Improved lectin ELISA for glycosylation analysis of biomarkers using PS-tag-fused single-chain Fv

Development of a novel and broadly applicable sandwich ELISA assay based on rabbit single-chain variable fragments and a modified Ig-binding domain of protein L fused to a polystyrene-binding peptide

Most of currently available sandwich-type enzyme-linked immunosorbent assays (ELISA) require the use of full-length animal-derived antibodies which poses welfare criticisms and are often expensive to produce. There is therefore a strong demand for the development of more affordable and animal-free methods to produce antibodies for sandwich ELISA assay. To address these issues, we propose here the development of a new technology based on two complementary rabbit single-chain variable fragments (scFvs) and an Ig-binding domain of protein L (PpL1) fused to a polystyrene-binding peptide (PS-tag) that can be recombinantly produced in bacteria. Toward this goal, we developed a rabbit scFv capable to bind the antigen via its variable regions while engaging protein L through its constant framework domain. To enhance the density of captured scFv and enable a better solvent exposure, we generated multiple PpL1 variants bearing polystyrene-binding peptides (PS) tags fused to its ends. The tandem trimer of PpL1 variant bearing PS-tags located at the N-terminus (PpL1'-T-PSN) revealed increased antigen-binding signal when immobilized on hydrophilic polystyrene (phi-PS) plates. By CDR-grafting different antigen-binding specificities into our engineered protein L-binding scFv we validated our technology against a different antigen. Finally, to further enhance the sensitivity of our assay, we implemented a protein L-based pretreatment to remove potential inhibitory immunoglobulin often present in the blood samples. The ability to rapidly and cost-effectively generate animal-free recombinant antibody fragments that can be adsorbed and specifically oriented on plates while retaining their antigen-binding properties could lead to the development of innovative and widely applicable sandwich ELISA systems for the efficient, versatile and sensitive detection of different types of antigens.

Molecularly imprinted nanoparticles for pathogen visualisation

Saccharides displayed on the cell surface of pathogens play critical roles in many activities such as adhesion, recognition and pathogenesis, as well as in prokaryotic development. In this work, we report the synthesis of molecularly imprinted nanoparticles (nanoMIPs) against pathogen surface monosaccharides using an innovative solid-phase approach. These nanoMIPs can serve as robust and selective artificial lectins specific to one particular monosaccharide. The evaluation of their binding capabilities has been implemented against bacterial cells (E. coli and S. pneumoniae) as model pathogens. The nanoMIPs were produced against two different monosaccharides: mannose (Man), which is present mainly on the surface of Gram-negative bacteria, and N-acetylglucosamine (GlcNAc) exposed on the surface of the majority of bacteria. Herein, we assessed the potential use of nanoMIPs for pathogen cell imaging and detection via flow cytometry and confocal microscopy.

Measuring fucosylated alpha-fetoprotein in hepatocellular carcinoma: A comparison of μTAS and parallel reaction monitoring

PURPOSE

Fucosylation of alpha-fetoprotein (AFP) is closely correlated with the diagnosis of patients with hepatocellular carcinoma (HCC). In current, a micro-total analysis system (μTAS) using immunoassay has been developed for determining fucosylated AFP EXPERIMENTAL DESIGN: We compared two analytical methods, μTAS and liquid chromatography-parallel reaction monitoring mass spectrometry (LC-PRM MS), for the measurement of fucosylated AFP in serum to evaluate the usefulness of the results. For this purpose, serum samples were used (cirrhosis, n = 105; HCC, n = 105), and we have discussed the analytical performance of these two methods RESULTS: We observed a correlation (R2  = 0.84) between LC-PRM MS and μTAS using samples where fucosylated levels were measured by both methods. The fucosylated level of AFP by LC-PRM MS better differentiated between cirrhosis and HCC patients than those by μTAS (AUC = 0.910 vs. 0.861), particularly in subgroups with a level of total AFP < 20 ng/mL (0.973 vs. 0.874) and in early stage (I and II) patients (0.922 vs. 0.835) CONCLUSIONS AND CLINICAL RELEVANCE: From this comparative study we can suggest that the LC-PRM MS is applicable in the measurement of fucosylated AFP from human serum and is more useful for early diagnosis of HCC.

