Similarities between the primary structures of two distinct major surface proteins of Toxoplasma gondii

摘要: Toxoplasma gondii possesses a 43-kDa surface protein (SAG3) that is expressed by all invasive stages. We have cloned and sequenced cDNAs encoding SAG3, with the longest one primary product of 385 amino acid residues. The deduced sequence contains putative NH2-terminal signal sequence, as well glycosylphosphatidylinositol anchor attachment site. It characterized 12 cysteine residues whose distribution suggests tandem duplication single ancestral motif containing 6 Although no DNA analogies were found, comparative analysis detected resemblance to SAG1, which major antigen specifically proliferative tachyzoite stage. Despite low degree identity between two sequences (24%), conservative tryptophan residues, repeated motifs, together oligopeptide identities suggest similar folding possibly function for both proteins.