structure-focused glycoproteomics including novel chemoenzymatic labelling, enrichment, separation, and mass spectrometry-based detection methods are rapidly emerging revealing glycan fine structural details including bisecting GlcNAcylation, core and antenna fucosylation, and sialyl-linkage information with protein site resolution. Glycoproteomics has clearly become a mainstay within the glycosciences that continues to reach a broader community. It transpires that structure-focused glycoproteomics holds a considerable potential to aid our understanding of systems glycobiology and unlock secrets of the glycoproteome in the immediate future.

Research advances and prospects of legume lectins

Lectins are widely distributed proteins having ability of binding selectively and reversibly with carbohydrates moieties and glycoconjugates. Although lectins have been reported from different biological sources, the legume lectins are the best-characterized family of plant lectins. Legume lectins are a large family of homologous proteins with considerable similarity in amino acid sequence and their tertiary structures. Despite having strong sequence conservation, these lectins show remarkable variability in carbohydrate specificity and quaternary structures. The ability of legume lectins in recognizing glycans and glycoconjugates on cells and other intracellular structures make them a valuable research tool in glycomic research. Due to variability in binding with glycans, glycoconjugates and multiple biological functions, legume lectins are the subject of intense research for their diverse application in different fields such as glycobiology, biomedical research and crop improvement. The present review specially focuses on structural and functional characteristics of legume lectins along with their potential areas of application.

NF-κB Signaling Is Regulated by Fucosylation in Metastatic Breast Cancer Cells

A growing body of evidence indicates that the levels of fucosylation correlate with breast cancer progression and contribute to metastatic disease. However, very little is known about the signaling and functional outcomes that are driven by fucosylation. We performed a global proteomic analysis of 4T1 metastatic mammary tumor cells in the presence and absence of a fucosylation inhibitor, 2-fluorofucose (2FF). Of significant interest, pathway analysis based on our results revealed a reduction in the NF-κB and TNF signaling pathways, which regulate the inflammatory response. NF-κB is a transcription factor that is pro-tumorigenic and a prime target in human cancer. We validated our results, confirming that treatment of 4T1 cells with 2FF led to a decrease in NF-κB activity through increased IκBα. Based on these observations, we conclude that fucosylation is an important post-translational modification that governs breast cancer cell signaling.

New Enzymatic Approach to Distinguish Fucosylation Isomers of N-Linked Glycans in Tissues Using MALDI Imaging Mass Spectrometry

Specific alterations in N-linked glycans, such as core fucosylation, are associated with many cancers and other disease states. Because of the many possible anomeric linkages associated with fucosylated N-glycans, determination of specific anomeric linkages and the site of fucosylation (i.e., core vs outer arm) can be difficult to elucidate. A new MALDI mass spectrometry imaging workflow in formalin-fixed clinical tissues is described using recombinant endoglycosidase F3 (Endo F3), an enzyme with a specific preference for cleaving core-fucosylated N-glycans attached to glycoproteins. In contrast to the broader substrate enzyme peptide-N-glycosidase F (PNGaseF), Endo F3 cleaves between the two core N-acetylglucosamine residues at the protein attachment site. On tissues, this results in a mass shift of 349.137 a.m.u. for core-fucosylated N-glycans when compared to N-glycans released with standard PNGaseF. Endo F3 can be used singly and in combination with PNGaseF digestion of the same tissue sections. Initial results in liver and prostate tissues indicate core-fucosylated glycans associated to specific tissue regions while still demonstrating a diverse mix of core- and outer arm-fucosylated glycans throughout all regions of tissue. By determining these specific linkages while preserving localization, more targeted diagnostic biomarkers for disease states are possible without the need for microdissection or solubilization of the tissue.

Structure and engineering of tandem repeat lectins

Through their ability to bind complex glycoconjugates, lectins have unique specificity and potential for biomedical and biotechnological applications. In particular, lectins with short repeated peptides forming carbohydrate-binding domains are not only of high interest for understanding protein evolution but can also be used as scaffold for engineering novel receptors. Synthetic glycobiology now provides the tools for engineering the specificity of lectins as well as their structure, multivalency and topologies. This review focuses on the structure and diversity of two families of tandem-repeat lectins, that is, β-trefoils and β-propellers, demonstrated as the most promising scaffold for engineering novel lectins.

Core-Fucosylated Tetra-Antennary N-Glycan Containing A Single N-Acetyllactosamine Branch Is Associated with Poor Survival Outcome in Breast Cancer

(1) Glycoproteins account for ~80% of proteins located at the cell surface and in the extracellular matrix. A growing body of evidence indicates that α-L-fucose protein modifications contribute to breast cancer progression and metastatic disease. (2) Using a combination of techniques, including matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) based in cell and on tissue imaging and glycan sequencing using exoglycosidase analysis coupled to hydrophilic interaction ultra-high performance liquid chromatography (HILIC UPLC), we establish that a core-fucosylated tetra-antennary glycan containing a single N-acetyllactosamine (F(6)A4G4Lac1) is associated with poor clinical outcomes in breast cancer, including lymph node metastasis, recurrent disease, and reduced survival. (3) This study is the first to identify a single N-glycan, F(6)A4G4Lac1, as having a correlation with poor clinical outcomes in breast cancer.

