Structure
SAgs are produced intracellularly by bacteria and are released upon infection as extracellular mature toxins.
The sequences of these toxins are relatively conserved among the different subgroups. More important than sequence homology, the 3D structure is very similar among different SAgs resulting in similar functional effects among different groups.
Crystal structures of the enterotoxins reveals that they are compact, ellipsoidal proteins sharing a characteristic two-domain folding pattern comprising an NH2-terminal β barrel globular domain known as the oligosaccharide / oligonucleotide fold, a long α-helix that diagonally spans the center of the molecule, and a COOH terminal globular domain.
The domains have binding regions for the Major Histocompatibility Complex Class II (MHC Class II) and the T cell receptor (TCR), respectively.
Read more about this topic: Superantigen
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