Structure and Interactions of NCAM Ig1-2-3 Suggest a Novel Zipper Mechanism for Homophilic Adhesion

Abstract

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.

Immobilized Pool of NCAM180 in the Postsynaptic Membrane Is Homeostatically Replenished by the Flux of NCAM180 from Extrasynaptic Regions

“…The intracellular domain of NCAM directly interacts with the spectrin scaffold accumulating in synapses (25,35). The extracellular domain of NCAM binds to the extracellular domains of NCAM molecules on adjacent membranes, thereby mediating homophilic cell adhesion interactions (48). In the present study, we found that disruption of the association of NCAM180 with the cytoskeleton reduces its accumulation in the postsynaptic membrane.…”

Neural Cell Adhesion Molecule (N-CAM) Homophilic Binding Mediated by the Two N-terminal Ig Domains Is Influenced by Intramolecular Domain-Domain Interactions

“…A number of Ig3-specific reagents have been reported to inhibit cellcell aggregation including antibodies, recombinant proteins, and peptides, and it has been proposed that self-association of the Ig3 domains is central to N-CAM binding (15)(16)(17)(18). However, we and others (3,19) have been unable to demonstrate self-association of the isolated Ig3 domain in solution. To evaluate the contribution of Ig3 to N-CAM homophilic binding, we produced recombinant Fc fusion proteins corresponding to just the N-terminal domain, Ig1, the N-terminal two domains, Ig12, and the N-terminal three domains, Ig123 (Fig.…”

“…The crystal structures of dimeric Ig12 and Ig123 identified the intercalation of Phe 19 into a pocket on the surface of Ig2 as a prominent feature of the interaction (19,20). Here, we have employed this point mutation to probe the role of the Ig12 interaction in N-CAM-mediated bead aggregation.…”

“…To address this possibility, we deleted the membrane proximal FnIII domain from the N-CAM-Fc fusion protein (⌬Fn2, Fig. 1A), FnIII and Ig domains are similar in size (19,30), and compared the ability of ⌬Fn2 to mediate bead aggregation with that of the wild-type protein. In this assay the ⌬Fn2 was as effective as the entire extracellular region in mediating aggregation (Fig.…”

IL-1β-induced pro-apoptotic signalling is facilitated by NCAM/FGF receptor signalling and inhibited by the C3d ligand in the INS-1E rat beta cell line

“…Structural evidence suggests that NCAM molecules form cis dimers in the cell membrane and these cis dimers mediate trans interactions between cells via formation of two-dimensional zippers [12,13]. In neurons the extracellular part of NCAM has been shown to bind and mediate phosphorylation/activation of the fibroblast growth factor receptor (FGFR) [14,15].…”