J Biol Chem. 2012 Mar 7. [Epub ahead of print]
Galactose recognition by the apicomplexan parasite Toxoplasma gondii.
Marchant J, Cowper B, Liu Y, Lai L, Pinzan C, Marq JB, Friedrich N, Sawmynaden K, Liew L, Chai W, Childs RA, Saouros S, Simpson P, Roque Barreira MC, Feizi T, Soldati-Favre D, Matthews S.
Imperial College London, United Kingdom;
Toxosplasma gondii is the model parasite of the phylum Apicomplexa, which contains numerous obligate intracellular parasites of medical and veterinary importance, including Eimeria, Sarcocystis, Cryptosporidium, Cyclospora and Plasmodium species. Members of this phylum actively enter host cells by a multi-step process with the help of microneme protein (MIC) complexes that play important roles in motility, host cell attachment, moving junction formation and invasion. Toxoplasma gondii (Tg)MIC1-4-6 complex is the most extensively investigated microneme complex which contributes to host cell recognition and attachment via the action of TgMIC1, a sialic acid-binding adhesin. Here, we report the structure of TgMIC4 and reveal its carbohydrate-binding specificity to a variety of galactose-containing carbohydrate ligands. The lectin is composed of six apple domains in which the fifth domain displays a potent galactose-binding activity, and which is cleaved from the complex during parasite invasion. We propose that galactose recognition by TgMIC4 masks the recognition of the parasite thereby providing protection from galectin-mediated activation of the host immune system.
PMID: 22399295 [PubMed - as supplied by publisher]