CLINICAL RELEVANCE

Fucosylation of AFP is used for the detection of HCC. A micro-total analysis system (μTAS) has been only developed for measuring fucosylation of AFP in clinical research. This study reports the fucosylation of AFP in human serum samples from cirrhosis and HCC patients using the μTAS and a LC-PRM MS to evaluate fucosylation of AFP from each method. As a result, LC-PRM MS is complementary to the conventional μTAS method. Furthermore, LC-PRM MS provides a higher diagnostic accuracy than the μTAS in patients with low AFP levels and an early stage.

Opportunities and challenges of the tag-assisted protein purification techniques: Applications in the pharmaceutical industry

Tag-assisted protein purification is a method of choice for both academic researches and large-scale industrial demands. Application of the purification tags in the protein production process can help to save time and cost, but the design and application of tagged fusion proteins are challenging. An appropriate tagging strategy must provide sufficient expression yield and high purity for the final protein products while preserving their native structure and function. Thanks to the recent advances in the bioinformatics and emergence of high-throughput techniques (e.g. SEREX), many new tags are introduced to the market. A variety of interfering and non-interfering tags have currently broadened their application scope beyond the traditional use as a simple purification tool. They can take part in many biochemical and analytical features and act as solubility and protein expression enhancers, probe tracker for online visualization, detectors of post-translational modifications, and carrier-driven tags. Given the variability and growing number of the purification tags, here we reviewed the protein- and peptide-structured purification tags used in the affinity, ion-exchange, reverse phase, and immobilized metal ion affinity chromatographies. We highlighted the demand for purification tags in the pharmaceutical industry and discussed the impact of self-cleavable tags, aggregating tags, and nanotechnology on both the column-based and column-free purification techniques.

Direct Monitoring of Fucosylated Glycopeptides of Alpha-Fetoprotein in Human Serum for Early Hepatocellular Carcinoma by Liquid Chromatography-Tandem Mass Spectrometry with Immunoprecipitation

PURPOSE

Alpha-fetoprotein (AFP) is a widely used serological marker that is associated with hepatocellular carcinoma (HCC). Although the level of AFP is increased in HCC, its sensitivity for diagnosis is poor because AFP levels are also increased in liver diseases. Changes in glycoform, especially fucosylation, have been reported to be associated with the development of HCC.

EXPERIMENTAL DESIGN

The authors introduce the monitoring of fucosylated glycopeptides by liquid chromatography (LC)-mass spectrometry (MS) combined with immunoprecipitation, where glycan-cleaved fragments with an amino acid sequence are used as transitions. Furthermore, neuraminidase for desialylation is useful to improve the MS detection limit (limit of detection [LOD] <2 ng mL-1 ) in 0.1 μL of serum.

RESULTS

The performance of the relative percentage of fucosylated AFP (AFP-fuc%) for differentiating between early HCC and cirrhosis is better than that of serum AFP levels as indicated by a greater area under the receiver operator characteristic curve (area under the curve = 0.962 vs. 0.628) and sensitivity (92.3% vs. 53.9%), respectively. Furthermore, the inter- and intraday repeatability of AFP-fuc% in serum is less than 2.1%.

CONCLUSIONS AND CLINICAL RELEVANCE

These findings suggest that glycopeptide-based LC-MS/MS is a promising method and that AFP-fuc% is a clinically useful parameter for differentiating between early HCC and liver cirrhosis.

Glycomic Approaches for the Discovery of Targets in Gastrointestinal Cancer

Gastrointestinal (GI) cancer is the most common group of malignancies and many of its types are among the most deadly. Various glycoconjugates have been used in clinical practice as serum biomarker for several GI tumors, however, with limited diagnose application. Despite the good accessibility by endoscopy of many GI organs, the lack of reliable serum biomarkers often leads to late diagnosis of malignancy and consequently low 5-year survival rates. Recent advances in analytical techniques have provided novel glycoproteomic and glycomic data and generated functional information and putative biomarker targets in oncology. Glycosylation alterations have been demonstrated in a series of glycoconjugates (glycoproteins, proteoglycans, and glycosphingolipids) that are involved in cancer cell adhesion, signaling, invasion, and metastasis formation. In this review, we present an overview on the major glycosylation alterations in GI cancer and the current serological biomarkers used in the clinical oncology setting. We further describe recent glycomic studies in GI cancer, namely gastric, colorectal, and pancreatic cancer. Moreover, we discuss the role of glycosylation as a modulator of the function of several key players in cancer cell biology. Finally, we address several state-of-the-art techniques currently applied in this field, such as glycomic and glycoproteomic analyses, the application of glycoengineered cell line models, microarray and proximity ligation assay, and imaging mass spectrometry, and provide an outlook to future perspectives and clinical applications.

