October 2007 QUIZ OF THE MONTH . . .
The high affinity, cell surface receptor for IgE (Fc epsilon R1) is a heterotetramer. Which one(s) of its units contain an ITAM (tyrosine -based activation motif)?
- Alpha-subunit.
- Beta-subunit.
- Only one of the two gamma subunits.
- Both of the gamma subunit chains.
Discussion
The Fc epsilon receptor 1 has an alpha-subunit which does not have a long intracellular component. It is the binding site for IgE. Signaling is done through the beta-subunit, and both disulfide linked gamma subunits. The beta and both gamma chains contain an ITAM which accounts for their ability to conduct intracellular signalling. ITAMs are typically 26 or 27 amino acid residues that transmit intracellular signalling because they contain docking sites for Syk kinase family members.References
1. Dombrowicz Z, et al. Anaphylaxis mediated through a humanized high affinity IgE receptor. J Immunol 1996; 157:1645-1651.
2. Helm B, et al. The mast cell binding site on human immunoglobulin E. Nature 1988; 331:180-183."
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