The transmembrane (TM) and juxtamembrane (JM) regions of the ErbB family receptor tyrosine kinases connect the extracellular ligand-binding domain to the intracellular kinase domain. Evidence for the role of these regions in the mechanism of receptor dimerization and activation is provided by TM-JM peptides corresponding to the Neu (or rat ErbB2) receptor. Solid-state NMR and fluorescence spectroscopy show that there are tight interactions of the JM sequence with negatively charged lipids, including phosphatidylinositol 4,5-bisphosphate, in TM-JM peptides corresponding to the wildtype receptor sequence. We observe a release of the JM sequence from the negatively charged membrane surface using peptides containing an activating V664E mutation within the TM domain or in peptides engineered to form TM helix dimers with Val664 in the interface. These results provide the basis of a mechanism for coupling ligand binding to kinase activation in the full-length receptor.EGF receptor | HER2 receptor | PIP 2 T he receptor tyrosine kinases (RTKs) are a large family of membrane receptors that control cell growth, differentiation, and migration. These receptors have a three-domain architecture consisting of an extracellular ligand-binding domain, a single transmembrane helix, and an intracellular kinase domain. Receptor activation is triggered by ligand-mediated dimerization of receptor monomers or the structural rearrangement of inactive, preformed dimers (1, 2). Detailed information about the mechanisms of activation and regulation of RTKs has come largely from crystal structures of their extracellular and intracellular domains in inactive and active conformations. The activation mechanisms of the ErbB subfamily of RTKs are of particular interest because mutations and deletions that result in constitutive receptor activity have been identified in a number of human tumors (3, 4).In the epidermal growth factor receptor (EGFR), a member of the ErbB subfamily, the structures of the extracellular domain with (5) and without (6) bound EGF revealed that the unliganded structure has a tethered conformation that undergoes a dramatic rearrangement upon ligand binding. On the intracellular side of the EGFR, crystal structures show that the activation loop associated with the active site in the kinase domain is in an open, active conformation before ligand binding (7) or locked in a Src tyrosine kinase/cyclin-dependent kinase-like inactive conformation (8). Activation is produced not via phosphorylation of the activation loop, as in other RTKs, but through the association of the intracellular kinase domains as an asymmetric dimer (8). An open question has involved how structural changes induced by ligand binding lead to the formation of an active, asymmetric dimer on the intracellular side of the receptor.The single transmembrane (TM) helix and associated juxtamembrane (JM) sequences bridge the extracellular and intracellular domains and require a membrane environment to adopt their native structure. In general, ligand binding to the e...