Fusion protein between protein ZZ and red fluorescent protein DsRed and its application to immunoassays

In the present study, a red fluorescent protein (DsRed) from the coral Discosoma was fused to the C-terminus of protein ZZ, a synthetic artificial IgG-Fc-fragment-binding protein derived from the B-domain of staphylococcal Protein A. The chimaeric protein, tagged with six histidine residues at the N-terminus, was expressed in Escherichia coli and easily purified by one-step Ni2+-chelating affinity chromatography. Its fluorescence and IgG-binding activities were validated using fluorescence-spectrum analysis, ELISA and dot-blot analysis. Furthermore, in subsequent dot-blotting immunoanalysis of glutathione S-transferase and tumour necrosis factor-alpha, and immunofluorescent microscopy assay of interferon regulatory factor 3, the chimaeric protein enabled effective detection of target molecules. Compared with fluorescence-conjugated antibodies, ZZ-DsRed is less susceptible to photobleaching and easy to produce. In addition, unlike HRP (horseradish peroxidase)-conjugated antibodies, using ZZ-DsRed needs no addition of a chromogenic reagent. Our results indicate that ZZ-DsRed shows a wide and promising application potential in immunological detection as a substitute for fluorescent or HRP-conjugated anti-IgGs.