Enhancement and Analysis of Human Antiaflatoxin B1 (AFB1) scFv Antibody-Ligand Interaction Using Chain Shuffling

Generation of a highly specific recombinant full-length antibody for detecting ethirimol in fruit and environmental water

High-performance antibodies are core reagents for highly sensitive immunoassays. Herein, based on a novel hapten, a hybridoma secreting the high-affinity anti-ethirimol monoclonal antibody (mAb-14G5F6) was isolated with an IC50 value of 1.35 μg/L and cross-reactivity below 0.20% for 13 analogs. To further address the challenge of hybridoma preservation and antibody immortalization, a recombinant full-length antibody (rAb-14G5F6) was expressed using the HEK293(F) expression system based on the mAb-14G5F6 gene. The affinity, specificity, and tolerance of rAb-14G5F6, as characterized by indirect competitive enzyme-linked immunosorbent assay and noncompetitive surface plasmon resonance, exhibited high concordance with those of mAb-14G5F6. Further immunoassays based on rAb-14G5F6 were developed for irrigation water and strawberry fruit with limits of detection of 0.0066 and 0.036 mg/kg, respectively, recoveries of 80100%, and coefficients of variation below 10%. Furthermore, homology simulation and molecular docking revealed that GLU(L40), GLY(L107), GLY(H108), and ASP(H114) play important roles in forming hydrogen bonds and pi-anion ionic bonds between rAb-14G5F6 and ethirimol, resulting in the high specificity and affinity of rAb-14G5F6 for ethirimol, with a KD of 5.71 × 10-10 mol/L. Overall, a rAb specific for ethirimol was expressed successfully in this study, laying the groundwork for rAb-based immunoassays for monitoring fungicide residues in agricultural products and the environment.

Overview-gold nanoparticles-based sensitive nanosensors in mycotoxins detection

Food-borne mycotoxins is one of the food safety concerns in the world. At present, nanosensors are widely used in the detection and analysis of mycotoxins due to their high specificity and sensitivity. In nanosensor-based mycotoxindetections, the sensitivity is mainly improved from two aspects. On the one hand, based on the principle of immune response, antigens and antibodies can be modified and developed. Such as single-domain heavy chain antibodies, aptamers, peptides, and antigen mimotopes. On the other hand, improvements and innovations have been made on signal amplification materials, including gold nanoparticles (AuNPs), quantum dots, and graphene, etc. Among them, gold nanoparticles can not only be used as a signal amplification material, but also can be used as carriers for identification elements, which can be used for signal amplification in detection. In this article, we systematically summarized the emerging strategies for enhancing the detection sensitivity of traditional gold nanoparticles-based nanosensors, in terms of recognition elements and signal amplification. Representative examples were selected to illustrate the potential mechanism of each strategy in enhancing the colorimetric signal intensity of AuNP and its potential application in biosensing. Finally, our review suggested the challenges and future prospects of gold particles in detection of mycotoxins.

A novel immunosensor based on cobalt oxide nanocomposite modified single walled carbon nanohorns for the selective detection of aflatoxin B1

We developed a novel, sensitive, and selective platform for the specific determination of aflatoxin B1 (AFB1). Single-walled carbon nanohorns decorated by a cobalt oxide composite and gold nanoparticles were created to provide facile electron transfer and improve the sensor's sensitivity. In addition, we attributed the selectivity of the proposed sensor to the specific binding property of the anti-aflatoxin B1 antibody. We clarified the specific interaction of the proposed immunosensor to AFB1 using homology modeling combined with molecular docking. In the presence of AFB1, the current signal of the modified electrode reduced; this involved specific antibody-antigen binding, including hydrophobic hydrogen bonding and pi-pi stack interactions. The new AFB1 sensor platform showed two linearity ranges of 0.01-1 ng mL^-1 and 1-100 ng mL^-1, with the limit of detection at 0.0019 ng mL^-1. We investigated the proposed immunosensor in real samples, including peanuts, certified reference material of a peanut sample (labeled 206 μg kg^-1 AFB1), corn, and chicken feed. The sensor's accuracy was 86.1-104.4% recovery, which agrees with the reference HPLC technique using paired t-test analysis. The present work shows excellent performance for AFB1 detection and could be applied for food quality control or modified to detect other mycotoxins.

