Trypanosoma cruzi: monoclonal antibody to cytoskeleton recognizes giant proteins of the flagellar attachment zone.

Cytoskeletal preparations of Trypanosoma cruzi trypomastigotes and epimastigotes contain a protein recognized by a monoclonal antibody (2G4) which is connected to the flagellar attachment zone of both stages of the parasite. Western blot analysis revealed that the antibody was able to recognize protein bands of molecular masses higher than 700 kDa up to 2500 kDa. These giant proteins do not seem to share sequences with beta-connectin since an anti-beta-connectin antibody did not recognize the T. cruzi proteins nor did the 2G4 monoclonal antibody recognize authentic beta-connectin. Immunofluorescence and immunogold electron microscopy provided evidence that this protein is located inside the cell body of the parasite, closely related to a corset of four microtubules known as subpellicular microtubule quartet. Immunogold labeling shows that the protein accompanies the flagellar attachment zone as long as the flagellum adheres to the cell body. It is proposed that these microtubule-associated proteins recognized by the 2G4 monoclonal antibody exist only in trypanosomatid forms having a junctional complex between the flagellum and the cell body and may act as transmembrane elements connecting the subpellicular microtubular quartet with the flagellum at the desmosome region.