A fusion protein of the synthetic IgG-binding domain and aequorin: Expression and purification from E. coli cells and its application

•The fusion protein of ZZ domain and apoaequorin was expressed in E. coli cells.•The fusion protein was highly purified using dual-affinity chromatography.•Regenerated ZZ-aequorin exhibited similar luminescence properties to native aequorin.•ZZ-aequorin could be used as a reporter for detecting IgG (antibodies).

Aequorin is a Ca2+-binding photoprotein that is a complex of apoaequorin (apoAQ) and 2-peroxycoelenterazine. In this study, the fusion protein (ZZ-apoAQ) composed of the synthetic IgG-binding domain (ZZ domain) derived from Staphylococcus aureus protein A and apoAQ was expressed into the periplasmic space of Escherichia coli cells. ZZ-apoAQ was highly purified using Ni-chelate affinity chromatography followed by IgG affinity chromatography. ZZ-AQ was prepared from purified ZZ-apoAQ by incubation with coelenterazine and was characterized, including its luminescence properties. ZZ-AQ could be used as a reporter for detecting IgG and the measurable range of IgG coated on a 96-well plate was 1-1000 ng/mL.