Fig. 1.

The ‘conformation-induced oligomerization’ model for the initiation of BCR signaling. From left to right: In the absence of antigen the BCR (blue H chain, cyan L chains, green IgαIgβ) is freely diffusing in the B cell membrane in a conformation that is not permissive for oligomerization. Binding to monovalent antigen on an APC surface reveals an oligomerization face in the Cμ3 ectodomain of the BCR. The antigen bound BCR is still freely diffusing but stops when it encounters another antigen bound BCR and oligomerizes. The BCR oligomer perturbs the local lipid environment resulting in the coalescence of saturated lipids (in purple) around the oligomer resulting in the simultaneous recruitment of the membrane tethered Lyn (yellow color) and the ‘opening’ of the BCR cytoplasmic domains. Lyn’s phosphorylation of the BCR ITAMs triggers the signaling pathways.