Fig. 2.

Cartoon representation of an IGHV3-Fab domain with the Domain D of Staphylococcus aureus protein A (SpA). Schematic depiction of the BCR on a B cell (left) and the crystallographic structure of its human Fab fragment in association with SpA (in the circle). The heavy chain is shown in blue, the light chain is shown in red and the antigen-binding site with all CDRs is highlighted in purple. In addition, the amino acids which are necessary for the interaction of SpA (orange) with the Fab are depicted by spheres. Note that all but one amino acid are located in the framework region of the Fab. Neither the light chain nor the antigen-binding site contributes to SpA binding. Image adapted from the crystallographic structure published previously [78]. PDB: 1DEE