A Giardia duodenalis gene encoding a protein with multiple repeats of a toxin homologue

Parasitology. 1995 Nov;111 ( Pt 4):423-31. doi: 10.1017/s0031182000065926.


A gene, CRP136, from the intestinal protozoan parasite Giardia duodenalis, expressed at a high level in a metronidazole-resistant line, encodes a 136 kDa protein with 23 copies of a 40 amino acid repeat. The protein is cysteine-rich and has the typical membrane-spanning region and CXXC amino acid motifs of a family of Giardia cysteine-rich surface proteins (CRSPs). The repeat unit in CRP136, shares 57% homology with the gene encoding the precursor of the sarafotoxins, a group of snake toxins from the burrowing adder known to cause symptoms similar to those of humans acutely infected with Giardia. The sarafotoxins are low molecular weight sulphydryl cross-linked peptides which are proteolytically cleaved from a precursor polyprotein. CRP136 has homology over the entire length of the sarafotoxin precursor, and the repeats are of the same length. Thus CRP136 represents the first evidence for a potential Giardia toxin. The genomic copy number of CRP136 appears to be the same in both the parent and drug-resistant lines and expression of this gene, and at least one other, is associated with a conserved partial duplication, but not amplification, of one chromosome.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antiprotozoal Agents / pharmacology
  • Base Sequence
  • Blotting, Northern
  • Blotting, Southern
  • Chromosomes
  • Drug Resistance
  • Genes, Protozoan*
  • Genomic Library
  • Giardia / genetics*
  • Metronidazole / pharmacology
  • Molecular Sequence Data
  • Multigene Family
  • Protozoan Proteins / genetics*
  • RNA, Messenger / genetics
  • Repetitive Sequences, Amino Acid*
  • Sequence Analysis, DNA
  • Sequence Homology, Amino Acid
  • Viper Venoms / genetics


  • Antiprotozoal Agents
  • CRP136 protein, Giardia duodenalis
  • Protozoan Proteins
  • RNA, Messenger
  • Viper Venoms
  • Metronidazole

Associated data

  • GENBANK/L29079