Comparative Analysis of the Secretome and Interactome of Trypanosoma cruzi and Trypanosoma rangeli Reveals Species Specific Immune Response Modulating Proteins

Abstract

Chagas disease, a zoonosis caused by the flagellate protozoan Trypanosoma cruzi, is a chronic and systemic parasitic infection that affects ~5-7 million people worldwide, mainly in Latin America. Chagas disease is an emerging public health problem due to the lack of vaccines and effective treatments. According to recent studies, several T. cruzi secreted proteins interact with the human host during cell invasion. Moreover, some comparative studies with T. rangeli, which is non-pathogenic in humans, have been performed to identify proteins directly involved in the pathogenesis of the disease. In this study, we present an integrated analysis of canonical putative secreted proteins (PSPs) from both species. Additionally, we propose an interactome with human host and gene family clusters, and a phylogenetic inference of a selected protein. In total, we identified 322 exclusively PSPs in T. cruzi and 202 in T. rangeli. Among the PSPs identified in T. cruzi, we found several trans-sialidases, mucins, MASPs, proteins with phospholipase 2 domains (PLA2-like), and proteins with Hsp70 domains (Hsp70-like) which have been previously characterized and demonstrated to be related to T. cruzi virulence. PSPs found in T. rangeli were related to protozoan metabolism, specifically carboxylases and phosphatases. Furthermore, we also identified PSPs that may interact with the human immune system, including heat shock and MASP proteins, but in a lower number compared to T. cruzi. Interestingly, we describe a hypothetical hybrid interactome of PSPs which reveals that T. cruzi secreted molecules may be down-regulating IL-17 whilst T. rangeli may enhance the production of IL-15. These results will pave the way for a better understanding of the pathophysiology of Chagas disease and may ultimately lead to the identification of molecular targets, such as key PSPs, that could be used to minimize the health outcomes of Chagas disease by modulating the immune response triggered by T. cruzi infection.

Keywords: IL15; IL17; Trypanosoma cruzi; Trypanosoma rangeli; interactome; secretome.

Figure 1

Identification of the potentially secreted proteins (PSPs) of T. cruzi and T. rangeli. (A) Trypanosome species analyzed. Number of total protein sequences, amount of protein sequences with signal peptide [SIGNAL PEPTIDE (+)] and without transmembrane domains [TRANSMEMBRANE (-)]. Percentage of PSPs identified from the genome of each species; (B) Biological processes of the T. cruzi PSPs found by the Blast2Go program. The numbers given in parentheses show the amount of proteins related to a given biological function; (C) Biological processes of the T. rangeli PSPs found by the Blast2Go program. The numbers given in parentheses show the amount of proteins related to a given biological function; (D) Quantitative analysis by OrthoMCL. Amount of grouped proteins found in each organism and in both species.

Figure 2

Patatin phospholipase domain has not been acquired by horizontal transfer (HGT). (A) Neighbor-joining (NJ) phylogenetic analysis of PLA2 patatin protein motif sequences from several species. The phylogenetic tree was constructed using 4,354 amino acid sequences aligned by Muscle with NJ algorithm, provided with Seaview. The branch length is proportional to amino acid differences. (a) NJ phylogenetic edited tree showing three distinct Trypanosoma species branches. SYLVIO strain EKG05184 (used as the query in the BLAST search) is highlighted, other species are included in collapsed branches. (b) Global NJ phylogenetic tree with all 4,354 species; three Trypanosoma branches are highlighted. There were no distant species inserted in Trypanosoma branches indicating HGT. (B) Bayesian tree constructed based on a set with 78 PLA2 patatin protein motif sequences. Node labels represent the posterior probabilities values. There were no distant species in Trypanosoma branches indicating HGT.

Figure 3

Hypothetical hybrid interactome revealed proteins potentially involved in host immune modulation. Gene and functional interaction networks for potential T. cruzi (A) and T. rangeli (B) PSPs (red nodes) identified by screening for orthologous genes in human protein databases. Molecules are represented as nodes (shaded gray), and the biological relationship between two nodes is represented as an edge (line). A line denotes binding of proteins, whereas a line with an arrow denotes that one protein acts on another. A dotted line denotes an indirect relationship. Each node shape represents one type of molecule, as described in the figure legend. Molecules in orange represent activation and those in blue represent inhibition. Colorless molecules indicate no prediction of interaction.