One Lyn Molecule Is Sufficient to Initiate Phosphorylation of Aggregated High-Affinity IgE Receptors

In response to antigenic stimuli, the multi-subunit immune recognition receptors become aggregated and then phosphorylated on their cytoplasmic tyrosines. For the clonotypic receptors of B and T cells and for Fc receptors such as the high-affinity receptor for IgE (Fcε RI), a Src family kinase initiates this phosphorylation. We ask whether aggregation of the initiating kinase itself is required for signal transduction or whether, alternatively, a single associated kinase molecule can phosphorylate the receptors in an aggregate. We formulate the alternative molecular mechanisms mathematically and compare predictions with experimental findings on Fcε RI-bearing cells expressing varying amounts of the transfected Src family kinase Lyn. The data are consistent with the requirement of only a single Lyn molecule per Fcε RI aggregate to initiate signaling and are inconsistent with a mechanism requiring more than one Lyn molecule.