Caracterização de antígenos componentes de complexos ribonucleoprotéicos de Trypanosoma cruzi contendo seqüências com repetições de aminoácidos

Abstract

Trypanosoma cruzi expresses several proteins containing highly antigenic amino acid repeats. Here we characterized TcRpL7a and TcRBP28, which carry similar repeat motifs and share homology to the eukaryotic L7a ribosomal protein and to a T. brucei RNA binding protein, respectively. Analyses of the full length and truncated recombinant TcRpL7a showed that the humoral response of patients with Chagas disease is directed towards its repetitive domain. Sequence analyses of copies of TcRpL7a genes present in the genome of six T. cruzi strains indicate that the number of repeats is higher in T. cruzi II than in T. cruzi I strains. A serum panel of 59 patients showed that 73% reacted with TcRpL7a, 71% reacted with TcRBP28 and 80% reacted with 1:1 mixture of both antigens. Synthetic peptide harboring the TcRpL7a repeat motif reacted with 46% of chagasic sera. Antibodies raised against both antigens identified equivalent amounts of the native proteins in all three stages of the parasite life cycle. Analyses of subcellular fractions indicated that TcRBP28 is present in the cytoplasm whereas TcRpL7a co-fractionates with polysomes. Confirming their predicted cellular localization, GFP fusions showed that, whereas GFP::TcRBP28 localizes in the cytoplasm, GFP::TcRpL7a accumulates in the nucleus, where ribosome biogenesis occurs. Mice immunized with TcRpL7a::his presented high levels of IgG1 and IgG2a antibodies and INF-g secreting cells as well. Ongoing experiments are being done to evaluate the capacity of TcRpL7a to generate protection in mice against parasite infection.