Biomarker analysis of fucosylated kininogen through depletion of lectin reactive heterophilic antibodies in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) accounts for >700,000 deaths worldwide, largely related to poor rates of diagnosis. Our previous work identified glycoproteins with increased levels of fucosylation in HCC. Plate-based assays to measure this change were compromised by increased levels of heterophilic antibodies with glycan lacking terminal galactose residues, which allowed for increased binding to the lectins used in these assays. To address this issue, we developed a multi-step protein A/G incubation and filtration method to remove the contaminating signal. However, this method was time consuming and expensive so alternative methods were desired. Herein, we describe a simple method relying on PEG precipitation that allows for the removal of IgG and IgM but retention of glycoproteins of interest. This method was tested on three sample sets, two internal and one external. PEG depletion of heterophilic IgG and IgM reduced in the coefficient of variation as observed with the protein A/G filtration method from 26.82% to 7.50% and allowed for the measurement of fucosylated protein. This method allowed for the measurement of fucosylated kininogen, which could serve as a biomarker of HCC. In conclusion, a new and simple method for the depletion of heterophilic IgG and IgM was developed and allowed for the analysis of fucosylated kininogen in patients with liver disease.

Mass Spectrometry Approaches to Glycomic and Glycoproteomic Analyses

Glycomic and glycoproteomic analyses involve the characterization of oligosaccharides (glycans) conjugated to proteins. Glycans are produced through a complicated nontemplate driven process involving the competition of enzymes that extend the nascent chain. The large diversity of structures, the variations in polarity of the individual saccharide residues, and the poor ionization efficiencies of glycans all conspire to make the analysis arguably much more difficult than any other biopolymer. Furthermore, the large number of glycoforms associated with a specific protein site makes it more difficult to characterize than any post-translational modification. Nonetheless, there have been significant progress, and advanced separation and mass spectrometry methods have been at its center and the main reason for the progress. While glycomic and glycoproteomic analyses are still typically available only through highly specialized laboratories, new software and workflow is making it more accessible. This review focuses on the role of mass spectrometry and separation methods in advancing glycomic and glycoproteomic analyses. It describes the current state of the field and progress toward making it more available to the larger scientific community.

N-Linked Glycan Branching and Fucosylation Are Increased Directly in Hcc Tissue As Determined through in Situ Glycan Imaging

Hepatocellular carcinoma (HCC) remains as the fifth most common cancer in the world and accounts for more than 700,000 deaths annually. Changes in serum glycosylation have long been associated with this cancer but the source of that material is unknown and direct glycan analysis of HCC tissues has been limited. Our laboratory previously developed a method of in situ tissue based N-linked glycan imaging that bypasses the need for microdissection and solubilization of tissue prior to analysis. We used this methodology in the analysis of 138 HCC tissue samples and compared the N-linked glycans in cancer tissue with either adjacent untransformed or tissue from patients with liver cirrhosis but no cancer. Ten glycans were found significantly elevated in HCC tissues as compared to cirrhotic or adjacent tissue. These glycans fell into two major classes, those with increased levels of fucosylation and those with increased levels of branching with or without any fucose modifications. In addition, increased levels of fucosylated glycoforms were associated with a reduction in survival time. This work supports the hypothesis that the increased levels of fucosylated N-linked glycans in HCC serum are produced directly from the cancer tissue.

Analytical Application of Lectins

This review is devoted to the analytical application of carbohydrate-binding proteins called lectins. The nature of lectins and the regularities of their specificity with respect to simple sugars and complex carbohydrate-containing biomolecules are discussed. The main areas of the modern analytical application of lectins are described. Lectin-affinity chromatography, histo- and cytochemical approaches, lectin blotting, microarray, and biosensor technologies as well as microplate analysis are considered in detail. Data on the use of lectins for the detection of cells and microorganisms as well as the study of protein glycosylation are summarized. The large potential of lectins as components of analytical systems used for the identification of glycans and the characteristics of their structure are substantiated.

Functional Expression and Characterization of the Recombinant N-Acetyl-Glucosamine/N-Acetyl-Galactosamine-Specific Marine Algal Lectin BPL3

