Figure 6-8
The BCR complex
•Ag binding chains – identical to secreted Ig, except for a hydrophobic transmembrane region and a short (3 aa) intracellular motif. (differential. splicing)
• Accessory chains – Igα and Igβ (necessary for transport to membrane, signal transduction, have single Ig fold domain, are disulfide-linked, and are non-covalently associated).
• Immunoreceptor tyrosine-based activation motifs (ITAMs) - Each contain a single ITAM sequence, consisting of 9-12 residues (used by other receptors in macs, NK cells, etc). Typical motif:
   Y X X L/I X6-9 Y X X L\I
Y=tyrosine, L=leucine, I= isoleucine, X=Any amino acid (spacing is important for “second level” kinases, Syk and Zap70)