Superantigens (SAGs) are a class of immunostimulatory proteins of bacterial or viral origin that activate T cells by binding to the Vβ domain of the T cell antigen receptor (TCR). The three-dimensional structure of the complex between a TCR β chain (mouse Vβ8.2) and the SAG staphylococcal enterotoxin B (SEB) at 2.4 A resolution reveals why SEB recognizes only certain Vβ families, as well as why only certain SAGs bind mouse Vβ8.2. Models of the TCR-SEB-peptide/MHC class II complex indicate that Vα interacts with the MHC β chain in the TCR-SAG-MHC complex. The extent of the interaction is variable and is largely determined by the geometry of Vα/Vβ domain association. This variability can account for the preferential expression of certain Vα regions among T cells reactive with SEB.
Hongmin, L., Llera, A., Tsuchiya, D., Leder, L., Ysern, X., Schlievert, P. M., … Mariuzza, R. A. (1998). Three-dimensional structure of the complex between a T cell receptor β chain and the superantigen staphylococcal enterotoxin B. Immunity, 9(6), 807–816. https://doi.org/10.1016/S1074-7613(00)80646-9