The mechanisms by which signals are transmitted across the plasma membrane to regulate signaling are largely unknown for receptors with single-pass transmembrane domains such as the epidermal growth factor receptor (EGFR). A crystal structure of the extracellular domain of EGFR dimerized by epidermal growth factor (EGF) reveals the extended, rod-like domain IV and a small, hydrophobic domain IV interface compatible with flexibility. The crystal structure and disulfide cross-linking suggest that the 7-residue linker between the extracellular and transmembrane domains is flexible. Disulfide cross-linking of the transmembrane domain shows that EGF stimulates only moderate association in the first two ␣-helical turns, in contrast to association throughout the membrane over five ␣-helical turns in glycophorin A and integrin. Furthermore, systematic mutagenesis to leucine and phenylalanine suggests that no specific transmembrane interfaces are required for EGFR kinase activation. These results suggest that linkage between ligand-induced dimerization and tyrosine kinase activation is much looser than was previously envisioned.Fundamental to cellular physiology is the ability to transmit extracellular signals across the cell membrane to trigger intracellular responses. Although the extracellular and intracellular portions of cell surface receptors are responsible for detecting ligands and initiating signal cascades, respectively, transmembrane (TM) domains are thought to play critical roles by specifically associating and propagating signals across the phospholipid bilayer. However, the mechanisms by which single-pass TM domains associate and conduct signals are poorly understood.The epidermal growth factor receptor (EGFR) is the prototypical type I TM receptor tyrosine kinase. EGFR and related members of the ErbB family-ErbB2, ErbB3, and ErbB4-contain a glycosylated extracellular ligand binding domain; a singlepass TM domain; and intracellular juxtamembrane, tyrosine kinase, and autophosphorylation domains. The extracellular domain of EGFR binds polypeptide growth factor ligands, such as epidermal growth factor (EGF), to stimulate an array of intracellular signaling cascades that regulate normal and oncogenic cellular growth and proliferation (3,17,36). In one model of growth factor-dependent EGFR activation, ligand binding promotes receptor dimerization and activation of intracellular protein tyrosine kinase activity (35); other models suggest that receptors are predimerized on the cell surface and ligand binding alters the equilibrium between inactive and active dimeric (or higher-order oligomeric) configurations (9, 29).Structural mechanisms of growth factor-mediated receptor dimerization and allosteric kinase domain activation have been proposed from recent crystal structures of isolated extracellular ligand binding domains (7) and intracellular tyrosine kinase domains (37). The orientation between the four extracellular domains is dramatically altered upon ligand binding, which frees interfaces that are masked in ...

In the present study, we re-annotated von Willebrand factor (VWF), assigned its entire sequence to specific modules, and related these modules to structure using electron microscopy (

Crystals soaked with RGD peptides reveal six intermediate conformational states between the closed and higher affinity, fully open state of the integrin αIIbβ3 headpiece.

Structures of intact receptors with single-pass transmembrane (TM) domains are essential to understand how extracellular and cytoplasmic domains regulate association and signaling through TM domains. A chemical and computational method to determine structures of the membrane regions of such receptors on the cell surface is developed here and validated with glycophorin. An integrin heterodimer structure reveals association over most of the lengths of the α and β TM domains, and that the principles governing association of hetero and homo TM dimers differ. A turn at the Gly of the juxtamembrane (JM) GFFKR motif caps the α TM helix, and brings the two Phe of GFFKR into the α/β interface. A JM Lys residue in β also has an important role in the interface. The structure is incompatible with previous NMR JM/cytoplasmic complex structures, and together with NMR structures of isolated α and β TM domains, shows how TM association/dissociation regulates integrin signaling. A joint ectodomain and membrane structure shows that substantial flexibility between the extracellular and TM domains is compatible with TM signaling.