Purification and Preliminary Sequencing of Tc45, an Immunodominant Trypanosoma cruzi Antigen: Absence of Homology with Cruzipain, Cruzain, and a 46-Kilodalton Protein

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  • Departamento de Medicina Preventiva Animal, Facultad de Ciencias Veterinarias y Pecuarias y Departamento de Bioquimica, Facultad de Medicina, Universidad de Chile, Microbiology and Tumor Biology Center, Karolinska Institute, Ludwig Institute for Cancer Research, Biomedical Center, Uppsala Branch, Santiago, Chile

In spite of being separated by more than 20 million years of evolution, the murine and human immune systems share extensive similarities. Thus, experimental results obtained with the murine model may have predictive value for human Chagas' disease. Challenge of the H-2 congenic mouse strains A.SW (H-2s) and A.CA (H-2f) with Trypanosoma cruzi yields different results. The A.CA animals die approximately 12 days postinfection, while A.SW mice survive indefinitely. A 45-kD protein (Tc45), an antigen differentially recognized by the A.SW strain, is present in cultured epimastigotes and blood trypomastigotes. We describe here its purification from epimastigotes. The presence of Tc45 was monitored and a single band was detected. Since the molecular weights of Tc45, cruzipain, cruzain, and a 46-kD parasite polypeptide are similar, it was important to determine if these molecules are related. A complete lack of homology was observed when the sequences of cruzain, cruzipain, and the 46-kD polypeptide were compared with the preliminary sequence of Tc45.