Detailed illustration of the Ca2⁺-initiation complex of T cells. The central unit of this complex is the TRAP LAT, which recruits the Gads/SLP-76 complex and PLCγ1 to the lipid rafts after phosphorylation by ZAP-70. The tyrosine kinase Itk binds with its SH2 domain to phosphorylated SLP-76 and is thus also brought into the vicinity of PLCγ1. ZAP-70 and Itk now phosphorylate and activate PCLγ1, which, in turn, hydrolyzes PIP₂ and generates the second-messenger molecules DAG and PIP₃. Note that Gads and SLP-76 constitutively interact with each other via the SH3 domain of Gads and a proline-rich region in SLP-76.