In this study, nano-sized bacterial magnetic particles (BMPs) displaying human estrogen receptor ligand binding domain (ERLBD) on the surface was successfully produced by the magnetic bacterium, Magnetospirillum magneticum AMB-1. Furthermore, a non-isotopic binding assay for estrogenic compounds using the BMPs displaying ERLBD was developed. A BMP membrane-specific protein, Mms16, was used as an anchor molecule to localize ERLBD on the surface of BMPs. ERLBD-BMP complexes were simply extracted by magnetic separation from ruptured AMB-1 transformants and used for the assay based on the competitive binding of alkaline phosphatase conjugated 17β-estradiol (ALP-E2) as a tracer. Dissociation constant of the receptor was 2.3 nM. Inhibition curves were evaluated by the decrease in luminescence intensity resulting from the enzymatic reaction of alkaline phosphatase. The overall simplicity of this receptor binding assay results in a method that can be easily adapted to a high throughput format. Moreover, this method can be integrated into a fully-automated ligand screening system using magnetic separation.
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