Targeting acute myeloid cell surface using a recombinant antibody isolated from whole-cell biopanning of a phage display human scFv antibody library

To discover new therapeutic antibodies for treatment of acute myeloid leukemia (AML) without the requirement of a known antigen, a human single-chain variable fragment (scFv) library was used to isolate novel antibody fragments recognizing HL-60 AML cells. After three rounds of biopanning, scFv-expressing phages were selected to test for binding to the target cell by flow cytometry. The clone with highest binding specificity to HL-60 cells (designated y1HL63D6) was further investigated. Fluorescent staining indicated that y1HL63D6 scFv bound to a target located on the cell surface. Whole immunoglobulin, IgG-y1HL63D6 was then generated and tested for the binding against bone marrow mononuclear cells (BMMCs) from AML patients. Significantly higher fluorescent signals were observed for some patient samples when compared to normal BMMCs or non-AML patients' BMMCs. Next, the IgG-y1HL63D6 format was tested for antibody-dependent cell cytotoxicity (ADCC). The results demonstrated that IgG-y1HL63D6 but not the control antibody, trastuzumab, could mediate specific killing of HL-60 target cells. In conclusion, our results indicate that specific antibodies can be isolated by biopanning whole cells with a non-immunized human scFv antibody phage display library and that the isolated antibody against HL-60 cells showed therapeutic potential.

Single-chain fragment variable produced by phage display technology: Construction, selection, mutation, expression, and recent applications in food safety

Immunoassays are reliable, efficient, and accurate methods for the analysis of small-molecule harmful substances (such as pesticides, veterinary drugs, and biological toxins) that may be present in food. However, traditional polyclonal and monoclonal antibodies are limited by animal hosts and hinder further development of immunoassays. With the gradual application of phage display technology as an efficient in vitro selection technology, the single-chain fragment variable (scFv) now provides an exciting alternative to traditional antibodies. Efficiently constructed scFv source libraries and specifically designed biopanning schemes can now yield scFvs possessing specific recognition capabilities. A rational mutation strategy further enhances the affinity of scFv, and allows it to reach a level that cannot be achieved by immunization. Finally, appropriate prokaryotic expression measures ensure stable and efficient production of scFv. Therefore, when developing excellent scFvs, it is necessary to focus on three key aspects of this process that include screening, mutation, and expression. In this review, we analyze in detail the preparation and affinity improvement process for scFv and provide insights into the research progress and development trend of scFv-based immunoassay methods for monitoring small-molecule harmful substances.

Preparation and application of a specific single-chain variable fragment against artemether

Artemether, an artemisinin derivative, is a component of the commonly used artemisinin-based combination therapy, artemether-lumefantrine. In this study, we cloned the VH and VL genes of a cell line (mAb 2G12E1) producing a monoclonal antibody specific to artemether, and used to construct a recombinant DNA of single-chain variable fragment (scFv). The scFv was constructed into prokaryotic expression vectors pET32a (+), pET22b (+), pGEX-2T, and pMAL-p5x, respectively. However, only the pMAL-p5x/scFv could be induced to express soluble scFv with comparable sensitivity and specificity to that of mAb 2G12E1. Based on the anti-artemether scFv, an indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed. The 50% of inhibition concentration (IC₅₀) value and the working range based on IC₂₀ to IC₈₀ were 4.33 ng mL^-1 and 1.05-22.65 ng mL^-1, respectively. The artemether content in different drugs were determined by the developed icELISA, and the results were consistent to those determined by ultra performance liquid chromatography (UPLC). The anti-artemether scFv prepared in the current study could be a valuable genetically engineered antibody applied for artemether monitoring and specific binding mechanism studying.