Electrochemical detection of protein glycosylation using lectin and protein–gold affinity interactions

New electrochemical method to detect glycosylation of protein using lectin and protein gold interaction.

The detection and discovery of glycan motifs in biological samples using lectins and antibodies: new methods and opportunities

Recent research has uncovered unexpected ways that glycans contribute to biology, as well as new strategies for combatting disease using approaches involving glycans. To make full use of glycans for clinical applications, we need more detailed information on the location, nature, and dynamics of glycan expression in vivo. Such studies require the use of specimens acquired directly from patients. Effective studies of clinical specimens require low-volume assays, high precision measurements, and the ability to process many samples. Assays using affinity reagents-lectins and glycan-binding antibodies-can meet these requirements, but further developments are needed to make the methods routine and effective. Recent advances in the use of glycan-binding proteins involve improved determination of specificity using glycan arrays; the availability of databases for mining and analyzing glycan array data; lectin engineering methods; and the ability to quantitatively interpret lectin measurements. Here, we describe many of the challenges and opportunities involved in the application of these new approaches to the study of biological samples. The new tools hold promise for developing methods to improve the outcomes of patients afflicted with diseases characterized by aberrant glycan expression.

Alteration of N-glycans and expression of their related glycogenes in the epithelial-mesenchymal transition of HCV29 bladder epithelial cells

The epithelial-mesenchymal transition (EMT) is an essential step in the proliferation and metastasis of solid tumor cells, and glycosylation plays a crucial role in the EMT process. Certain aberrant glycans have been reported as biomarkers during bladder cancer progression, but global variation of N-glycans in this type of cancer has not been previously studied. We examined the profiles of N-glycan and glycogene expression in transforming growth factor-beta (TGFβ)-induced EMT using non-malignant bladder transitional epithelium HCV29 cells. These expression profiles were analyzed by mass spectrometry, lectin microarray analysis, and GlycoV4 oligonucleotide microarray analysis, and confirmed by lectin histochemistry and real-time RT-PCR. The expression of 5 N-glycan-related genes were notably altered in TGFβ-induced EMT. In particular, reduced expression of glycogene man2a1, which encodes α-mannosidase 2, contributed to the decreased proportions of bi-, tri- and tetra-antennary complex N-glycans, and increased expression of hybrid-type N-glycans. Decreased expression of fuca1 gene, which encodes Type 1 α-L-fucosidase, contributed to increased expression of fucosylated N-glycans in TGFβ-induced EMT. Taken together, these findings clearly demonstrate the involvement of aberrant N-glycan synthesis in EMT in these cells. Integrated glycomic techniques as described here will facilitate discovery of glycan markers and development of novel diagnostic and therapeutic approaches to bladder cancer.

Site-specific immobilization of recombinant antibody fragments through material-binding peptides for the sensitive detection of antigens in enzyme immunoassays

The immobilization of an antibody is one of the key technologies that are used to enhance the sensitivity and efficiency of the detection of target molecules in immunodiagnosis and immunoseparation. Recombinant antibody fragments such as VHH, scFv and Fabs produced by microorganisms are the next generation of ligand antibodies as an alternative to conventional whole Abs due to a smaller size and the possibility of site-directed immobilization with uniform orientation and higher antigen-binding activity in the adsorptive state. For the achievement of site-directed immobilization, affinity peptides for a certain ligand molecule or solid support must be introduced to the recombinant antibody fragments. In this mini-review, immobilization technologies for the whole antibodies (whole Abs) and recombinant antibody fragments onto the surfaces of plastics are introduced. In particular, the focus here is on immobilization technologies of recombinant antibody fragments utilizing affinity peptide tags, which possesses strong binding affinity towards the ligand molecules. Furthermore, I introduced the material-binding peptides that are capable of direct recognition of the target materials. Preparation and immobilization strategies for recombinant antibody fragments linked to material-binding peptides (polystyrene-binding peptides (PS-tags) and poly (methyl methacrylate)-binding peptide (PMMA-tag)) are the focus here, and are based on the enhancement of sensitivity and a reduction in the production costs of ligand antibodies. This article is part of a Special Issue entitled: Recent advances in molecular engineering of antibody.

