High Diversity in Mucin Genes and Mucin Molecules in Trypanosoma cruzi

Javier M Di Noia,Guido D Pollevick,Marcia T Xavier,José O Previato,Lucia Mendoça-Previato,Daniel O Sánchez,Albertoc C Frasch

doi:10.1074/jbc.271.50.32078

Abstract

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.

Highlights

Mucins are highly O-glycosylated molecules composed of up to 80% of carbohydrate attached to Thr and Ser residues of the
In this paper we present evidence that the products encoded by the putative mucin gene family are the core proteins of T. cruzi mucin-type glycoproteins, and that diversity among these genes and glycoproteins is greater than previously thought
The MUC-like Gene Family of T. cruzi Encodes Mucin-type Glycoproteins—In a previous work we have described a putative mucin gene family, which we called MUC-like genes in analogy with MUC genes from mucins in vertebrates [17]

Summary

Introduction

Mucins are highly O-glycosylated molecules composed of up to 80% of carbohydrate attached to Thr and Ser residues of the. The main SA acceptors in epimastigotes (insect vector replicative form of T. cruzi) and metacyclic forms (insect-derived infective stage) are mucin-type, glycophosphatidylinositol (GPI)anchored, glycoproteins migrating in the 35–50-kDa range depending on the parasite strain [10, 12, 13] Mucins of both developmental stages have different biological properties even though they are recognized by the same mAbs [12]. In the trypomastigote form (the cell-derived infective stage in the mammalian host), glycoproteins sharing the stage-specific epitope Ssp-3, which is dependent on parasite sialylation, are the main SA acceptors [8, 11] They were shown to be of mucin-type and GPI-anchored to the parasite membrane [5]. We have recently identified in T. cruzi genes whose overall structure resembles those coding for mammalian mucins

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Conclusion