S. Miyata et al., Cleavage of a C-terminal peptide is essential for heptamerization of Clostridium perfringens epsilon-toxin in the synaptosomal membrane, J BIOL CHEM, 276(17), 2001, pp. 13778-13783
Activation of Clostridium perfringens epsilon -protoxin by tryptic digestio
n is accompanied by removal of the 13 N-terminal and 22 C-terminal amino ac
id residues. In this study, we examined the toxicity of four constructs: an
epsilon -protoxin derivative (PD), in which a factor Xa cleavage site was
generated at the C-terminal trypsin-sensitive site; PD without the 13 N-ter
minal residues (DeltaN-PD); PD without the 23 C-terminal residues (DeltaC-P
D); and PD without either the N- or C-terminal residues (Delta NC-PD). A mo
use lethality test showed that DeltaN-PD was inactive, as is PD, whereas De
ltaC-PD and Delta NC-PD were equally active. DeltaC-PD and Delta NC-PD, but
not the other constructs formed a large SDS-resistant complex in rat synap
tosomal membranes as demonstrated by SDS-polyacrylamide gel electrophoresis
. When Delta NC-PD and DeltaC-PD, both labeled with P-32 and mixed in vario
us ratios, were incubated with membranes, eight distinct high molecular wei
ght bands corresponding to six heteropolymers and two homopolymers were det
ected on a SDS-polyacrylamide gel, indicating the active toxin forms a hept
americ complex. These results indicate that C-terminal processing is respon
sible for activation of the toxin and that it is essential for its heptamer
ization within the membrane.