Efficient refolding and immobilization of PMMA-tag-fused single-chain Fv antibodies for sensitive immunological detection on a PMMA plate

In this study, we investigated the efficient refolding and site-specific immobilization of single-chain variable fragments (scFvs) genetically fused with a poly(methylmethacrylate)-binding peptide (PMMA-tag). According to the results of an aggregation test of a scFv-PM in the presence of 0.5 M urea, aggregation was hardly detectable at a weak-alkaline pH (8.5) with lower concentrations of NaCl. Consequently, more than 93% recovery of the anti-RNase scFv-PM model was attained, when it was refolded by dialysis against 50 mM TAPS (pH8.5). These results suggested that the apparent isoelectric point (pI) of a target scFv was decreased to a great extent by the genetic fusion of a PMMA-tag containing 5 acidic amino acids, and, thus, the solubility of the scFv-PM in its semi-denatured form was considerably improved. We also designed alternative peptide-tags composed of plural aspartic acid residues (D5, D10 and D15-tags) to decrease the apparent pI value of the fusion protein. As a consequence, scFv-D5, scFv-D10 and scFv-D15 were also efficiently refolded with yields of more than 95%. It is noteworthy that even scFv-PS-D15, which had both a positively charged polystyrene-binding peptide (PS-tag) and a negatively charged D15-tag, was serially connected at the C-terminal region of scFvs, and also refolded with a yield of 96.1%. These results clearly indicate that controlling the apparent pI value of scFvs by the fusion of oligo-peptides composed of acidic amino acids at the C-terminus resulted in a high degree of recovery via dialysis refolding. According to the results of a sandwich ELISA using scFv-PMs, scFv-D15 and scFv-PS-D15 as ligands, high antigen-binding signals were detected from both the PMMA and phi-PS plates immobilized with scFv-PMs. Furthermore, the high antigen-binding activity of scFv-PMs was maintained in an adsorption state when it was immobilized on the surface of not only PMMA, but also hydrophilic PS (phi-PS) and polycarbonate (PC). These results strongly suggested that a PMMA-tag introduced at the C-terminus of scFvs preferably recognizes ester and/or carboxyl groups exposed on the surface of plastics. The scFv-PM developed in the present study has advantages such as being a ligand antibody, compared with whole Ab and the conventional PS-tag-fused scFvs (scFv-PS), and, thus, it is considerably useful in a sandwich ELISA as well as in various immuno-detection and immuno-separation systems.

Analysis of glycan variation on glycoproteins from serum by the reverse lectin-based ELISA assay

Altered glycosylation in glycoproteins is associated with carcinogenesis, and certain glycan structures and glycoproteins are well-known markers for tumor progression. To identify potential diagnostic candidate markers, we have developed a novel method for analysis of glycosylation changes of glycoproteins from crude serum samples using lectin-based glycoprotein capture followed by detection with biotin/HRP-conjugated antibodies. The amount of lectin coated on the microplate well was optimized to achieve low background and improved S/N compared with current lectin ELISA methods. In the presence of competing sugars of lectin AAL or with sialic acid removed from the glycoproteins, we confirmed that this method specifically detects glycosylation changes of proteins rather than protein abundance variation. Using our reverse lectin-based ELISA assay, increased fucosylated haptoglobin was observed in sera of patients with ovarian cancer, while the protein level of haptoglobin remained the same between cancers and noncases. The combination of fucosylated haptoglobin and CA125 (AUC = 0.88) showed improved performance for distinguishing stage-III ovarian cancer from noncases compared with CA125 alone (AUC = 0.86). In differentiating early-stage ovarian cancer from noncases, fucosylated haptoglobin showed comparable performance to CA125. The combination of CA125 and fucosylated haptoglobin resulted in an AUC of 0.855, which outperforms CA125 to distinguish early-stage cancer from noncases. Our study provides an alternative method to quantify glycosylation changes of proteins from serum samples, which will be essential for biomarker discovery and validation studies.

Engineered nanoporous gold microspheres for stochastic sensing

Engineered nanoporous gold microsphere-based stochastic sensors detect carcynoembrionic antigen at a concentration as low as 16 ng mL⁻¹ in whole blood samples.