Expression of functional single-chain variable domain fragment antibody (scFv) against mycotoxin zearalenone in Pichia pastoris

Recent Progress in Rapid Determination of Mycotoxins Based on Emerging Biorecognition Molecules: A Review

Mycotoxins are secondary metabolites produced by fungal species, which pose significant risk to humans and livestock. The mycotoxins which are produced from Aspergillus, Penicillium, and Fusarium are considered most important and therefore regulated in food- and feedstuffs. Analyses are predominantly performed by official laboratory methods in centralized labs by expert technicians. There is an urgent demand for new low-cost, easy-to-use, and portable analytical devices for rapid on-site determination. Most significant advances were realized in the field bioanalytical techniques based on molecular recognition. This review aims to discuss recent progress in the generation of native biomolecules and new bioinspired materials towards mycotoxins for the development of reliable bioreceptor-based analytical methods. After brief presentation of basic knowledge regarding characteristics of most important mycotoxins, the generation, benefits, and limitations of present and emerging biorecognition molecules, such as polyclonal (pAb), monoclonal (mAb), recombinant antibodies (rAb), aptamers, short peptides, and molecularly imprinted polymers (MIPs), are discussed. Hereinafter, the use of binders in different areas of application, including sample preparation, microplate- and tube-based assays, lateral flow devices, and biosensors, is highlighted. Special focus, on a global scale, is placed on commercial availability of single receptor molecules, test-kits, and biosensor platforms using multiplexed bead-based suspension assays and planar biochip arrays. Future outlook is given with special emphasis on new challenges, such as increasing use of rAb based on synthetic and naïve antibody libraries to renounce animal immunization, multiple-analyte test-kits and high-throughput multiplexing, and determination of masked mycotoxins, including stereoisomeric degradation products.

Affinity Biosensors for Detection of Mycotoxins in Food

This chapter reviews recent achievements in methods of detection of mycotoxins in food. Special focus is on the biosensor technology that utilizes antibodies and nucleic acid aptamers as receptors. Development of biosensors is based on the immobilization of antibodies or aptamers onto various conventional supports like gold layer, but also on nanomaterials such as graphene oxide, carbon nanotubes, and quantum dots that provide an effective platform for achieving high sensitivity of detection using various physical methods, including electrochemical, mass sensitive, and optical. The biosensors developed so far demonstrate high sensitivity typically in subnanomolar limit of detection. Several biosensors have been validated in real samples. The sensitivity of biosensors is similar and, in some cases, even better than traditional analytical methods such as ELISA or chromatography. We believe that future trends will be focused on improving biosensor properties toward practical application in food industry.

New biorecognition molecules in biosensors for the detection of toxins

Biological and synthetic recognition elements are at the heart of the majority of modern bioreceptor assays. Traditionally, enzymes and antibodies have been integrated in the biosensor designs as a popular choice for the detection of toxin molecules. But since 1970s, alternative biological and synthetic binders have been emerged as a promising alternative to conventional biorecognition elements in detection systems for laboratory and field-based applications. Recent research has witnessed immense interest in the use of recombinant enzymatic methodologies and nanozymes to circumvent the drawbacks associated with natural enzymes. In the area of antibody production, technologies based on the modification of in vivo synthesized materials and in vitro approaches with development of "display "systems have been introduced in the recent years. Subsequently, molecularly-imprinted polymers and Peptide nucleic acid (PNAs) were developed as an attractive receptor with applications in the area of sample preparation and detection systems. In this article, we discuss all alternatives to conventional biomolecules employed in the detection of various toxin molecules We review recent developments in modified enzymes, nanozymes, nanobodies, aptamers, peptides, protein scaffolds and DNazymes. With the advent of nanostructures and new interface materials, these recognition elements will be major players in future biosensor development.

Development of a single-chain variable fragment antibody-based enzyme-linked immunosorbent assay for determination of fumonisin B₁ in corn samples

BACKGROUND

Fumonisin B1 (FB1 ) is a cancer-promoting mycotoxin produced by Fusarium species and one of the major food-borne toxins in corn and corn products. The objective of this study was to produce a single-chain variable fragment (scFv) antibody for determination of FB1 in corn samples.

