We have determined the 3.2 A X-ray crystal structure of the extracellular domain of the human epidermal growth factor receptor 2 (ErbB2 or HER2) in a complex with the antigen binding fragment of pertuzumab, an anti-ErbB2 monoclonal antibody also known as 2C4 or Omnitarg. Pertuzumab binds to ErbB2 near the center of domain II, sterically blocking a binding pocket necessary for receptor dimerization and signaling. The ErbB2-pertuzumab structure, combined with earlier mutagenesis data, defines the pertuzumab residues essential for ErbB2 interaction. To analyze the ErbB2 side of the interface, we have mutated a number of residues contacting pertuzumab and examined the effects of these mutations on pertuzumab binding and ErbB2-ErbB3 heterodimerization. We have also shown that conserved residues previously shown to be necessary for EGF receptor homodimerization may be dispensible for ErbB2-ErbB3 heterodimerization.

The proin¯ammatory cytokine interleukin 17 is the founding member of a family of secreted proteins that elicit potent cellular responses. We report a novel human IL-17 homolog, IL-17F, and show that it is expressed by activated T cells, can stimulate production of other cytokines such as IL-6, IL-8 and granulocyte colony-stimulating factor, and can regulate cartilage matrix turnover. Unexpectedly, the crystal structure of IL-17F reveals that IL-17 family members adopt a monomer fold typical of cystine knot growth factors, despite lacking the disul®de responsible for de®ning the canonical`knot' structure. IL-17F dimerizes in a parallel manner like neurotrophins, and features an unusually large cavity on its surface. Remarkably, this cavity is located in precisely the same position where nerve growth factor binds its high af®nity receptor, TrkA, suggesting further parallels between IL-17s and neurotrophins with respect to receptor recognition.

Vascular endothelial growth factor (VEGF) is a homodimeric hormone that induces proliferation of endothelial cells through binding to the kinase domain receptor and the Fms-like tyrosine kinase receptor (Flt-1), the extracellular portions of which consist of seven immunoglobulin domains. We show that the second and third domains of Flt-1 are necessary and sufficient for binding VEGF with near-native affinity, and that domain 2 alone binds only 60-fold less tightly than wild-type. The crystal structure of the complex between VEGF and the second domain of Flt-1 shows domain 2 in a predominantly hydrophobic interaction with the "poles" of the VEGF dimer. Based on this structure and on mutational data, we present a model of VEGF bound to the first four domains of Flt-1.

Vascular endothelial growth factor (VEGF) is a homodimeric member of the cystine knot family of growth factors, with limited sequence homology to platelet-derived growth factor (PDGF) and transforming growth factor ␤2 (TGF-␤). We have determined its crystal structure at a resolution of 2.5 Å, and identified its kinase domain receptor (KDR) binding site using mutational analysis. Overall, the VEGF monomer resembles that of PDGF, but its N-terminal segment is helical rather than extended. The dimerization mode of VEGF is similar to that of PDGF and very different from that of TGF-␤. Mutational analysis of VEGF reveals that symmetrical binding sites for KDR are located at each pole of the VEGF homodimer. Each site contains two functional ''hot spots'' composed of binding determinants presented across the subunit interface. The two most important determinants are located within the largest hot spot on a short, three-stranded sheet that is conserved in PDGF and TGF-␤. Functional analysis of the binding epitopes for two receptor-blocking antibodies reveal different binding determinants near each of the KDR binding hot spots.

Nerve growth factor (NGF) is involved in a variety of processes involving signalling, such as cell differentiation and survival, growth cessation and apoptosis of neurons. These events are mediated by NGF as a result of binding to its two cell-surface receptors, TrkA and p75. TrkA is a receptor with tyrosine kinase activity that forms a high-affinity binding site for NGF. Of the five domains comprising its extracellular portion, the immunoglobulin-like domain proximal to the membrane (TrkA-d5 domain) is necessary and sufficient for NGF binding. Here we present the crystal structure of human NGF in complex with human TrkA-d5 at 2.2 A resolution. The ligand-receptor interface consists of two patches of similar size. One patch involves the central beta-sheet that forms the core of the homodimeric NGF molecule and the loops at the carboxy-terminal pole of TrkA-d5. The second patch comprises the amino-terminal residues of NGF, which adopt a helical conformation upon complex formation, packing against the 'ABED' sheet of TrkA-d5. The structure is consistent with results from mutagenesis experiments for all neurotrophins, and indicates that the first patch may constitute a conserved binding motif for all family members, whereas the second patch is specific for the interaction between NGF and TrkA.