Figure 3

Orthologue SAG2A from Neospora caninum presents distinct conformation of the C-terminal end and does not share immunodominant B cell-epitope with T. gondii. (A) The consensus tree of SAG2 and SAG1 protein sequences demonstrates higher proximity of SAG2A with its predicted orthologue from Neospora caninum (NcSAG2A). (B) Modeling of NcSAG2A suggests that overall structure of the orthologues is similar, although its loop is composed with beta-sheets instead of the largely disordered structure of T. gondii’s protein. Additionally, the B cell-epitope sequence found in SAG2A (purple highlight) is not present in its orthologue. (C) Sequence alignments produced by ClustalW with SAG2A orthologues demonstrate the percentage of identity and similarity between these proteins, found to be low in the loop sequence and practically nonexistent in the B cell-epitope region of the amino acid sequence. The unfolded C-terminal end of T. gondii SAG2A is highlighted in blue, which includes an immunodominant epitope NDGSSA highlighted in red. (D) Reactivity of IgG antibodies from naïve mice and mice experimentally infected with N. caninum or T. gondii against recombinant SAG2A protein of T. gondii. Sera reactivity was expressed as ELISA index (EI). (E) Recognition profile of recombinant SAG2A by serum samples from experimentally infected mice and naturally infected goats with T. gondii and N. caninum in Western Blot.