Camelization of a murine single-domain antibody against aflatoxin B1 and its antigen-binding analysis

Aflatoxin B1 (AFB1), a highly toxic mycotoxin, always contaminated in a variety of agricultural products. Camelid variable domain of heavy chain antibody (VHH) is a noteworthy reagent in immunoassay, owing to its excellent characteristics. Immunization of camelid animals is a straightforward strategy to produce VHHs. In this study, to avoid the dependence on the large animals, the camelized, murine antibody (cVHs) against AFB1 was prepared in vitro based on the identities between murine VH and camelid VHH and then to develop an immunoassay for AFB1. A murine anti-AFB1 VH fragment (VH-2E6) was selected for camelization through replacement of conserved hydrophobic residues in framework region 2 (FR2) (cVH-FR2), point mutation at position 103 in the FR4 region (cVH-103), and CDR3-grafted with a high AFB1-affinity VHH (cVH-Nb26). The cVH-Nb26 had a yield of 5 mg/L as refolded protein expressed from Escherichia coli and 10 mg/L expressed from Pichia pastoris. Compared with anti-AFB1 single-chain fragment variable (scFv) 2E6, cVH-Nb26 performed more than 20-fold enhancement of AFB1-binding interactions. Although the AFB1-affinity of cVH-Nb26 cannot meet the application requirement in the present form, our study provides effective strategies for preparation of camelized antibody in vitro, which could be a promising immunoreagent for AFB1 detection.

Application of Recombinant Human scFv Antibody as a Powerful Tool to Monitor Nitrogen Fixing Biofertilizer in Rice and Legume

Bradyrhizobium is an endophytic bacterium under investigation as an efficient biofertilizer for sustainable legume-rice rotational cropping system. Monitoring and bio-imaging of this nitrogen fixing bacterium is essential for the study of plant-microbe evolution, soil microbiome, as well as quality control in organic farming. While phage display antibody technology has been widely used to generate recombinant antibody for myriad medical purposes, so far, this technology has been minimally applied in the agricultural sector. In this study, single-chain variable fragments (scFv) against two Bradyrhizobium strains SUTN9-2 (yiN92-1e10) and DOA9 (yiDOA9-162) were isolated from a human phage display antibody library. Specific binding of scFv was demonstrated by ELISA and confocal-immunofluorescence imaging techniques. Bradyrhizobium localization in both endophytic and bacteroid forms could be observed inside rice tissue and plant nodule, respectively. Moreover, successful application of the recombinant antibody for the evaluation of nodule occupancy was also demonstrated in comparison with standard GUS-staining method. The results of this study showed for the first time the potential use of human phage display scFv antibody for imaging and monitoring of Bradyrhizobium biofertilizer and thus could be further applied for point-of-detection of bacterial inoculum in the legume-rice rotational crop system.

IMPORTANCE Human scFv antibody generated from phage display technology was successfully used for the generation of specific recombinant antibodies: yiN92-1e10 and yiDOA9-162 for the detection of Bradyrhizobium strains SUTN9-2 and DOA9, respectively. These two recombinant scFv antibodies could be used for precise detection of the rhizobia both in symbiosis with legume and endophyte in rice tissue by ELISA and immunofluorescent staining, during legume-rice rotational cropping system in the field. This methodology can be further employed for the study of other plant-microbe interactions and monitoring of biofertilizer in diverse sustainable cropping systems as well as in precision agriculture.

Mimotopes for Mycotoxins Diagnosis Based on Random Peptides or Recombinant Antibodies from Phage Library

Mycotoxins, the small size secondary metabolites of fungi, have posed a threat to the safety of medicine, food and public health. Therefore, it is essential to create sensitive and effective determination of mycotoxins. Based on the special affinity between antibody and antigen, immunoassay has been proved to be a powerful technology for the detection of small analytes. However, the tedious preparation and instability of conventional antibodies restrict its application on easy and fast mycotoxins detection. By virtue of simplicity, ease of use, and lower cost, phage display library provides novel choices for antibodies or hapten conjugates, and lead random peptide or recombinant antibody to becoming the promising and environmental friendly immune-reagents in the next generation of immunoassays. This review briefly describes the latest developments on mycotoxins detection using M13 phage display, mainly focusing on the recent applications of phage display technology employed in mycotoxins detection, including the introduction of phage and phage display, the types of phage displayed peptide/recombinant antibody library, random peptides/recombinant antibodies-based immunoassays, as well as simultaneous determination of multiple mycotoxins.

