Clostridium botulinum C3 toxin

C3 exoenzyme
Structure of Clostridium botulinum C3 exoenzyme NAD from PDB entry 2C8C [1]
Identifiers
Symbol	C3
SCOP	2C89

Clostridium botulinum C3 exoenzyme is a toxin that causes the ADP-ribosylate of Rho-like proteins. Many bacterial toxins nucleotide-binding modify by ADP-ribosylation proteins involved in essential cell functions.^[2]

The molecular basis of the action of these enzymes consists in binding of nicotinamide adenine dinucleotide (NAD), splitting NAD into its ADP-ribose and nicotinamide components, and transfering the ADP-ribose moiety to a specific residue on to a protein substrate, often of eukaryotic origin. All the toxins of this family share a highly conserved glutamate, which is the catalytic residue critical for the NAD-glycohydrolase activity. ADP-ribosyltransferase toxins have distinct substrate specificities and variable pathophysiological properties and can be subdivided into four subfamilies: diphtheria-like toxins, cholera-like toxins, binary toxins and C3-like exoenzymes.

C3-like exoenzymes unlike other ADP-ribosyltransferase toxins do not require a specific cell-surface binding translocation component for cell entry. Their specificity is for the small GTP-binding proteins RhoA, RhoB, and RhoC, which are ADP-ribosylated on an asparagine residue.

1. ^ Menetrey, J., Flatau, G., Boquet, P., Menez, A., Stura, E.A. (March 2008). "Structural basis for the NAD-hydrolysis mechanism and the ARTT-loop plasticity of C3 exoenzymes.". Protein Sci. 17 (5): 878–86. PMID 18369192. 
2. ^ Moss J., Vaughan M.Russell (1990). ADP-ribosylating Toxins and G Protein, Insights into Signal Transduction. Washington, D. C.: American Society for Microbiology,.