title: The amino-acid sequence of two non-toxic mutants of diphtheria toxin: CRM45 and CRM197.
abstract: The amino-acid sequences of two diphtheria toxin-related, non-toxic proteins, CRM45 and CRM197 , were deduced from the complete sequence of their genes: tox 45 and tox 197. CRM45 lacks the last 149 C-terminal amino-acid residues, but is otherwise identical to diphtheria toxin: a single C----T transition introduces an "ochre" (TAA) termination signal in tox 45, after the codon for threonine-386. A single G----A transition was also found in tox 197, leading to the substitution of glycine-52, present in the wild-type toxin, with glutamic acid in CRM197 . This aminoacid change is responsible for the loss of the NAD:EF2 ADP-ribosyltransferase activity in CRM197 , due most probably to an alteration of the NAD+ binding site.
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003353:Corynebacterium diphtheriae / Q000235:genetics; D003429:Cross Reactions; D004167:Diphtheria Toxin / Q000235:genetics*; D005796:Genes; D005798:Genes, Bacterial; D009154:Mutation
chemical_list: D001426:Bacterial Proteins; C033445:CRM45 fragment of diphtheria toxin; D004167:Diphtheria Toxin; C028581:CRM197 (non-toxic variant of diphtheria toxin)