Induction of a phosphomannosyl binding lectin activity in Giardia

Abstract

Giardia lamblia, a protozoan parasite that causes widespread diarrheal disease, expresses a surface membrane associated lectin, taglin, which is specifically activated by limited proteolysis with trypsin, a protease that is present in abundance at the site of infection. When activated, taglin agglutinates enterocytes which are the cells to which the parasite adheres in vivo, and in addition, binds to isolated brush border membranes of these cells. These findings suggest that this lectin may be involved in the host-parasite interaction. Taglin is most specific for terminal phosphomannosyl residues and its binding to red cells is mediated by cell surface phosphate residues. Hemagglutinating activity induced by taglin is most active at pH 6.5 and is dependent on divalent cations. A monoclonal antibody to taglin reacts with the surface membrane of live trophozoites and recognizes a protein of 28/30 kDa in lysates of Giardia trophozoites, by immunoblotting. This finding is confirmed by direct demonstration of lectin activity by erythrocyte binding to proteins electroblotted to nitrocellulose, which revealed specific red cell binding to giardial protein bands in the same molecular weight range as those recognized by the monoclonal antibody.

A New Family of Giardial Cysteine-Rich Non-VSP Protein Genes and a Novel Cyst Protein

“…Because of the large size of HCNCp, transfer buffer contained 20% MeOH/0.1% SDS. Blotted proteins were blocked overnight in PBST (PBS+0.05% Tween 20) containing 5% milk, probed in rabbit anti-AU1 antibody (1/5,000 in PBST/0.1% milk; Bethyl Laboratories, Montgomery, TX) or antibody to the constitutive protein taglin (1/700 in PBST/0.1% milk; loading control; [77]) for 1.5 hr, washed 3× over 30 min in PBST, incubated in Zymax goat anti-rabbit (1/8,000; Zymed Laboratories/Invitrogen) or Zymax goat anti-mouse (1/5,000; Zymed Laboratories/Invitrogen) antibodies for 1 hr, washed 3× in PBST over 30 min, and developed in ECL (Amersham Biosciences, Piscataway, NJ).…”

Secretory protein trafficking in Giardia intestinalis

“…One exception is a putatively GPI‐anchored protein, termed GP49 (Das et al ., 1991; 1994), the status of which remains unclear, however, because its sequence shows a transmembrane region including a 54‐amino‐acid cytoplasmic tail, which is unusual for a GPI‐anchored protein. Another surface‐associated and thus secreted protein is the phosphomannosyl‐specific lectin, taglin (Ward et al ., 1990), a 28/30 kDa molecule with a mode of attachment to the plasma membrane that has not been determined yet. Other lectins that are at least partially displayed on the trophozoite surface include the giardins, which also display annexin functions (Bauer et al ., 1999; Weiland et al ., 2003).…”

Glycobiology of Parasites: Role of Carbohydrate–Binding Proteins and Their Ligands in the Host–Parasite Interaction

“…This was suggested by the finding that amebic cytolysis of CHO cells could be blocked by Gal and GalNAc as well as 6 Giardiasis I 407 and the abundance of glycoconjugates in the glycocalyx coat and microvillus membrane of intestinal cells supports the involvement of lectincarbohydrate interactions in the recognition and adhesion trophozoites to host cells. Lectins with specificity for mannosyl and phosphomannosyl residues have been described in Giardia (Farthing et al, 1986;Lev et al, 1986;Ward et al, 1990). by anti-lectin antibodies (Ravdin, 1981;Saffer and Petri, 1991).…”