The SAG2 antigen of Toxoplasma gondii and the 31-kDa surface antigen of Sarcocystis muris share similar sequence features

Abstract

In the search for similar cysteine distribution patterns among surface antigens of members of the phylum of Apicomplexa, we found a resemblance between TgSAG2, a 22-kDa surface antigen of Toxoplasma gondii, and the C-terminal half of a 31-kDa surface antigen of Sarcocystis muris, SmSAG1. The overall degree of similarity is low, corresponding to 28% of identity in the 146 amino acids aligned. However, the conservative spacing between the cysteine residues suggest that this similarity might have functional implications. The described amino acid similarity provides a new clue to the molecular relationship between two closely related coccidian parasites.