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A Recombinant scFv/Streptavidin-Binding Peptide Fusion Protein for the Quantitative Determination of the Scorpion Venom Neurotoxin AahI

Abstract We created a construct encoding a peptide known to mimic the binding properties of biotin fused to the carboxyterminus of a scFv fragment that binds a scorpion toxin (AahI). This fusion protein was produced in the periplasm of bacteria and purified to homogeneity by singlestep affinity chromatography on streptavidinagarose with a yield close to 1 mg/l. DNA sequencing, dot blot and mass spectrometric analyses demonstrated the integrity of the soluble immunoconjugate. Fusion to the streptavidinbinding peptide did not affect the ability of the scFv to recognize its antigen with a high affinity (Kd = 2.3x 1010M). Similarly, the streptavidinbinding property was not impaired in the fusion protein. Thus, the immunoconjugate was bifunctional and had a low molecular mass of 28 kDa. This enabled us to develop rapid and sensitive immunoassays for the specific detection of the toxin AahI accurately to 0.6 ng/ml, opening up new perspectives for the diagnosis of envenomations.