Structures of Neuroligin-1 and the Neuroligin-1/Neurexin-1β Complex Reveal Specific Protein-Protein and Protein-Ca2+ Interactions

Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA.
Neuron (Impact Factor: 15.98). 01/2008; 56(6):992-1003. DOI: 10.1016/j.neuron.2007.12.002
Source: PubMed

ABSTRACT Neurexins and neuroligins provide trans-synaptic connectivity by the Ca2+-dependent interaction of their alternatively spliced extracellular domains. Neuroligins specify synapses in an activity-dependent manner, presumably by binding to neurexins. Here, we present the crystal structures of neuroligin-1 in isolation and in complex with neurexin-1 beta. Neuroligin-1 forms a constitutive dimer, and two neurexin-1 beta monomers bind to two identical surfaces on the opposite faces of the neuroligin-1 dimer to form a heterotetramer. The neuroligin-1/neurexin-1 beta complex exhibits a nanomolar affinity and includes a large binding interface that contains bound Ca2+. Alternatively spliced sites in neurexin-1 beta and in neuroligin-1 are positioned nearby the binding interface, explaining how they regulate the interaction. Structure-based mutations of neuroligin-1 at the interface disrupt binding to neurexin-1 beta, but not the folding of neuroligin-1 and confirm the validity of the binding interface of the neuroligin-1/neurexin-1 beta complex. Our results provide molecular insights for understanding the role of cell-adhesion proteins in synapse function.

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Available from: Antony A Boucard, Aug 14, 2015
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    • "The crystal structure of the Nrx1b/NL1 complex determined at 3.3 A ˚ resolution comprises a heterotetramer in which two Nrx1b protomers bind to distal ends of a NL1 homodimer (Figure 1A; Table 1). This 2:2 arrangement, as well as the recognition mode that involves intermolecular hydrogen-bonding network and Nrx1b- bound Ca 2+ (Figure S1A), is identical to that seen in the previously reported crystal structures of Nrx1b/NL1 (Araç et al., 2007; Chen et al., 2008) and Nrx1b/NL4 (Fabrichny et al., 2007) complexes. Moreover, we could see clear electron density for SpA insertion in one of the NL1 molecules (Figure S1B). "
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    ABSTRACT: Polymorphic adhesion molecules neurexin and neuroligin (NL) mediate asymmetric trans-synaptic adhesion, which is crucial for synapse development and function. It is not known whether or how individual synapse function is controlled by the interactions between variants and isoforms of these molecules with differing ectodomain regions. At a physiological concentration of Ca(2+), the ectodomain complex of neurexin-1 β isoform (Nrx1β) and NL1 spontaneously assembled into crystals of a lateral sheet-like superstructure topologically compatible with transcellular adhesion. Correlative light-electron microscopy confirmed extracellular sheet formation at the junctions between Nrx1β- and NL1-expressing non-neuronal cells, mimicking the close, parallel synaptic membrane apposition. The same NL1-expressing cells, however, did not form this higher-order architecture with cells expressing the much longer neurexin-1 α isoform, suggesting a functional discrimination mechanism between synaptic contacts made by different isoforms of neurexin variants.
    Cell Reports 07/2012; 2(1):101-10. DOI:10.1016/j.celrep.2012.06.009 · 8.36 Impact Factor
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    • "The previously described NLGN binding site on LNS 6 is solvent accessible in the stabilized conformation found in the α-NRXN_2-6 structure. To model the complex between α-NRXN and NLGN-1, we superimposed the structure of α-NRXN_2-6 onto the structures of the β-NRXN-1 molecules bound to NLGN-1 (Arac et al., 2007). The overlaid NLGN molecule interfaces with the α- NRXN_2-6 molecule without significant steric obstruction, indicating that NLGN could bind to α-NRXN_2-6 in the crystallized conformation (Figure 4A). "
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    ABSTRACT: α- and β-neurexins (NRXNs) are transmembrane cell adhesion proteins that localize to presynaptic membranes in neurons and interact with the postsynaptic neuroligins (NLGNs). Their gene mutations are associated with the autism spectrum disorders. The extracellular region of α-NRXNs, containing nine independently folded domains, has structural complexity and unique functional characteristics, distinguishing it from the smaller β-NRXNs. We have solved the X-ray crystal structure of seven contiguous domains of the α-NRXN-1 extracellular region at 3.0 Å resolution. The structure reveals an arrangement where the N-terminal five domains adopt a more rigid linear conformation and the two C-terminal domains form a separate arm connected by a flexible hinge. In an extended conformation the molecule is suitably configured to accommodate a bound NLGN molecule, as supported by structural comparison and surface plasmon resonance. These studies provide the structural basis for a multifunctional synaptic adhesion complex mediated by α-NRXN-1.
    Structure 06/2011; 19(6):767-78. DOI:10.1016/j.str.2011.03.011 · 6.79 Impact Factor
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    • "The assemblies that are formed in this way are likely to provide templates for the recruitment of cytoplasmic proteins, which may then initiate downstream signaling events. Although the structures of individual trans dimers of numerous adhesion proteins have now been revealed (Arac et al., 2007; Boggon et al., 2002; Somers et al., 2000), atomic level structures of larger assemblies have not been determined. Here, we present crystal structures of the complete ectodomains of E-and N-cadherins and show that their crystals share a common molecular layer that is formed by a similar array of cis and trans interactions. "
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