High diversity in mucin genes and mucin molecules in Trypanosoma cruzi

Mucins are highly O-glycosylated molecules which in mammalian cells accomplish essential functions, like cytoprotection and cell-cell interactions. In the protozoan parasite Trypanosoma cruzi, mucin-related glycoproteins have been shown to play a relevant role in the interaction with and invasion of host cells. We have previously reported a family of mucin-like genes in T. cruzi whose overall structure resembled that of mammalian mucin genes. We have now analyzed the relationship between these genes and mucin proteins. A monoclonal antibody specific for a mucin sugar epitope and a polyclonal serum directed to peptide epitopes in a MUC gene-encoded recombinant protein, detected identical bands in three out of seven strains of T. cruzi. Immunoprecipitation experiments confirmed these results. When expressed in eukaryotic cells, the MUC gene product is post-translationally modified, most likely, through extensive O-glycosylation. Gene sequencing showed that the central domains encoding the repeated sequences with the consensus T8KP2, varies in number from 1 to 10, and the number of Thr residues in each repeat could be 7, 8, or 10. A run of 16 to 18 Thr residues was present in some, but not all, MUC gene-derived sequences. Direct compositional analysis of mucin core proteins showed that Thr residues are much more frequent than Ser residues. The same fact occurs in MUC gene-derived protein sequences. Molecular mass determinations of the 35-kDa glycoproteins further extend the heterogeneity of the family to the natural mucin molecules. Difficulties in assigning each of the several MUC genes identified to a mucin product arise from the high diversity and partial sequence conservation of the members of this family.