CBMs display great variation in substrate binding affinity and specificity, what makes them particularly suitable molecules to explore innovative uses where immobilization of proteins in insoluble carbohydrates is sought. Here, recent developments on biotechnological and biomedical applications of a starch binding domain (SBD) are presented.
First, the SBD was used as a tag for fusion protein purification (SBDtag). We generated four recombinant proteins and developed a protein purification system to isolate the fusion proteins using affinity chromatography with an immobilized starch analog. Furthermore, raw starches from different sources were effectively used for protein purification.
As we observed that the starch immobilized proteins are more stable to pH and resistant to proteases than the soluble proteins, we proved a novel application; the use the SBDtag to immobilize antigens on starch granules to use the system for the oral administration of vaccine candidates. We found the system allows for and facilitates antigen capture in the sites of immune induction in murine model, as measured by the response induction without the use of any adjuvant. In addition, the response is modulated depending on the antigen or protein fused to the SBDtag and the route of administration. This work therefore is a proof-of concept demonstrating the potential of the SBDtag system.