Production of soluble Borrelia afzelii outer surface protein A in the Escherichia coli expression system

Abstract

The Borrelia burgdorferi sensu lato complex includes species that pose a growing global health challenge, with increasing reports of severe cases and fatalities, especially those linked to Borrelia afzelii in parts of Asia. Outer surface protein A (OspA), a key lipoprotein essential for tick midgut colonisation, serves as an important target for both diagnostic tools and vaccine development. This study focused on enhancing the production of soluble recombinant OspA from B. afzelii using an Escherichia coli expression system. The OspA gene from B. afzelii strain BO23 was cloned into the pET-28a(+) vector, incorporating an N-terminal His-tag, and expressed in E. coli BL21 Star (DE3). Expression was optimised by induction with 0.5 mM IPTG for five hours at 37°C in LB broth supplemented with 0.2% glucose, resulting in a yield of 5.8 mg/L of soluble OspA. Affinity chromatography achieved a purity level exceeding 90%, and the protein’s immunoreactivity was confirmed using Western blot and Dot blot assays with a commercial monoclonal antibody against OspA.