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: 15.05). 01/2008; 56(6):992-1003. DOI: 10.1016/j.neuron.2007.12.002
Source: PubMed


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,
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    • "Neuroligins bind to neurexins in a trans-configuration to form an intercellular junction (Nguyen and Sü dhof, 1997) and also interact with other cis-and transligands (Ko et al., 2009a, 2009b; Lee et al., 2013; Pettem et al., 2013). Preliminary analyses suggest that different neuroligin-neurexin combinations exhibit distinct binding affinities depending on the precise isoforms and splice variants involved (Boucard et al., 2005; Chih et al., 2006; Comoletti et al., 2006; Araç et al., 2007), although no systematic comparisons have been performed. Human neuroligin gene mutations appear to cause autism and/or intellectual disability with nearly 100% penetrance, usually as de novo mutations arising in the germline (reviewed in Chen et al., 2014; Sü dhof, 2008). "
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    ABSTRACT: Neuroligins are postsynaptic cell-adhesion molecules that bind presynaptic neurexins and are genetically linked to autism. Neuroligins are proposed to organize synaptogenesis and/or synaptic transmission, but no systematic analysis of neuroligins in a defined circuit is available. Here, we show that conditional deletion of all neuroligins in cerebellar Purkinje cells caused loss of distal climbing-fiber synapses and weakened climbing-fiber but not parallel-fiber synapses, consistent with alternative use of neuroligins and cerebellins as neurexin ligands for the excitatory climbing-fiber versus parallel-fiber synapses. Moreover, deletion of neuroligins increased the size of inhibitory basket/stellate-cell synapses but simultaneously severely impaired their function. Multiple neuroligin isoforms differentially contributed to climbing-fiber and basket/stellate-cell synapse functions, such that inhibitory synapse-specific neuroligin-2 was unexpectedly essential for maintaining normal climbing-fiber synapse numbers. Using systematic analyses of all neuroligins in a defined neural circuit, our data thus show that neuroligins differentially contribute to various Purkinje-cell synapses in the cerebellum in vivo. Copyright © 2015 Elsevier Inc. All rights reserved.
    Neuron 08/2015; 87(4). DOI:10.1016/j.neuron.2015.07.020 · 15.05 Impact Factor
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    • "The shorter isoform is generated from an alternative internal promoter in the same locus. To test if NRX-1 clusters NLG-1, we introduced three analogous missense mutations in NLG-1 that are predicted to abolish its putative binding sites for b-neurexin (Araç et al., 2007) and expressed the corresponding protein, "
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    ABSTRACT: At synapses, the presynaptic release machinery is precisely juxtaposed to the postsynaptic neurotransmitter receptors. We studied the molecular mechanisms underlying this exquisite alignment at the C. elegans inhibitory synapses. We found that the sole C. elegans neuroligin homolog, NLG-1, localizes specifically at GABAergic postsynapses and is required for clustering the GABAA receptor UNC-49. Two presynaptic factors, Punctin/MADD-4, an ADAMTS-like extracellular protein, and neurexin/NRX-1, act partially redundantly to recruit NLG-1 to synapses. In the absence of both MADD-4 and NRX-1, NLG-1 and GABAA receptors fail to cluster, and GABAergic synaptic transmission is severely compromised. Biochemically, we detect an interaction between MADD-4 and NLG-1, as well as between MADD-4 and NRX-1. Interestingly, the presence of NRX-1 potentiates binding between Punctin/MADD-4 and NLG-1, suggestive of a tripartite receptor ligand complex. We propose that presynaptic terminals induce postsynaptic receptor clustering through the action of both secreted ECM proteins and trans-synaptic adhesion complexes. Copyright © 2015 Elsevier Inc. All rights reserved.
    Neuron 05/2015; 86(6). DOI:10.1016/j.neuron.2015.05.015 · 15.05 Impact Factor
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    • "Like AChE, the ectodomain of neuroligin-1 also possesses surface anionic residues. Given that binding of the ectodomain of neuroligin-1 to neurexin-1β occurs on the side opposite to the surface anionic residues [52], we propose that AChE similarly interacts with β-neurexins through a region on the opposite side of the surface anionic residues (see Figure  9). Physostigmine, an AChE inhibitor that binds to enzymatic residues in the gorge of AChE, also increased the interaction between neurexin-1β and AChE-S (Figures  4D and E). "
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    ABSTRACT: Excess expression of acetylcholinesterase (AChE) in the cortex and hippocampus causes a decrease in the number of glutamatergic synapses and alters the expression of neurexin and neuroligin, trans-synaptic proteins that control synaptic stability. The molecular sequence and three-dimensional structure of AChE are homologous to the corresponding aspects of the ectodomain of neuroligin. This study investigated whether excess AChE interacts physically with neurexin to destabilize glutamatergic synapses. The results showed that AChE clusters colocalized with neurexin assemblies in the neurites of hippocampal neurons and that AChE co-immunoprecipitated with neurexin from the lysate of these neurons. Moreover, when expressed in human embryonic kidney 293 cells, N-glycosylated AChE co-immunoprecipitated with non-O-glycosylated neurexin-1beta, with N-glycosylation of the AChE being required for this co-precipitation to occur. Increasing extracellular AChE decreased the association of neurexin with neuroligin and inhibited neuroligin-induced synaptogenesis. The number and activity of excitatory synapses in cultured hippocampal neurons were reduced by extracellular catalytically inactive AChE. Excessive glycosylated AChE could competitively disrupt a subset of the neurexin-neuroligin junctions consequently impairing the integrity of glutamatergic synapses. This might serve a molecular mechanism of excessive AChE induced neurodegeneration.
    Molecular Brain 03/2014; 7(1):15. DOI:10.1186/1756-6606-7-15 · 4.90 Impact Factor
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