Glycobiology, 2001, Vol. 11, No. 7 541-547
© 2001 Oxford University Press
Toxoplasma gondii micronemal protein MIC1 is a lactose-binding lectin
2Departamento de Biologia Celular e Molecular e Bioagentes Patogênicos, Faculdade de Medicina de Ribeirão Preto, USP, Av. Bandeirantes 3900, 14049-900, Ribeirão Preto, SP, Brazil, 3Pós-graduação em Imunologia Básica e Aplicada, Universidade de São Paulo, Ribeirão Preto, SP 14049-900, Brazil, 4Centro de Química de Proteínas, Universidade de São Paulo, Ribeirão Preto, SP 14049-900, Brazil, 5Departamento de Ginecologia e Obstetrícia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP 14049-900, Brazil, 6Instituto de Ciências Biomédicas, Universidade Federal de Uberlândia, Uberlândia, MG 38400-902, Brazil, and 7Departamento de Bioquímica, Universidade Federal de São Paulo, São Paulo, SP 04044-020, SP, Brazil.
Host cell invasion by Toxoplasma gondii is a multistep process with one of the first steps being the apical release of micronemal proteins that interact with host receptors. We demonstrate here that micronemal protein 1 (MIC1) is a lactose-binding lectin. MIC1 and MIC4 were recovered in the lactose-eluted (Lac+) fraction on affinity chromatography on immobilized lactose of the soluble antigen fraction from tachyzoites of the virulent RH strain. MIC1 and MIC4 were both identified by N-terminal microsequencing. MIC4 was also identified by sequencing cDNA clones isolated from an expression library following screening with mouse polyclonal anti-60/70 kDa (Lac+ proteins) serum. This antiserum localized the Lac+ proteins on the apical region of T. gondii tachyzoites by confocal microscopy. The Lac+ fraction induced hemagglutination (mainly type A human erythrocytes), which was inhibited by ß-galactosides (3 mM lactose and 12 mM galactose) but not by up to 100 mM melibiose (
-galactoside), fucose, mannose, or glucose or 0.2 mg/ml heparin. The lectin activity of the Lac+ preparation was attributed to MIC1, because blotted MIC1, but not native MIC4, bound human erythrocyte type A and fetuin. The copurification of MIC1 and MIC4 may have been due to their association, as reported by others. These data suggest that MIC1 may act through its lectin activity during T. gondii infection.
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