A Monoclonal Antibody to Avidin Dissociates Quaternary Structure and Curtails Biotin Binding to Avidin and Streptavidin

An anti-avidin mAb, viz., H12G4, is shown to release bound biotin in a dose-dependent manner from holoavidin and holostreptavidin and inhibit the binding of ligand to the two apoproteins. The release of biotin by this mAb is accompanied by quenching of ligand-induced enhanced fluorescence of the FITC–avidin conjugate. In terms of mechanism of release of bound biotin, we demonstrate that on binding to the Fab fragment of the mAb, the native tetrameric holoavidin undergoes dissociation progressively with time to monomers with no bound biotin associated with the latter. Based on the immunoreactivity associated with defined overlapping fragments of avidin obtained by chemical cleavage, the epitope recognized by mAb H12G4 has been localized to residues 58–96 of the primary sequence. By pepscan method of epitope mapping, this mAb is shown to identify a minimal core sequence of87RNGK90in avidin and a corresponding sequence of84RNAH87in streptavidin.