Characterisation of alpha-1 giardin: an immunodominant Giardia lamblia annexin with glycosaminoglycan-binding activity

Int J Parasitol. 2003 Oct;33(12):1341-51. doi: 10.1016/s0020-7519(03)00201-7.


Alpha-1 giardin is an immunodominant protein in the intestinal protozoan parasite Giardia lamblia. The Triage((R)) parasite panel, used to detect copro-antigens in stool from giardiasis patients, reacts with an epitope between amino acids 160 and 200 in alpha-1 giardin. This region of the protein is also highly immunogenic during human infections. Alpha-1 giardin is related to annexins and like many other annexins it was shown to be plasma membrane associated. Immunoelectron and immunofluorescence microscopy revealed that some alpha-1 giardin are displayed on the surface of recently excysted cells. Recombinant alpha-1 giardin displayed a Ca(2+)-dependent binding to glycosaminoglycans (GAGs), in particular heparan sulphate, a common GAG in the intestinal tract. Recombinant alpha-1 giardin bound to thin sections of human small intestine, a binding which could be inhibited by adding increasing concentrations of sulphated sugars. A surface associated trypsin activated Giardia lectin (taglin) has been suggested to be important for G. lamblia attachment. In this study we show that a monoclonal antibody that inhibits taglin recognises alpha-1 and alpha-2 giardin. Thus, alpha-1 giardin is a highly immunoreactive GAG-binding protein, which may play a key role in the parasite-host interaction. Our results further show a conserved function of annexins from lower to higher eukaryotes.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Antigens, Protozoan / analysis*
  • Antigens, Protozoan / metabolism
  • Giardia lamblia / chemistry*
  • Giardiasis / immunology*
  • Giardiasis / metabolism
  • Heparitin Sulfate / metabolism
  • Host-Parasite Interactions
  • Humans
  • Intestinal Mucosa / metabolism
  • Microscopy, Fluorescence
  • Microscopy, Immunoelectron
  • Oocysts / chemistry*
  • Protein Binding
  • Recombinant Proteins / metabolism


  • Antigens, Protozoan
  • Recombinant Proteins
  • Heparitin Sulfate