Molecular Characterization of Serine-, Alanine-, and Proline-Rich Proteins of Trypanosoma cruzi and Their Possible Role in Host Cell Infection

• Published in: Infection and Immunity Vol. 74; no. 3; pp. 1537 - 1546
• Main Authors: Baida, Renata C. P, Santos, Márcia R. M, Carmo, Mirian S, Yoshida, Nobuko, Ferreira, Danielle, Ferreira, Alice Teixeira, El Sayed, Najib M, Andersson, Bjorn, Silveira, José Franco da
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01-03-2006
• Subjects: Alanine - chemistry; Amino Acid Sequence; Animals; Biological and medical sciences; Calcium - analysis; Calcium - metabolism; Cell Adhesion Molecules - physiology; Fundamental and applied biological sciences. Psychology; Fungal and Parasitic Infections; Genome, Protozoan; HeLa Cells; Humans; Medicin och hälsovetenskap; Microbiology; Molecular Sequence Data; Peptides - genetics; Peptides - physiology; Proline; Proline-Rich Protein Domains; Protozoan Proteins - chemistry; Protozoan Proteins - genetics; Protozoan Proteins - physiology; Serine - chemistry; Trypanosoma cruzi; Trypanosoma cruzi - chemistry; Trypanosoma cruzi - genetics; Kinetoplastida; Protozoa; Alanine; Microbiology; Serine; Proline; Immunity; Protein; Trypanosoma cruzi
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.74.3.1537-1546.2006

We previously reported the isolation of a novel protein gene family, termed SAP (serine-, alanine-, and proline-rich protein), from Trypanosoma cruzi. Aided by the availability of the completed genome sequence of T. cruzi, we have now identified 39 full-length sequences of SAP, six pseudogenes and four partial genes. SAPs share a central domain of about 55 amino acids and can be divided into four groups based on their amino (N)- and carboxy (C)-terminal sequences. Some SAPs have conserved N- and C-terminal domains encoding a signal peptide and a glycosylphosphatidylinositol anchor addition site, respectively. Analysis of the expression of SAPs in metacyclic trypomastigotes by two-dimensional electrophoresis and immunoblotting revealed that they are likely to be posttranslationally modified in vivo. We have also demonstrated that some SAPs are shed into the extracellular medium. The recombinant SAP exhibited an adhesive capacity toward mammalian cells, where binding was dose dependent and saturable, indicating a possible ligand-receptor interaction. SAP triggered the host cell Ca²⁺ response required for parasite internalization. A cell invasion assay performed in the presence of SAP showed inhibition of internalization of the metacyclic forms of the CL strain. Taken together, these results show that SAP is involved in the invasion of mammalian cells by metacyclic trypomastigotes, and they confirm the hypothesis that infective trypomastigotes exploit an arsenal of surface glycoproteins and shed proteins to induce signaling events required for their internalization.