Depolymerization of Actin Filaments Induces Polymerization of Microtubules

摘要

Botulinum C_2 toxin (C2T) elaborated by certain strains of Clostridium botulinum types C andD is composed of two dissimilar protein components, components I (49.4 kDa) and II (80.5 kDa),which are associated with neither covalent nornoncovalent bond. These two components individually have little activity, but together act as apotent toxin. Component I of the toxin catalyzes ADP-ribosylation of nonmuscle, but notmuscle, actin monomers and inactivates theirpolymerization abilities. By exposing culturedcells to C2T, component I enters into the cellsthrough the binding site induced by trypsinactivated component II and causes a rounding ofcells due to the modification of intracellularactin monomers and thereby disintegration ofactin filaments. However, these morphologicalchanges in cultured cells have been observedwith the adherent cells, of which morphology ispartly restricted by the contact to the substratum. In the present study, therefore, the authorattemped to see whether any changes occur inmorphology of the cells cultured in suspension,of which shape is free from the restriction byadhesive contact to the culture plate.