Lectins, characterized by their carbohydrate-binding ability, have extensive practical applications. However, their industrial use is limited due to impurity. Thus, quality-controlled production of recombinant lectin is necessary. In this study, the algal lectin BPL3 (Bryopsis plumosa lectin 3) was successfully produced using a bacterial expression system, BL21(DE3), with an artificial repeated structure (dimeric construct). Recombinant dimeric BPL3 (rD2BPL3) was confirmed by LC-MS/MS spectrometry. Expression efficiency was greater for the construct with the repeat structure (rD2BPL3) than the monomeric form (rD1BPL3). Optimal conditions for expression were 1 mM IPTG at 20 °C. Recombinant lectin was purified under denaturing conditions and refolded by the flash dilution method. Recombinant BPL3 was solubilized in 1× PBS containing 2 M urea. rD2BPL3 showed strong hemagglutination activity using human erythrocyte. rD2BPL3 had a similar sugar specificity to that of the native protein, i.e., to N-acetyl-glucosamine (GlcNAc) and N-acetyl-galactosamine (GalNAc). Glycan array results showed that recombinant BPL3 and native BPL3 exhibited different binding properties. Both showed weak binding activity to α-Man-Sp. Native BPL3 showed strong binding specificity to the alpha conformation of amino sugars, and rD2BPL3 had binding activity to the beta conformation. The process developed in this study was suitable for the quality-controlled large-scale production of recombinant lectins.

Identification of Plasma Membrane Glycoproteins Specific to Human Glioblastoma Multiforme Cells Using Lectin Arrays and LC-MS/MS

Glioblastoma, also known as glioblastoma multiforme (GBM), is the most malignant type of brain cancer and has poor prognosis with a median survival of less than one year. While the structural changes of tumor cell surface carbohydrates are known to be associated with invasive behavior of tumor cells, the cell surface glycoproteins to differentiate the low- and high-grade glioma cells can be potential diagnostic markers and therapeutic targets for GBMs. In the present study, lectin arrays consisting of eight lectins were employed to explore cell surface carbohydrate expression patterns on low-grade oligodendroglioma cells (Hs683) and GBM cells (T98G). Griffonia simplicifolia I (GS I) was found to selectively bind to T98G cells and not to Hs683 cells. For identification of the glioblastoma-specific cell surface markers, the glycoproteins from each cell type were captured by a GS I lectin column and analyzed by LC-MS/MS. The identified proteins from the two cell types were quantified using label-free quantitative analysis based on spectral counting. Of cell surface glycoproteins showing significant increases in T98G cells, five proteins were selected for verification of both protein and glycosylation level changes using Western blot and GS I lectin-based immunosorbent assay.

Influence of Trp flipping on carbohydrate binding in lectins. An example on Aleuria aurantia lectin AAL

Protein-carbohydrate interactions are very often mediated by the stacking CH-π interactions involving the side chains of aromatic amino acids such as tryptophan (Trp), tyrosine (Tyr) or phenylalanine (Phe). Especially suitable for stacking is the Trp residue. Analysis of the PDB database shows Trp stacking for 265 carbohydrate or carbohydrate like ligands in 5 208 Trp containing motives. An appropriate model system to study such an interaction is the AAL lectin family where the stacking interactions play a crucial role and are thought to be a driving force for carbohydrate binding. In this study we present data showing a novel finding in the stacking interaction of the AAL Trp side chain with the carbohydrate. High resolution X-ray structure of the AAL lectin from Aleuria aurantia with α-methyl-l-fucoside ligand shows two possible Trp side chain conformations with the same occupation in electron density. The in silico data shows that the conformation of the Trp side chain does not influence the interaction energy despite the fact that each conformation creates interactions with different carbohydrate CH groups. Moreover, the PDB data search shows that the conformations are almost equally distributed across all Trp-carbohydrate complexes, which would suggest no substantial preference for one conformation over another.

Marine Lectins DlFBL and HddSBL Fused with Soluble Coxsackie-Adenovirus Receptor Facilitate Adenovirus Infection in Cancer Cells BUT Have Different Effects on Cell Survival

Cancer development and progression are usually associated with glycosylation change, providing prognostic and diagnostic biomarkers, as well as therapeutic targets, for various cancers. In this work, Dicentrarchus labrax fucose binding lectin (DlFBL) and Haliotis discus discus sialic acid binding lectin (HddSBL) were genetically fused with soluble coxsackie-adenovirus receptor (sCAR), and produced through a bacterial expression system. Results showed that recombinant sCAR-DlFBL not only facilitated adenovirus Ad-EGFP infection in K562/ADR and U87MG cells, but also enhanced the cytotoxicity of adenovirus harboring gene encoding Pinellia pedatisecta agglutinin (PPA) or DlFBL (Ad-PPA or Ad-DlFBL) on U87MG cells through inducing apoptosis. Recombinant sCAR-HddSBL facilitated Ad-EGFP infection, but dramatically counteracted the cytotoxicity of both Ad-PPA and Ad-DlFBL in U87MG cells. Further analysis revealed that sCAR-HddSBL, but not sCAR-DlFBL, significantly upregulated transcription factor E2F1 levels in U87MG cells, which might be responsible for the adverse effect of sCAR-HddSBL on Ad-PPA and Ad-DlFBL. Taken together, our data suggested that sCAR-DlFBL could be further developed to redirect therapeutic adenoviruses to infect cancer cells such as U87MG, and the sCAR-lectin fusion proteins for adenoviral retargeting should be carefully examined for possible survival signaling induced by lectins, such as HddSBL.