The neural cell adhesion molecule (NCAM) promotes axonal outgrowth, presumably through an interaction with the fibroblast growth factor receptor (FGFR). NCAM also has a little-understood ATPase activity. We here demonstrate for the first time a direct interaction between NCAM (fibronectin type III [F3] modules 1 and 2) and FGFR1 (Ig modules 2 and 3) by surface plasmon resonance (SPR) analysis. The structure of the NCAM F3 module 2 was determined by NMR and the module was shown by NMR to interact with the FGFR1 Ig module 3 and ATP. The NCAM sites binding to FGFR and ATP were found to overlap and ATP was shown by SPR to inhibit the NCAM-FGFR binding, indicating that ATP probably regulates the NCAM-FGFR interaction. Furthermore, we demonstrate that the NCAM module was able to induce activation (phosphorylation) of FGFR and to stimulate neurite outgrowth. In contrast, ATP inhibited neurite outgrowth induced by the module.

The insulin and insulin-like growth factor 1 receptors activate overlapping signalling pathways that are critical for growth, metabolism, survival and longevity. Their mechanism of ligand binding and activation displays complex allosteric properties, which no mathematical model has been able to account for. Modelling these receptors' binding and activation in terms of interactions between the molecular components is problematical due to many unknown biochemical and structural details. Moreover, substantial combinatorial complexity originating from multivalent ligand binding further complicates the problem. On the basis of the available structural and biochemical information, we develop a physically plausible model of the receptor binding and activation, which is based on the concept of a harmonic oscillator. Modelling a network of interactions among all possible receptor intermediaries arising in the context of the model (35, for the insulin receptor) accurately reproduces for the first time all the kinetic properties of the receptor, and provides unique and robust estimates of the kinetic parameters. The harmonic oscillator model may be adaptable for many other dimeric/dimerizing receptor tyrosine kinases, cytokine receptors and G-proteincoupled receptors where ligand crosslinking occurs.

The neural cell adhesion molecule, NCAM, mediates Ca(2+)-independent cell-cell and cell-substratum adhesion via homophilic (NCAM-NCAM) and heterophilic (NCAM-non-NCAM molecules) binding. NCAM plays a key role in neural development, regeneration, and synaptic plasticity, including learning and memory consolidation. The crystal structure of a fragment comprising the three N-terminal Ig modules of rat NCAM has been determined to 2.0 A resolution. Based on crystallographic data and biological experiments we present a novel model for NCAM homophilic binding. The Ig1 and Ig2 modules mediate dimerization of NCAM molecules situated on the same cell surface (cis interactions), whereas the Ig3 module mediates interactions between NCAM molecules expressed on the surface of opposing cells (trans interactions) through simultaneous binding to the Ig1 and Ig2 modules. This arrangement results in two perpendicular zippers forming a double zipper-like NCAM adhesion complex.

Human type 1 insulin-like growth factor receptor is a homodimeric receptor tyrosine kinase that signals into pathways directing normal cellular growth, differentiation and proliferation, with aberrant signalling implicated in cancer. Insulin-like growth factor binding is understood to relax conformational restraints within the homodimer, initiating transphosphorylation of the tyrosine kinase domains. However, no three-dimensional structures exist for the receptor ectodomain to inform atomic-level understanding of these events. Here, we present crystal structures of the ectodomain in apo form and in complex with insulin-like growth factor I, the latter obtained by crystal soaking. These structures not only provide a wealth of detail of the growth factor interaction with the receptor’s primary ligand-binding site but also indicate that ligand binding separates receptor domains by a mechanism of induced fit. Our findings are of importance to the design of agents targeting IGF-1R and its partner protein, the human insulin receptor.

The Neural Cell Adhesion Molecule (NCAM) plays a crucial role in development of the central nervous system regulating cell migration, differentiation and synaptogenesis. NCAM mediates cell-cell adhesion through homophilic NCAM binding, subsequently resulting in activation of the fibroblast growth factor receptor (FGFR). NCAM-mediated adhesion leads to activation of various intracellular signal transduction pathways, including the Ras-mitogen activated protein kinase (MAPK) and the phosphatidylinositol-3-kinase (PI3K)-Akt pathways. A synthetic peptide derived from the second fibronectin type III module of NCAM, the FGL peptide, binds to and induces phosphorylation of FGFR without prior homophilic NCAM binding. We here present evidence that this peptide is able to mimic NCAM heterophilic binding to the FGFR by inducing neuronal differentiation as reflected by neurite outgrowth through a direct interaction with FGFR in primary cultures of three different neuronal cell types all expressing FGFR subtype 1: dopaminergic, hippocampal and cerebellar granule neurons. Moreover, we show that the FGL peptide promotes neuronal survival upon induction of cell death in the same three cell types. The effects of the FGL peptide are shown to depend on activation of FGFR and the MAPK and PI3K intracellular signalling pathways, all three kinases being necessary for the effects of FGL on neurite outgrowth and neuronal survival. The neural cell adhesion molecule, NCAM, is a membraneassociated glycoprotein expressed on the surface of neurons and glial cells. NCAM plays a key role in morphogenesis of the nervous system, synaptic plasticity in relation to learning and memory consolidation, and regeneration of damaged neural tissue (Rønn et al. 1998).NCAM is a member of the immunoglobulin (Ig) superfamily and mediates cell)cell adhesion. It is involved in homophilic interactions (NCAM binding to NCAM) between opposing, NCAM-expressing cells and heterophilic binding between NCAM and a series of proteins including the fibroblast growth factor receptor (FGFR), the neuronal cell adhesion molecule L1 and different types of collagens and proteoglycans Crossin and Krushel 2000;Povlsen et al. 2003;Hinsby et al. 2004). Additionally, NCAM has recently been shown to bind glial cell Abbreviations used: Ab 25-35, Amyloid-b peptide; BDNF, brainderived neurotrophic factor; CGN, cerebellar granule neurons; Erk1/2, extracellular signal-regulated kinases 1 and 2; F3, fibronectin type III module; FAK, focal adhesion kinase; FGFR, fibroblast growth factor receptor; FGLd, FG loop peptide dendrimer; FGLm, FG loop peptide monomer; GDNF, glial cell line-derived neurotrophic factor; Ig, immunoglobulin; IGF-1, insulin-like growth factor 1; MAPK, Ras-mitogen activated protein kinase; NCAM, neural cell adhesion molecule; 6-OHDA, 6-hydroxydopamine; PI3K, phosphatidylinositol-3-kinase; PKC, protein kinase C; PLCc, phospholipase Cc.