Local changes in lipid environment of TCR microclusters regulate membrane binding by the CD3ε cytoplasmic domain

The CD3 epsilon and xi cytoplasmic domains of the T cell receptor bind to the inner leaflet of the plasma membrane (PM), and a previous nuclear magnetic resonance structure showed that both tyrosines of the CD3 epsilon immunoreceptor tyrosine-based activation motif partition into the bilayer. Electrostatic interactions between acidic phospholipids and clusters of basic CD3 epsilon residues were previously shown to be essential for CD3 epsilon and xi membrane binding. Phosphatidylserine (PS) is the most abundant negatively charged lipid on the inner leaflet of the PM and makes a major contribution to membrane binding by the CD3 epsilon cytoplasmic domain. Here, we show that TCR triggering by peptide-MHC complexes induces dissociation of the CD3 epsilon cytoplasmic domain from the plasma membrane. Release of the CD3 epsilon cytoplasmic domain from the membrane is accompanied by a substantial focal reduction in negative charge and available PS in TCR microclusters. These changes in the lipid composition of TCR microclusters even occur when TCR signaling is blocked with a Src kinase inhibitor. Local changes in the lipid composition of TCR microclusters thus render the CD3 epsilon cytoplasmic domain accessible during early stages of T cell activation.