Generation, selection and modification of anti-cardiac troponin I antibodies with high specificity and affinity

Current diagnosis of acute myocardial infarction involves quantification of circulating cTn levels. This work endeavoured to generate and enhance recombinant antibody fragments targeting various epitopes on the N- and C-terminals of the cTnI molecule, thereby facilitating highly sensitive detection of the troponin molecule. From this approach, two anti-cTnI scFv antibodies were successfully selected using either phage display or structural reformatting of full length anti-cTnI IgG. Their antibody binding affinity was further optimised via chain shuffling and/or site directed mutagenesis, resulting in scFv with heightened sensitivity when compared to the wild-type scFv. If used in conjunction with existing anti-mid fragment cTnI antibodies, these N- and C- terminal-targeting scFvs show high potential for the enhancement of current cTnI detection assays by limiting the effects from cTnI degradation or troponin complex formation.

Binding Characteristic of Various Antibody Formats Against Aflatoxins

The application of recombinant antibodies for the analysis of foods and food contaminants is now a major focus, given their capacity to be engineered to tailor their specificity, enhance their stability, and modify their structural formats to fit the desired analytical platform. In this study, human scFv antibody fragments generated against aflatoxin B1 (AFB1) were selected as the model antibody to explore the effect of antibody formats on their binding activity and to evaluate their potential use as immunoreagents for food contaminant analysis. Four human scFv antibody fragments against aflatoxin B1 (AFB1), previously isolated and engineered by chain shuffling, were converted into various formats, that is, scFv-AP fusions, scFv-Fc, and whole IgG molecules. The result indicated that the effects of the antibody format on the binding property varied, depending on the sequence of scFv. For all of the scFv clones, the scFv-AP fusion format showed the highest sensitivity by competitive ELISA, while the effects on the binding activity after conversion to scFv-Fc or IgG format varied, depending on the amino acid sequence of the antibodies. The sAFH-3e3 antibodies that showed the best performance by competitive ELISA were selected for further investigation. The sAFH-3e3 was converted to the scFv-GFP format and tested by fluorescence-linked immunosorbent assay (FLISA), which showed that its binding property was equivalent to those of scFv-Fc and IgG formats. The potential applications of the sAFH-3e3 in a rapid test kit format based on ELISA (scFv-AP) and in a lateral flow immunochromatography assay (LFIA) (IgG) were demonstrated. A comparison of methods for the extraction of AFB1 from matrices for use with these assay formats indicated that PBS and TBST are better than 70% methanol.

Recombinant antibodies and their use for food immunoanalysis

Antibodies are widely employed as biorecognition elements for the detection of a plethora of compounds including food and environmental contaminants, biomarkers, or illicit drugs. They are also applied in therapeutics for the treatment of several disorders. Recent recommendations from the EU on animal protection and the replacement of animal-derived antibodies by non-animal-derived ones have raised a great controversy in the scientific community. The application of recombinant antibodies is expected to achieve a high growth rate in the years to come thanks to their versatility and beneficial characteristics in comparison to monoclonal and polyclonal antibodies, such as stability in harsh conditions, small size, relatively low production costs, and batch-to-batch reproducibility. This review describes the characteristics, advantages, and disadvantages of recombinant antibodies including antigen-binding fragments (Fab), single-chain fragment variable (scFv), and single-domain antibodies (V_HH) and their application in food analysis with especial emphasis on the analysis of biotoxins, antibiotics, pesticides, and foodborne pathogens. Although the wide application of recombinant antibodies has been hampered by a number of challenges, this review demonstrates their potential for the sensitive, selective, and rapid detection of food contaminants.

Microcystin-LR heterologous genetically engineered antibody recombinant and its binding activity improvement and application in immunoassay

