title: A note on the predicted secondary structures of the active chains of cholera and diphtheria toxins.
abstract: Both the A regions of diphtheria and cholera toxins contain the site of ADP-ribosyl transferase activity which is responsible for the modification of specific target proteins in mammalian cell types. The secondary structure prediction for these A regions has been made on the basis of their recently reported primary structures. In the center of both toxin A chains, the beta-structure and alpha-helix regions alternate in a manner similar to that reported for some NAD binding proteins. Other regions of alpha-helix in the A chains may be involved in the interactions with the toxin B chains. The lack of primary structure homology between these toxins indicates that the secondary structure homology is the result of convergent evolution of a NAD binding domain in each protein.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000032:analysis*; D004167:Diphtheria Toxin / Q000032:analysis*; D009713:Nucleotidyltransferases / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases; D011487:Protein Conformation
chemical_list: D004167:Diphtheria Toxin; D002772:Cholera Toxin; D011065:Poly(ADP-ribose) Polymerases; D009713:Nucleotidyltransferases