Comparative sequence analysis of the Clostridium difficile toxins A and B

Mol Gen Genet. 1992 May;233(1-2):260-8. doi: 10.1007/BF00587587.


The six clones pTB112, pTB324, pTBs12, pCd122, pCd14 and pCd13 cover the tox locus of Clostridium difficile VPI 10463. This region of 19 kb of chromosomal DNA contains four open reading frames including the complete toxB and toxA genes. The two toxins show 63% amino acid (aa) homology, a relatedness that had been predicted by the cross-reactivity of some monoclonal antibodies (mAb) but that is in contrast to the toxin specificity of polyclonal antisera. A special feature of ToxA and ToxB is their repetitive C-termini. We define herein 19 individual CROPs (combined repetitive oligopeptides of 20-50 aa length) in the ToxB C-terminus, which are separable into five homologous groups. Comparison of the aa sequences of the N-terminal two-thirds of ToxA and ToxB revealed three marked structures, a cluster of 172 hydrophobic, highly conserved aa in the centre of both toxins, a sequence of 120 residues with an accumulation of highly conserved arginine, cysteine, histidine, methionine, and tryptophan residues, and a stretch of 248 less conserved aa. The probable function of these domains is discussed. Structural and functional homologies of ToxA and ToxB indicate that both genes have a common ancestor and may have evolved by gene duplication, with subsequent recombination and mutation, as has been reported for streptococcal glucosyltransferases (Gtf).

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Antibodies, Monoclonal
  • Bacterial Proteins*
  • Bacterial Toxins / genetics*
  • Bacterial Toxins / metabolism
  • Base Sequence
  • Blotting, Western
  • Clostridium difficile / genetics*
  • Cross Reactions
  • DNA, Bacterial
  • DNA, Recombinant / genetics
  • Enterotoxins / genetics*
  • Enterotoxins / metabolism
  • Molecular Sequence Data
  • Nucleic Acid Hybridization
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Repetitive Sequences, Nucleic Acid
  • Restriction Mapping
  • Sequence Homology, Nucleic Acid


  • Antibodies, Monoclonal
  • Bacterial Proteins
  • Bacterial Toxins
  • DNA, Bacterial
  • DNA, Recombinant
  • Enterotoxins
  • Recombinant Proteins
  • tcdA protein, Clostridium difficile
  • toxB protein, Clostridium difficile

Associated data

  • GENBANK/X60984