Further characterization ofTrypanosoma cruzi GP57/51 as the major antigen expressed by differentiating epimastigotes

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Abstract
Study ofTrypanosoma cruzi metacyclogenesis under chemically defined conditions showed that the expression of a group of acidic polypeptides with a molecular weight of 45–50 kDa is markedly increased on adhesion of epimastigotes to the culture vessels. Immunochemical analysis revealed that these developmentally regulated polypeptides are structurally related to, and possibly homologous with, a majorT. cruzi antigen, namely, GP57/51, a glycoprotein that has recently been characterized as a cysteine proteinase. The differentiation of epimastigotes into metacyclic trypomastigotes is accompanied by a 2- to 5-fold reduction in the concentration of GP57/51 antigen as determined by radioimmunoassays using monoclonal antibodies. Two-dimensional polyacrylamide gel electrophoretic analysis of metabolically labelled parasites indicated that this antigen is synthesized as a precursor with a molecular weight of 60 kDa, which is then processed to a level of 45–50 kDa via the formation of at least one intermediate processing product. The observation that expression of GP57/51-related products increases during epimastigote differentiation suggests an improtant role for this proteinase during the life cycle ofT. cruzi.