Botulinum C2 toxin ADP-ribosylates actin

Abstract

ADP-ribosylation of regulatory proteins is an important pathological mechanism by which various bacterial toxins affect eukary-otic cell functions. While diphtheria toxin catalyses the ADP-ribosylation of elongation factor 2, which results in inhibition of protein synthesis, cholera toxin and pertussis toxin ADP-ribosylate N_s and N_i respectively, the GTP-binding regulatory components of the adenylate cyclase system, thereby modulating the bidirectional hormonal regulation of the adenylate cyclase^1,2Botulinum C2 toxin is another toxin which has been reported to possess ADP-ribosyltransferase activity³. This extremely toxic agent is produced by certain strains of Clostridium botulinum⁴ and induces hypotension⁵, an increase in intestinal secretion⁶ vascular permeability⁷ and haemorrhaging in the lungs⁵. In contrast to botulinum neurotoxins, the botulinum C2 toxin apparently lacks any neurotoxic effects⁵. Here we report that botulinum C2 toxin ADP-ribosylates a protein of relative molecular mass 43,000 (43K) in intact cells and in cell-free preparations. We present evidence that the 43K protein substrate is actin, which is apparently mono-AD P-ribosylated by the toxin. Botulinum C2 toxin also ADP-ribosylated purified liver G-actin, whereas liver F-actin was only poorly ADP-ribosylated and skeletal muscle actin was not ADP-ribosylated in either its G form or its F form. ADP-ribosylation of liver G-actin by botulinum C2 toxin resulted in a drastic reduction in viscosity of actin polymerized in vitro.