RESULTS

Anti-FB1 monoclonal antibodies were obtained via the hybridoma technique. Specific heavy- and light-chain variable fragments were amplified with degenerate primers and constructed into scFv antibody fragments by splice overlap extension polymerase chain reaction with linker sequences. The resulting scFv DNA fragments were cloned into the phagemid pHEN1for selection and identification of functional scFv fragment by phage display. Prokaryotic expression vector pET22b-scFv was constructed to prepare anti-FB1 scFv antibody for establishment of indirect competitive ELISA. The detection capability (CCβ) of the scFv-based ELISA was 15.00 µg kg(-1), and the limit of detection was 8.32 µg kg(-1). The recoveries and coefficients of variation were 86.74-107.34% and 9.72-14.03%, respectively. In addition, the determined results of 30 naturally contaminated corn samples by the scFv-based ELISA are in agreement with the findings of high-performance liquid chromatography (R(2) = 0.97).

CONCLUSION

This scFv-based ELISA could be used as an efficient screening method for routine monitoring the residues FB1 in corn samples.

A new zearalenone biodegradation strategy using non-pathogenic Rhodococcus pyridinivorans K408 strain

Zearalenone (hereafter referred to as ZEA) is a nonsteroidal estrogenic mycotoxin produced by several Fusarium spp. on cereal grains. ZEA is one of the most hazardous natural endocrine disrupting chemicals (EDC) which induces hyper estrogenic responses in mammals. This can result in reproductive disorders in farm animals as well as in humans. Consequently, detoxification strategies for contaminated crops are crucial for food safety. In this study we have developed a bacterial based detoxification system using a non-pathogen Rhodococcus pyridinivorans K408 strain. Following 5 days treatment of ZEA with R. pyridinivorans K408 strain HPLC analyses showed an 87.21% ZEA-degradation efficiency of the bacterial enzyme systems. In another approach, the strain biotransformation ability has also been confirmed by a bioluminescent version of the yeast estrogen screening system (BLYES), which detected an 81.75% of biodegradability of ZEA, in a good agreement with the chemical analyses. Furthermore, the capacity of R. pyridinivorans to eliminate the estrogenic effects of ZEA was tested by using an immature uterotrophic assay. Prepubertal female rats were treated with vehicle (olive oil), 17β-estradiol, ZEA (0.1-1-5-10 mg/kg body weight) and LB broth containing 500 mg/l ZEA that has already been incubated with or without Rhodococcus pyridinivorans K408 strain. Uterine weights were measured and the mRNA level changes relating to apelin, aquaporin 5, complement component 2, and calbindin-3 genes were measured by qRT-PCR. These genes represent the major pathways that are affected by estromimetic compounds. Zearalenone feeding significantly increased the uterus weight in a dose dependent manner and at the same time upregulated complement component 2 and calbindin-3 expression as well as decreased apelin and aquaporin 5 mRNA levels comparable to that seen in 17β-estradiol exposed rats. In contrast, LB broth in which ZEA was incubated with Rhodococcus pyridinivorans K408 prior to the feeding did not display any estrogenic effect neither on uterine weight nor on the expression of estrogen-regulated genes. Consequently, the identification of Rhodococcus pyridinivorans K408 strain in ZEA biodegradation proved to be a very efficient biological tool that is able to eliminate the complete estrogenic effects of ZEA. It is also remarkable that this biotransformation pathway of ZEA did not result in any residual estrogenic effects.

