Abstract
Binding of antigen to the B cell receptor (BCR) induces conformational changes in BCR's cytoplasmic domains that are concomitant with phosphorylation of the immunoreceptor tyrosine-based activation motifs (ITAMs). Recently, reversible folding of the CD3ε and ξ chain ITAMs into the plasma membrane has been suggested to regulate T cell receptor signaling. Here we show that the Igα and Igβ cytoplasmic domains of the BCR do not associate with plasma membrane in resting B cells. However, antigen binding and ITAM phosphorylation specifically increased membrane proximity of Igα, but not Igβ. Thus, BCR activation is accompanied by asymmetric conformational changes, possibly promoting the binding of Igα and Igβ to differently localized signaling complexes.
Highlights
The B cell receptor (BCR) provides signals for the development, activation and differentiation of B lymphocytes
To investigate the relationship of the cytoplasmic domains of Iga and Igb to the plasma membrane in unstimulated cells, we used Florescence resonance energy transfer (FRET) to measure proximity between cyan fluorescent protein (CFP) attached to the C-termini of Iga and Igb constructs, and the lipophilic dye octadecyl rhodamine B chloride (R18), which incorporates into the plasma membrane
To set up FRET experiments, we transfected HEK293T cells with constructs of Iga and Igb, together with IgM heavy chain and Igl light chain, which resulted in expression of the BCR constructs at the plasma membrane
Summary
The B cell receptor (BCR) provides signals for the development, activation and differentiation of B lymphocytes. We used FRET in live B cells to measure the proximity of BCR cytoplasmic domains to the plasma membrane in the resting state and upon antigen binding.
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