B-cell receptor
The B- cell receptor (English B cell receptor, BCR), is a transmembrane protein and receptor on B cells to which an antibody is bound. The BCR is a key component of the humoral immune response.
Properties
After specific binding of an antigen by the antibody on the BCR B cells are stimulated to be activated and thus cell division and cell differentiation into memory B cells and plasma B cells. The BCR has two functions, one for signal transduction and endocytosis and for initiating the antigen presentation of peptides to MHC -2. Defects in the BCR lead to an impairment of the production of antibodies and the signal transduction, which results in an immune deficiency, autoimmunity, or malignancy.
Construction
The B- cell receptor consists of a ligand-binding function ( as a result also from a Oligomerisierungsfunktion ) and a Signaltransduktionsfunktion. Ligand binding is performed by the bound antibody ( IgD, IgM, IgA or IgE) and leads to the functions of the oligomerization, opsonization, and complement activation of neutralization. Signal transduction via CD79 heterodimer A and B, the components A and B are connected via disulfide bonds. Co-receptor by binding of a protein complex of CD19, CD21 (synonym CR2) and CD81 ( TAPA -1 interchangeably ) signal transduction is increased by about a factor of 100. This can also be a complement activation lead to activation of the BCR. CD79 A and B are transmembrane proteins with ITAM motifs on the cytosolic side of intracellular signal transduction. Signal transduction via PLC γ and NFAT, on PI3K, via IKK, and NF-KB, as well as the ERK. The signal transduction is also influenced by non-coding RNAs. About the IKK and NF -kB PLC γ is CD79 and other proteins activated, then binds the PLC - γ c- SMAC and hydrolyzes PIP2 to IP3 and diacylglycerol, two secondary messengers.
Various mutations of the B- cell receptor involved in the pathogenesis of B-cell tumors. Perhaps this is due to long-term activation of the BCR, or to differences in the oligomerization.