Generation of AcGFP fusion with single-chain Fv selected from a phage display library constructed from mice hyperimmunized against 5-methyl 2'-deoxycytidine

The catalytic activity of a recombinant single chain variable fragment nucleic acid-hydrolysing antibody varies with fusion tag and expression host

The antigen-binding properties of single chain Fv antibodies (scFvs) can vary depending on the position and type of fusion tag used, as well as the host cells used for expression. The issue is even more complicated with a catalytic scFv antibody that binds and hydrolyses a specific antigen. Herein, we investigated the antigen-binding and -hydrolysing activities of the catalytic anti-nucleic acid antibody 3D8 scFv expressed in Escherichia coli or HEK293f cells with or without additional amino acid residues at the N- and C-termini. DNA-binding activity was retained in all recombinant forms. However, the DNA-hydrolysing activity varied drastically between forms. The DNA-hydrolysing activity of E. coli-derived 3D8 scFvs was not affected by the presence of a C-terminal human influenza haemagglutinin (HA) or His tag. By contrast, the activity of HEK293f-derived 3D8 scFvs was completely lost when additional residues were included at the N-terminus and/or when a His tag was incorporated at the C-terminus, whereas a HA tag at the C-terminus did not diminish activity. Thus, we demonstrate that the antigen-binding and catalytic activities of a catalytic antibody can be separately affected by the presence of additional residues at the N- and C-termini, and by the host cell type.

Development of an Immunoassay for Chloramphenicol Based on the Preparation of a Specific Single-Chain Variable Fragment Antibody

Specific antibodies are essential for the immune detection of small molecule contaminants. In the present study, the heavy and light variable regions (V(H )and V(L)) of the immunoglobulin genes from a hybridoma secreting a chloramphenicol (CAP)-specific monoclonal antibody (mAb) were cloned and sequenced. In addition, the light and heavy chains obtained from the monoclonal antibody were separated using SDS-PAGE and analyzed using Orbitrap mass spectrometry. The results of DNA sequencing and mass spectrometry analysis were compared, and the V(H) and V(L) chains specific for CAP were determined and used to construct a single-chain variable fragment (scFv). This fragment was recombinantly expressed as a soluble scFv-alkaline phosphatase fusion protein and used to develop a direct competitive ELISA. Compared with the parent mAb, scFv exhibits lower sensitivity but better food matrix resistance. This work highlights the application of engineered antibodies for CAP detection.

CD4 D3-binding probe: a novel fluorescence tool for detection and enumeration of CD4+ cells

A new and advanced CD4-binding reporter has been designed, produced and functionally assayed for the detection of T-helper cells.

Construction and identification of recombinant replication-defective adenovirus vector Αd/CMV/V5-DEST-TNFα-scFv

AIM: To construct a recombinant replication-defective adenovirus vector carrying TNFα-scFv and to obtain high-purity virus solution by viral packaging, purification and titration.

METHODS: The TNFα-scFv gene was amplified from the PUC57-Αmp vector and cloned into the shuttle plasmid pDONR221. The resulting pDONR221-TNFα-scFv was identified by DNA sequencing and then co-transfected into bacteria carrying the adenoviral backbone plasmid pΑd-CMV-V5-DEST to generate an adenoviral plasmid carrying TNFα-scFv (pΑd/CMV/V5-DEST-TNFα-ScFv) by homologous recombination in bacteria. After the pΑd/CMV/V5-DEST-TNFα-ScFv vector was transfected into 293 cells, the transfected 293 cells were infected with adenoviruses. The expression of TNFα-ScFv was detected by cytopathic effect and Western blot.

RESULTS: PCR amplification, restriction analysis and DNA sequencing verified that both the recombinant shuttle plasmid pDONR221-TNFα -scFv and the recombinant adenovirus vector pΑd/CMV/V5-DEST-TNFα-scFv were correctly constructed. After amplification and purification, the titer of recombinant adenovirus was 2.5×10¹¹ TCID 50/mL after proliferation in 293 cells. Western blot analysis demonstrated that TNFα-scFv was expressed efficiently in 293 cells after infection.

CONCLUSION: The recombinant adenovirus vector Αd/CMV/V5-DEST-TNFα-scFv has been successfully constructed, which lays a foundation for further study of gene function and therapy.

An assay suitable for high throughput screening of anti-influenza drugs

We developed a novel drug screening system for anti-influenza A virus by targeting the M2 proton channel. In the SPP (Single Protein Production) system, E. coli cell growth occurs only in the presence of effective M2 channel inhibitors, and thus simple measurement of cell growth was used as readouts for drug screening. Two potential inhibitors for M2 (V27A) mutant were verified using this method, which inhibit both the mutant and wild-type M2 channels.

Drop-out phagemid vector for switching from phage displayed affinity reagents to expression formats

Affinity reagents that are generated by phage display are typically subcloned into an expression vector for further biochemical characterization. This insert transfer process is time consuming and laborious especially if many inserts are to be subcloned. To simplify the transfer process, we have constructed a "drop-out" phagemid vector that can be rapidly converted to an expression vector by a simple restriction enzyme digestion with MfeI (to "drop-out" the gene III coding sequence), which generates alkaline phosphatase (AP) fusions of the affinity reagents on religation. Subsequently, restriction digestion with AscI drops out the AP coding region and religation generates affinity reagents with a C-terminal six-histidine tag. To validate the usefulness of this vector, four different human single chain Fragments of variable regions (scFv) were tested, three of which show specific binding to three zebrafish (Danio rerio) proteins, namely suppression of tumorigenicity 13, recoverin, and Ppib and the fourth binds to human Lactoferrin protein. For each of the constructs tested, the gene III and AP drop-out efficiency was between 90% and 100%. This vector is especially useful in speeding up the downstream screening of affinity reagents and bypassing the time-consuming subcloning experiments.