Hyperproduction of a bifunctional hybrid protein, metapyrocatechase-protein A, by gene fusion

Retention of functional characteristics of glutathione-S-transferase and lactate dehydrogenase-A in fusion protein

A paradigm shift toward fusion proteins to render multiple functionalities and applications on a single platform has been incurred in enzyme based diagnosis. Herein, we report development and systematic characterizations of glutathione-S-transferase (GST) and human lactate dehydrogenase A (hLDHA) in a fusion protein (GST-hLDHA) to achieve functional activities of GST and hLDHA simultaneously. The GST-pGEX-4T-2 vector system was used for cloning and purification of hLDHA, utilizing the affinity based interaction between GST and GSH in column chromatography. Bacterially purified protein was subjected to the Western blot analysis and structural analysis by circular dichroism spectroscopy, which revealed intact structural framework of the fusion construct. Kinetic characterization of the fusion GST-hLDHA protein toward GSH and NADH, suggested retention of functional activities of GST and hLDHA in fused protein as indicated by the kinetic parameters k_m and k_cat/k_m. Further analysis of effect of temperature and pH on GST-hLDHA activity revealed maximum activity around human physiological conditions (37°C and pH 8). Preservation of the structural and functional characteristics of the fusion enzyme paves the way for potential application for the detection of NADH and GSH in conjunction as biomarkers for cancer diagnosis.

Genetically Engineered Elastin-Protein A Fusion as a Universal Platform for Homogeneous, Phase-separation Immunoassay

A simple and universal platform for competitive phase-separation immunoassay is reported based on a fusion protein composed of a temperature-responsive elastin-like polypeptide (ELP) and the antibody-binding staphylococcal protein A (SpA). The basic principle is to take advantage of the ability of SpA to bind a variety of antibodies with high affinity, allowing simple separation of antigen-antibody complex by thermal precipitation. The resulting ELP-SpA fusion was shown to preserve the ability to reversibly precipitate as well as its high affinity toward different IgGs and IgMs. As a model system, a competitive phase-separation immunoassay based on the ELP-SpA format was established for paclitaxel (taxol) with IC(50) (20.18 nM) and the lower detection limit (2.94 nM) very similar to those reported for the ELISA format. Unlike the heterogeneous interaction in ELISA, which decreases the antibody-binding activity, the reported homogeneous immunoassay not only alleviates this problem but also enables the potential for high-throughput automation. We believe that the reported ELP-SpA fusion will find applications not only as a powerful diagnostic tool for diverse analytes but also a potential useful tool for purification and immobilization of antibody.

Self-assembling of glutathione S-transferase/calmodulin fusion protein on chemically modified gold surface

The fusion protein technique was used to prepare an artificial polyfunctional protein from calmodulin (CaM) and glutathione S-transferase (GST). The fusion protein was designed, expressed, and then assembled to the glutathione self-assembled gold surface. The protein assembly was confirmed through enzyme binding assay and enzyme immunoassay. Specific binding of the fusion protein to glutathione self-assembled on the gold surface was assessed via a quartz crystal microbalance (QCM). The fusion protein was reversibly adsorbed and desorbed by the competitive binding of glutathione present in a solution, thus showing that the binding of the fusion protein was specific and had a highly oriented molecular configuration.

Bioluminescent detection of RNA with sequence-specificity using RNA binding protein-luciferase fusion protein

A novel bifunctional reagent has been synthesized for RNA detection by genetic fusion of a sequence-specific RNA binding protein and firefly luciferase. The RNA binding protein used in this study recognizes the oligoribonucleotide rH4 which contains four (UUAGGG)-repeat sequence, while luciferase works as a bioluminescent marker. The constructed fusion protein exhibited both sequence-specific RNA binding and bioluminescent activities. The rH4 and rECGF, which has an unrelated sequence having the same length as rH4, were immobilized on a nylon membrane. The membrane was pre-treated by 5% bovine serum albumin and soaked into a fusion protein solution. Bioluminescent detection has successfully been performed at more than 50 pmol of rH4, so the detection limit using this protein was 50 pmol. However, no appreciable bioluminescence was induced by rECGF.

Production of the chimeric-binding protein, maltose-binding protein-protein A, by gene fusion

A fusion protein between maltose-binding protein (MBP) and staphylococcal protein A (SpA) was genetically produced. The gene fusion plasmid, pMALPA2, was constructed by inserting the protein A gene into an expression vector of maltose-binding protein in frame, and was expressed efficiently in Escherichia coli. The resulting fusion protein of molecular mass 65 kDa, retained the activity of both MBP and SpA (binding capability to amylose and immunoglobulin G). This chimeric-binding protein was used as an adhesive molecule for immobilization of antibodies to a solid-phase surface for enzyme immunoassay. An enzyme immunoassay was performed with the fusion protein, and human IgG was determined in the concentration range from 10(-4) to 10(-6) g ml-1.

Use of genetically prepared enzyme conjugates in enzyme immunoassay

Enzyme immunoassay, using enzymes crosslinked to either antibodies or antigens, has proved a valuable immunological tool for many years. Recently, gene fusion techniques have been used to prepare these enzyme conjugates. This method may be especially advantageous in cases where (1) the antigen is difficult and costly to obtain in large quantities or (2) when the activity of the marker enzyme or the affinity of the antibody or antigen is severely reduced or even destroyed by use of conventional linking methods such as chemical crosslinking. This article uses specific examples to illustrate the potential of gene fusion as a conjugation method.