B3(Fab)-streptavidin tetramer has higher binding avidity than B3(scFv)-streptavidin tetramer

Multivalent and multi-specific antibodies can provide valuable tools for bio-medical research, diagnosis and therapy. In antigen-antibody interactions, the avidity of antibodies depends on the affinity and the number of binding sites.¹ As artificial multivalent antibody agents, single chain Fv-streptavidin fusion tetramer proteins (scFv-SA)₄ have been previously tested.^1,2 Although, the Fab domain is known to be more stable than scFv in animal models,^3,4 it has never been used to make a multivalent agent with a streptavidin fusion. In this study, we prepared tetra-valent (Fab-cSA)₄ by fusing Fab with core streptavidin (cSA). This molecule was made using inclusion body production, refolding and chromatography purification. Affinities of the Fab-cSA tetramer and a scFv-cSA tetramer to a cell surface antigen were compared by ELISA using biotin-HRP. The Fab-cSA tetramer showed higher binding avidity than the scFv-cSA tetramer. The higher binding avidity of the Fab-cSA tetramer demonstrates its potential as a therapeutic agent for target-specific antibody therapy.