Similarities between the primary structures of two distinct major surface proteins of Toxoplasma gondii.
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 encoding a primary product of 385 amino acid residues. The deduced amino acid sequence contains a putative NH2-terminal signal sequence, as well as a glycosylphosphatidylinositol anchor attachment site. It is characterized by 12 cysteine residues whose distribution suggests a tandem duplication of a single ancestral motif containing 6 cysteine residues. Although no DNA sequence analogies were found, comparative amino acid sequence analysis detected a resemblance to SAG1, which is the major surface antigen specifically expressed by the proliferative tachyzoite stage. Despite a low degree of identity between the two amino acid sequences (24%), the conservative distribution of the cysteine and tryptophan residues, as well as of repeated motifs, together with oligopeptide identities suggest similar folding and possibly similar function for both proteins.
Cesbron-Delauw
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MF
Centre d'Immunologie et de Biologie Parasitaire, Unité mixte INSERM U167, CNRS 624, Institut Pasteur, Lille, France.
Tomavo
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S
Beauchamps
P
P
Fourmaux
M P
MP
Camus
D
D
Capron
A
A
Dubremetz
J F
JF
D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D017125:Genes, Protozoan / Q000235:genetics*; D008562:Membrane Glycoproteins / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014122:Toxoplasma / Q000235:genetics*
D000953:Antigens, Protozoan; D018076:DNA, Complementary; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D015800:Protozoan Proteins; C047168:SAG1 antigen, Toxoplasma; C087692:SAG3 protein, Toxoplasma gondii