Figure 8.

Modeling of IgE bound to FcεRI reveals that one of the Fabs predominately lies parallel to the membrane. Each sphere represents a possible position of the antigen binding site of the Fab. Cε4 is present, but obscured by Cε2 and 3. The modeled structure not only accounts for the observed restricted mobility of Fabs on IgE relative to IgG, but also suggests that two neighboring IgE-FcεRI complexes are pre-disposed for ready cross-linking either by self-association or through a bridging protein. For more details of modeling see Hunt et al. (2012).