SAG2A protein from Toxoplasma gondii interacts with both innate and adaptive immune compartments of infected hosts

Abstract

BackgroundToxoplasma gondii is an intracellular parasite that causes relevant clinical disease in humans and animals. Several studies have been performed in order to understand the interactions between proteins of the parasite and host cells. SAG2A is a 22 kDa protein that is mainly found in the surface of tachyzoites. In the present work, our aim was to correlate the predicted three-dimensional structure of this protein with the immune system of infected hosts.MethodsTo accomplish our goals, we performed in silico analysis of the amino acid sequence of SAG2A, correlating the predictions with in vitro stimulation of antigen presenting cells and serological assays.ResultsStructure modeling predicts that SAG2A protein possesses an unfolded C-terminal end, which varies its conformation within distinct strain types of T. gondii. This structure within the protein shelters a known B-cell immunodominant epitope, which presents low identity with its closest phyllogenetically related protein, an orthologue predicted in Neospora caninum. In agreement with the in silico observations, sera of known T. gondii infected mice and goats recognized recombinant SAG2A, whereas no serological cross-reactivity was observed with samples from N. caninum animals. Additionally, the C-terminal end of the protein was able to down-modulate pro-inflammatory responses of activated macrophages and dendritic cells.ConclusionsAltogether, we demonstrate herein that recombinant SAG2A protein from T. gondii is immunologically relevant in the host-parasite interface and may be targeted in therapeutic and diagnostic procedures designed against the infection.

A new Toxoplasma gondii chimeric antigen containing fragments of SAG2, GRA1, and ROP1 proteins—impact of immunodominant sequences size on its diagnostic usefulness

“…Selection of these antigens for the construction of chimeric protein was based on earlier results obtained in the immunoassays, which determined the reactivity of these proteins with specific anti- T. gondii antibodies. The SAG2 antigen, which is identified as an intrinsically unstructured protein, can interact with many cellular and surface molecules of infected host (Macedo et al 2013 ). In previous studies, the usefulness of the recombinant SAG2 antigen was shown to be effective in detecting specifically anti- T. gondii antibodies in sera especially from the acute, but also from the chronic phase of toxoplasmosis (Hiszczyńska-Sawicka et al 2005 ; Lau and Fong 2008 ; Li et al 2000 ; Parmley et al 1992 ).…”

Screening and identification of host proteins interacting with Toxoplasma gondii SAG2 by yeast two-hybrid assay

“…Protein modelling is a useful method to further investigate the interaction between two proteins. Junior et al [ 30 ] reported that T. gondii SAG2A strongly interacts with both infected host innate and adaptive immune compartments. From their predicted protein structure modeling, SAG2A possessed an unfolded C-terminal end, which correlates the features of intrinsically unstructured proteins (IUP).…”

“…From their predicted protein structure modeling, SAG2A possessed an unfolded C-terminal end, which correlates the features of intrinsically unstructured proteins (IUP). Since IUP was able to interact with different molecules within the cells, IUP was associated with a variety of neurodegenerative diseases and viral virulence elements [ 30 ].…”

Importance of serological cross-reactivity amongToxoplasma gondii, Hammondiaspp.,Neosporaspp.,Sarcocystisspp. andBesnoitia besnoiti

“…An ELISA based on immuno-affinity-purified native NcSRS2 showed no significant cross-reactions when tested with sera from cattle experimentally infected with a variety of protozoan parasites including also ten cattle infected with T. gondii (Schares et al 2000). In addition, the TgSAG2A molecule has been demonstrated to be specific to T. gondii , considering that no cross-reactivity has been shown with N. caninum when using recombinant protein or even mimotopes derived from this molecular marker, as characterized by A4D12 MAb (Bela et al 2008; Carvalho et al 2008; Cunha-Junior et al 2010; Santana et al 2012; Macedo et al 2013). …”