Biochemical assembly of the EBV B cell triggering complex.
(A) In-vitro assembly of the EBV gHgL/gp42/HLA-DQ2 triggering complex (red, indicated by arrow) using size exclusion chromatography (S200). The triggering complex elutes at 10.7 ml (Ve, elution volume) with an estimated apparent MW of 255 kDa (also see Table 1). This complex is formed from EBV gHgL/gp42 complex (brown) mixed with excess HLA-DQ2 (green). Excess HLA-DQ2 can be seen as a second individual peak in the red trace. EBV gHgL/gp42 complex (brown) is formed quantitatively from 1∶1 molar mixture of gHgL (blue) and gp42 (purple). (B) Thermodynamic cycle linking the two pathways to the formation of the triggering complex. The horizontal (top and bottom) reactions represent the binding of HLA to either free gp42 or to gHgL/gp42 complexes, respectively. Similarly, the vertical (left and right) reactions represent the binding of gHgL to either gp42 or gp42/HLA complexes.