Crystal Structure of the V Domain of Human Nectin-like Molecule-1/Syncam3/Tsll1/Igsf4b, a Neural Tissue-specific Immunoglobulin-like Cell-Cell Adhesion Molecule

Abstract

Nectins are Ca2؉ -independent immunoglobulin (Ig) superfamily proteins that participate in the organization of epithelial and endothelial junctions. Nectins have three Ig-like domains in the extracellular region, and the first one is essential in cell-cell adhesion and plays a central role in the interaction with the envelope glycoprotein D of several viruses. Five Nectin-like molecules (Necl-1 through -5) with similar domain structures to those of Nectins have been identified. Necl-1 is specifically expressed in neural tissue, has Ca 2؉ -independent homophilic and heterophilic cell-cell adhesion activity, and plays an important role in the formation of synapses, axon bundles, and myelinated axons. Here we report the first crystal structure of its N-terminal Ig-like V domain at 2.4 Å , providing insight into trans-cellular recognition mediated by Necl-1. The protein crystallized as a dimer, and the dimeric form was confirmed by size-exclusion chromatography and chemical cross-linking experiments, indicating this V domain is sufficient for homophilic interaction. Mutagenesis work demonstrated that Phe 82 is a key residue for the adhesion activity of Necl-1. A model for homophilic adhesion of Necl-1 at synapses is proposed based on its structure and previous studies.The cell-cell adhesion systems play important roles in neuronal cell migration, axon-bundle formation, target-cell recognition, activity-dependent plasticity of synapses, and formation of complex glial networks, which surround axons and synapses (1). Nectins are a novel family of Ca 2ϩ -independent immunoglobulin-like cell-cell adhesion molecules and comprise four members, termed Nectin-1 to Nectin-4 (2, 3). All Nectins have an extracellular region of three Ig-like domains, a single transmembrane region, and a cytoplasmic tail region (see Fig. 1) (2, 3). Each Nectin forms a homo-cis-dimer, in which the monomers are aligned in a parallel orientation, which is then followed by formation of homo-trans-dimers in which cis-dimers from opposing cell surfaces interact in an anti-parallel orientation, causing cell-cell adhesion (4 -8).The first Ig-like domain is necessary and sufficient for the formation of homo-trans-dimers, whereas the second Ig-like domain is necessary for the formation of homo-cis-dimers (5, 7-9). Furthermore, Nectin-3 can also form a hetero-trans-dimer with either Nectin-1 or -2, whereas Nectin-4 also forms a hetero-trans-dimer with Nectin-1 (4). The heterotrans-dimers are also mediated by the V domains (9). Nectin-1 has been confirmed to serve as a receptor for all ␣-herpes viruses tested so far, including herpes simplex virus (HSV) 3 type 1, HSV type 2, and pseudorabies virus, facilitating their entry and cell-cell spread (10, 11). Furthermore, the V domain of Nectin-1 has been demonstrated to play a central role in the interaction with the envelope glycoprotein D of HSV, pseudorabies virus, and bovine herpes virus-1 (12, 13). Therefore, the V domain plays an essential role not only in homophilic and heterophilic trans-interactions but ...

Binding of herpes simplex virus glycoprotein D to nectin-1 exploits host cell adhesion

“…Narita et al 21 argued in their model of diff erential dimer formats for cishomodimer and trans -homodimer of nectin-1 that the perpendicular interaction (almost 90 ° between the two molecules) of nectin-1 dimer can only assist cis -interaction (on the same cell surface) because there is not enough angles for two cells to interact in their trans -dimer. Th is notion is indirectly supported by a dimeric structure of Necl-1 in that the two molecules formed a more open angle (approximately 110 ° ) 35 , which is believed to represent a trans -dimer of the family. Th e two crystal structures (free and complex) of the three Ig domains of nectin-1 in our study and the earlier reported structure 21 show that the hinge region between the second Ig-like domain and the third Iglike domain of nectin-1 has some fl exibility, unlike the hinge between the domains 1 and 2.…”

Crystal Structure of Cell Adhesion Molecule Nectin-2/CD112 and Its Binding to Immune Receptor DNAM-1/CD226

“…The structures of nectin-1 (three Ig domains) (54), Necl-1 (V domain alone) (36), and Necl-3 (V domain alone) (38) reveal that these molecules also form dimers through the interaction of their V domains. By superimposing nectin-2 on nectin-1, we found that the overall conformation of the dimer formed by nectin-2v is similar to nectin-1, with the root mean square deviation (RMSD) of 1.472 Å (Fig.…”

“…Only three homodimers (three Ig domains of nectin-1, one Ig domain of Necl-1 and Necl-3) and one monomer (two Ig domains of Necl-5) of nine members of this family have been described but with different conclusions (36,38,54,55). The structure of nectin-1 is regarded as a cis-dimer, but Necl-1 is considered a trans-dimer (36,38,54). There is no structural report of any heterodimers for these family members.…”

Structure of TIGIT immunoreceptor bound to poliovirus receptor reveals a cell–cell adhesion and signaling mechanism that requires cis-trans receptor clustering

“…Several high-affinity homophilic trans-interactions have been described in detail for nectins/Necls and similar molecules (8)(9)(10)(11)(12)(13). However, the structure and function of the presumably weaker lateral homophilic cis-dimers in cell adhesion and their role in intracellular signaling is not known.…”

“…Nectins and Necls can function as both ligands and receptors and therefore are able to signal bidirectionally into juxtaposed cells (3,6). To mediate the formation of cell adherens junctions, a model suggests that the extracellular domains of these molecules form ligand-dependent homo-or heterodimers in trans (between molecules located on the same or opposite cell surfaces, respectively) and lateral homodimers in cis, creating a tight network of nectin zippers between juxtaposed cells (7,8). To date, structural and functional studies suggest a mechanism whereby the cis-homodimerization of a receptor on the same cell surface is followed by the formation of a trans-dimer between juxtaposed cells using identical protein interfaces.…”