The carboxy-terminal C2-like domain of the alpha-toxin from Clostridium perfringens mediates calcium-dependent membrane recognition

The lethal, cytolytic alpha-toxin (phospholipase C) of Clostridium perfringens consists of two distinct modules: the larger N-terminal domain catalyses phospholipid hydrolysis, and its activity is potentiated by a smaller C-terminal domain. Calcium ions are essential for the binding of alpha-toxin to lipid films. Sixteen alpha-toxin variants with single amino acid substitutions in the C-terminal region were obtained using site-directed mutagenesis and T7 expression technology. Five of these variants showed reduced phospholipase C activity and were considerably less active than native alpha-toxin under calcium-limiting conditions. Replacement of Thr-272 by Pro diminished phospholipase C activity, severely affected haemolysis and platelet aggregation and perturbed a surface-exposed conformational epitope. The results of sequence comparisons and molecular modelling indicate that the C-terminal region probably belongs to the growing family of C2 beta-barrel domains, which are often involved in membrane interactions, and that the functionally important substitutions are clustered at one extremity of the domain. The combined findings suggest that the C-terminal region of alpha-toxin mediates interactions with membrane phospholipids in a calcium-dependent manner. Mutations to this domain may account for the natural lack of toxicity of the alpha-toxin homologue, phospholipase C of Clostridium bifermentans.


Published in:
Molecular microbiology, 26, 5, 867-76
Year:
1998
ISSN:
0950-382X
Keywords:
Other identifiers:
Laboratories:




 Record created 2010-09-07, last modified 2018-03-17


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