Functional expression of recombinant anti-BNP scFv in methylotrophic yeast Pichia pastoris and application as a recognition molecule in electrochemical sensors

Recent studies have revealed the potential of B-type natriuretic peptide (BNP) as a good prognostic marker for patients with heart failure. Antibodies against BNP are expected to be usefully employed in the diagnosis of heart failures. We established a more efficient method to produce functional anti-BNP, single chain variable fragment (scFv) using a eukaryotic expression system of Pichia pastoris. Although analysis of the N-terminal (NT) sequence of the expressed anti-BNP scFv indicated that the two Ste13 sites of the secreted anti-BNP scFv were not cleaved, the specificity of anti-BNP scFv was not affected significantly. The binding activity of anti-BNP scFv against other antigens, against four other antigens, NT probrain peptide (NT-pro BNP), atrial natriuretic peptide (ANP), carcinoembryonic antigen (CEA) and human serum albumin (HSA), was only one thousandth that of the original BNP antigen, which clearly demonstrated the specific binding of recombinant scFv toward BNP. The anti-BNP, scFv-based, electrochemical immunoassay exhibited excellent analytical performance with a detection limit of 1 fg/ml and a wide linear detection range from 1 to 10,000 fg/ml. The optimum culture conditions to obtain the maximum concentration of recombinant scFv were a pH range of 5.0-7.0 and an incubation temperature of 20°C. This anti-BNP scFv expressed in P. pastoris has the potential for promising applications in the diagnosis of heart failure.

Biochemical and biophysical characterization of humanized IgG1 produced in Pichia pastoris

The first full length IgG produced in Pichia pastoris was reported in late 1980. However, use of a wild-type Pichia expression system to produce IgGs with human-like N-linked glycans was not possible until recently. Advances in glycoengineering have enabled organisms such as Pichia to mimic human N-glycan biosynthesis and produce IgGs with human glycans on an industrial scale. Since there are only a few reports of the analytical characterization of Pichia-produced IgG, we summarize the results known in this field, and provide additional characterization data generated in our laboratories. The data suggest that Pichia-produced IgG has the same stability as that produced in Chinese hamster ovary (CHO) cells. It has similar aggregation profiles, charge variant distribution and oxidation levels as those for a CHO IgG. It contains human N-linked glycans and O-linked single mannose. Because of the comparable biophysical and biochemical characteristics, glycoengineered Pichia pastoris is an attractive expression system for therapeutic IgG productions.

Optimization of production of the anti-keratin 8 single-chain Fv TS1-218 in Pichia pastoris using design of experiments

Background

Optimization of conditions during recombinant protein production for improved yield is a major goal for protein scientists. Typically this is achieved by changing single crucial factor settings one at a time while other factors are kept fixed through trial-and-error experimentation. This approach may introduce larger bias and fail to identify interactions between the factors resulting in failure of finding the true optimal conditions.

Results

In this study we have utilized design of experiments in order to identify optimal culture conditions with the aim to improve the final yield of the anti-keratin 8 scFv TS1-218, during expression in P. pastoris in shake flasks. The effect of: pH, temperature and methanol concentration on the yield of TS1-218 using buffered minimal medium was investigated and a predictive model established. The results demonstrated that higher starting pH and lower temperatures during induction significantly increased the yield of TS1-218. Furthermore, the result demonstrated increased biomass accumulation and cell viability at lower temperatures which suggested that the higher yield of TS1-218 could be attributed to lower protease activity in the culture medium. The optimal conditions (pH 7.1, temperature 11°C and methanol concentration 1.2%) suggested by the predictive model yielded 21.4 mg TS1-218 which is a 21-fold improvement compared to the yield prior to optimization.

Conclusion

The results demonstrated that design of experiments can be utilized for a rapid optimization of initial culture conditions and that P. pastoris is highly capable of producing and secreting functional single-chain antibody fragments at temperatures as low as 11°C.