Microcystin-LR (MC-LR) is a high-toxic biohazard that pollutes ecological environment and agroproducts. In this study, a newly recombined genetically engineered antibody (AV_HH-MV_H) with higher thermal stability and binding activity was designed by chain shuffling and based on our previously obtained anti-MC-LR scFv and nanobody. Based on AV_HH-MV_H template, a capacity of 8.99 × 10⁵ CFU/mL of phage display AV_HH-MV_H mutagenesis library was constructed by site-directed mutagenesis in MV_H-CDR3 region, and then used for ultrasensitive mutants screening. Afterwards, a total of five positive AV_HH-MV_H mutants were isolated from the mutagenesis library, and their binding activity was higher than AV_HH-MV_H for MC-LR. The AV_HH-MV_H mutant 3 was cloned into pET-25b vector for soluble expression, and the concentration of target protein expressed in culture system was 43.5 mg/L. An indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) was established based on purified AV_HH-MV_H mutant 3 protein, and it showed ultrasensitive binding activity for MC-LR with the detection limit of 0.0075 μg/L, which was far below the maximum residue limit standard of 1.0 μg/L in drinking water proposed by World Health Organization. The established IC-ELISA shows good accuracy, repeatability, stability and applicability for MC-LR spiked samples, and it is promising for MC-LR ultrasensitive monitoring.

Human Hexa-Histidine-Tagged Single-Chain Variable Fragments for Bioimaging of Bacterial Infections

The single-chain variable fragment (scFv) of monoclonal antibodies is a promising recombinant nanostructure for various medical applications, including bioimaging and targeted therapy. While numerous scFv antibodies against eukaryotic cell surface proteins (especially cancer biomarkers) have been generated and engineered to suit various purposes, only a few specific scFv against bacterial cell surfaces have been developed, especially those of human origin. Recent incidents of emerging multidrug-resistant pathogenic bacteria and the realization of the importance of a balanced microbiota on the health of the host has led to more interests in the development of recombinant antibacterial antibodies as a detection probe or targeted therapy for bacterial infections. This study reports the generation of two specific human antibacterial scFv using phage display antibody technology. The recombinant scFv fragments of about 30 kDa and a diameter of 5 nm were produced and purified from engineered Escherichia coli that can enhance cytosolic disulfide bond formation. As a proof of principle, Propionibacterium acnes and Pseudomonas aeruginosa were used as model Gram-positive and Gram-negative bacteria, respectively. Specificity at the strain and species level to both planktonic and biofilm forms of these bacteria were demonstrated in various assay formats, namely, ELISA, flow cytometry, western blot, immunofluorescence, and electron microscopy via the hexa-histidine tag. This recombinant scFv generation platform can be applied for other bacteria, and since the scFv obtained has a benefit of being a human origin, it could be conveniently engineered for various therapeutic or theranostic applications with minimized adverse immunoreaction.

Site-directed mutations of anti-amantadine scFv antibody by molecular dynamics simulation: prediction and validation

A recombinant single-chain variable fragment (scFv) antibody was produced from a hybridoma cell strain secreting the monoclonal antibody for amantadine (AMD), and then its recognition mechanisms for AMD were studied using the molecular docking and molecular dynamics. Complex dockings revealed that three regions are involved in antibody recognition; framework 2 of the VL chain (LFR2) GLU40 and TYR42, complementarity-determining region of the VL chain (LCDR3) TYR116, and framework 2 of the VH chain (HFR2) HIS40 and TRP52 were the key amino acid residues. The results of molecular dynamics show that the most important amino acid residues in the interaction between AMD and scFv are HIS40 and TYR116. On the basis of the results of virtual mutation, the scFv antibody was evolved by directional mutagenesis of amino acid residue GLY107 to PHE. Indirect competitive ELISA (icELISA) results indicated that the scFv mutant had highly increased affinity for AMD with up to 3.9-fold improved sensitivity. Thus, the scFv antibody can be applied for mechanistic studies of intermolecular interactions, and our work offered affinity maturated antibodies by site mutations, which were beneficial for valuable anti-AMD antibody design and preparation in future.

Electrochemical Immuno- and Aptasensors for Mycotoxin Determination

Modern analysis of food and feed is mostly focused on development of fast and reliable portable devices intended for field applications. In this review, electrochemical biosensors based on immunological reactions and aptamers are considered in the determination of mycotoxins as one of most common contaminants able to negatively affect human health. The characteristics of biosensors are considered from the point of view of general principles of bioreceptor implementation and signal transduction providing sub-nanomolar detection limits of mycotoxins. Moreover, the modern trends of bioreceptor selection and modification are discussed as well as future trends of biosensor development for mycotoxin determination are considered.