Molecular Characterization of a Novel Family of Trypanosoma cruzi Surface Membrane Proteins (TcSMP) Involved in Mammalian Host Cell Invasion

Abstract

BackgroundThe surface coat of Trypanosoma cruzi is predominantly composed of glycosylphosphatidylinositol-anchored proteins, which have been extensively characterized. However, very little is known about less abundant surface proteins and their role in host-parasite interactions.Methodology/ Principal FindingsHere, we described a novel family of T. cruzi surface membrane proteins (TcSMP), which are conserved among different T. cruzi lineages and have orthologs in other Trypanosoma species. TcSMP genes are densely clustered within the genome, suggesting that they could have originated by tandem gene duplication. Several lines of evidence indicate that TcSMP is a membrane-spanning protein located at the cellular surface and is released into the extracellular milieu. TcSMP exhibited the key elements typical of surface proteins (N-terminal signal peptide or signal anchor) and a C-terminal hydrophobic sequence predicted to be a trans-membrane domain. Immunofluorescence of live parasites showed that anti-TcSMP antibodies clearly labeled the surface of all T. cruzi developmental forms. TcSMP peptides previously found in a membrane-enriched fraction were identified by proteomic analysis in membrane vesicles as well as in soluble forms in the T. cruzi secretome. TcSMP proteins were also located intracellularly likely associated with membrane-bound structures. We demonstrated that TcSMP proteins were capable of inhibiting metacyclic trypomastigote entry into host cells. TcSMP bound to mammalian cells and triggered Ca2+ signaling and lysosome exocytosis, events that are required for parasitophorous vacuole biogenesis. The effects of TcSMP were of lower magnitude compared to gp82, the major adhesion protein of metacyclic trypomastigotes, suggesting that TcSMP may play an auxiliary role in host cell invasion.Conclusion/SignificanceWe hypothesized that the productive interaction of T. cruzi with host cells that effectively results in internalization may depend on diverse adhesion molecules. In the metacyclic forms, the signaling induced by TcSMP may be additive to that triggered by the major surface molecule gp82, further increasing the host cell responses required for infection.

Autophagy: A necessary process during the Trypanosoma cruzi life-cycle

“…The T. cruzi entry process was classically divided into two specific steps (Figure 1, points 1 and 2): the adhesion process, related to the binding of T. cruzi antigens to host cell receptors which trigger cell signaling events [6,7]; and the internalization process that describes the mechanism that culminates in the formation of the T. cruzi parasitophorous vacuole (TcPV). Adhesion of trypomastigotes is driven by a repertoire of molecules present at the parasite surface or secreted during the infection process which bind to the specific receptors in the host cells [6,8,9]. Despite the advances made towards identification of the receptor molecule responsible for the adhesion of parasites, no single main host receptor candidate has been identified yet.…”

Characterization and Diagnostic Application of Trypanosoma cruzi Trypomastigote Excreted-Secreted Antigens Shed in Extracellular Vesicles Released from Infected Mammalian Cells

“…Interestingly, treatment of mice with EVs shed by axenic trypomastigotes caused a downmodulation of the host immune response that was associated with higher parasitemia and an exacerbated inflammatory response that resulted in increased mortality following infection (26,35). The T. cruzi small membrane proteins (TcSMP) family of proteins or phosphatases detected on T. cruzi EVs has been shown to trigger Ca 2ϩ signaling and lysosome mobilization/exocytosis, events that promote formation of parasitophorous vacuoles and parasite invasion (36,37). A similar modulation of macrophage responses was observed following exposure to purified Leishmania exosomes, a strategy that enhances intracellular parasite survival (38,39).…”

Role of Proteomics in the Study of Trypanosoma cruzi Biology

“…TcSMPs could bind to mammalian cells and trigger Ca 2+ signaling and lysosome exocytosis. This evidence strongly suggests the involvement of these proteins in parasite invasion [34].…”