Construction of divalent anti-keratin 8 single-chain antibodies (sc(Fv)(2)), expression in Pichia pastoris and their reactivity with multicellular tumor spheroids

Single-chain variable fragments (scFvs) are small monovalent recombinant antibody fragments that retain the specificity of their parent immunoglobulins. ScFvs are excellent building blocks for new and improved immunodiagnostic and therapeutic proteins. However, the monovalency and the rapid renal elimination of scFvs result in poor tumor accumulation and retention. Engineering divalent antibody fragments is an excellent way to address these shortcomings. In this study, covalent divalent single-chain variable fragments (sc(Fv)(2)s), were constructed from the monovalent anti-keratin 8 scFvs, TS1-218 and its mutant, HE1-Q. The scFvs and sc(Fv)(2)s were expressed in the methylotrophic yeast Pichia pastoris, utilizing the alpha-factor secretion signal (α-factor) for extracellular secretion. The immunoreactivity and specificity of the antibody fragments were analyzed with enzyme-linked immunosorbent assay (ELISA) and the uptake and retention of the (125)I labeled antibody fragments were evaluated using HeLa HEp-2 multicellular tumor spheroids (MCTSs). Analysis of the antibody fragments demonstrated that parts of the α-factor remained at the N-terminal of the antibody fragments. Despite incomplete processing of the α-factor, the antibody fragments were functional where the sc(Fv)(2)s gave a three-fold stronger signal in ELISA compared to their scFv counterparts and the mutant antibodies demonstrated a stronger signal than their initial wild types. In addition, the sc(Fv)(2)s DiTS1-218 and DiHE1-Q displayed an approximately two-fold higher uptake and were retained to a larger extent in the MCTS, demonstrating a 3.9 and 9.4-fold increase in half-life respectively compared to their corresponding scFvs. In conclusion, expression in P. pastoris improved the yield 20-fold and facilitated the purification of the antibody fragments. Furthermore, the sc(Fv)(2)s presented a higher functional affinity to K 8 both in ELISA and MCTS compared to the scFvs with DiHE1-Q being the best candidate for further studies.

Selection of a single chain variable fragment antibody against ivermectin from a phage displayed library

Single chain variable fragment antibodies (scFvs) have considerable potential in immunological detection of pesticides, veterinary and other residues. In this study, a large human synthetic phage displayed library was used to select scFvs against ivermectin (IVM) by subtractive panning. After four rounds of panning, seven monoclonal phage particles capable of binding with the IVM were obtained. One of the identified novel anti-IVM scFv, hsIVM8, was expressed in Escherichia coli HB2151 and purified with Ni metal ion affinity chromatography. Sodium dodecyl sulfate polyacrylamine gel electrophoresis (SDS-PAGE) indicated that the relative molecular mass of hsIVM8 was estimated at 28 kDa. The purified hsIVM8 was used to develop a competitive indirect enzyme-linked immunosorbent assay (ci-ELISA) for IVM. The linear range of detection for standards in this ci-ELISA was approximately 0.1-5 microg/mL and 50% inhibition of control (IC(50)) was 4.11 microg/mL for IVM. These results showed promising applications of hsIVM8 for detecting IVM in agricultural and environmental matrices.

Biosensors for mycotoxin analysis: recent developments and future prospects

The toxicity and prevalence of mycotoxins in commodities and foods has necessitated the development of rapid methods in order to ensure the protection of human food and animal feed supplies. Testing for mycotoxins can be accomplished by many techniques that range from determinative tests in which the presence of the toxin is confirmed, to presumptive tests in which the presence of the toxin is inferred from the presence of markers. This review focuses on tests that fall into a third category, namely indirect assays, where the presence of the toxin is established by it's interaction with an intermediary. Such intermediaries include biological materials that bind mycotoxins, such as antibodies, as well as synthetic materials such as polymers and man-made peptides. The diversity of assays within this category is extraordinary and includes assays based upon traditional microwell formats, microbeads, membranes, electrodes, wave-guides, and solution-phase assays. The microbead format includes platforms as diverse as flow injection immunoassays, tandem column immunoassays, and immunoaffinity columns. The membrane-based formats include flow-through as well as lateral-flow assays. The electrode-based formats incorporate miniaturised immunoassays with electrochemical endpoints. The wave-guide-based devices include formats such as surface plasmon resonance, and fluorescence array biosensors, and the solution phase formats include homogeneous assays such as fluorescence polarisation immunoassay. The breadth of technologies brought to bear upon solving the need for rapid, accurate, detection of mycotoxins is impressive and includes technologies currently available commercially and those which appear poised to enter the marketplace.