Neutralizing monoclonal antibody specific for Naja nigricollis toxin .alpha.: preparation, characterization and localization of the antigenic binding site

Abstract

One homogeneous population of high-affinity monoclonal antibodies (KD = 0.35 nM) specific for N. nigricollis toxin .alpha. [a neurotoxin] was produced. It neutralizes the biological activty of the toxin under both in vivo and in vitro conditions. The molecular zone of the toxin to which the antibody binds was precisely defined on the basis of cross-reaction experiments using 5 derivatives of toxin .alpha. monomodified at a single amino group and 2 naturally ocurring homologous toxins. The epitope is located at the base of the first .beta.-sheet loop of the toxin, involving the 2 positive charges at the N-terminal position and lysine-15, proline-18 and probably threonine-16. This region is topographically distinct from the toxic site of toxin .alpha.. Several possibilities are offered to explain the mechanism(s) of specific neutralization.