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Structural basis for variant-specific neuroligin-binding by α-neurexin.
Hiroki Tanaka1, Terukazu Nogi, Norihisa Yasui
1Laboratory of Protein Synthesis and Expression, Institute for Protein Research, Osaka University, Suita, Osaka, Japan.
Plos One
|May 10, 2011
Summary
Neurexin (Nrx) structures reveal how alpha-Nrx variants bind neuroligins differently. This explains how Nrx adhesion impacts synaptic function and structure.
Area of Science:
- Neuroscience
- Structural Biology
- Molecular Biology
Background:
- Neurexins (Nrxs) are presynaptic proteins crucial for synaptic adhesion, binding to postsynaptic neuroligins.
- Alpha-Nrx and beta-Nrx isoforms exhibit distinct neuroligin binding behaviors, yet the structural basis remains unclear.
- Alpha-Nrx possesses an extended extracellular region with multiple LNS and EGF domains, unlike the simpler beta-Nrx.
Purpose of the Study:
- To elucidate the structural mechanism underlying the differential binding of alpha-Nrx to neuroligin variants.
- To determine the structure of a key fragment of the Nrx1α ectodomain and model the full ectodomain.
Main Methods:
- X-ray crystallography of the Nrx1α ectodomain fragment (LNS5-EGF3-LNS6) at 2.3 Å resolution.
- Single-particle reconstruction of full-length Nrx1α using negative staining electron microscopy.
- Comparative analysis of domain configurations and neuroligin-binding site accessibility.
Main Results:
- The Nrx1α fragment adopted a rigidified conformation due to inter-domain contacts, deviating from a flexible 'beads-on-a-string' model.
- The neuroligin-binding site on LNS6 was accessible, but the adjacent LNS5-EGF3 segment sterically hindered binding to neuroligin B+ variants.
- A structural model of the full α-Nrx ectodomain was generated, integrating crystal structure and electron microscopy data.
Conclusions:
- The unique domain arrangement of α-Nrx, specifically the LNS5-EGF3 segment, explains its variant-specific neuroligin recognition.
- The structural model provides insights into how the large α-Nrx ectodomain fits within the synaptic cleft.
- Differential trans-synaptic adhesion mediated by α- and β-Nrxs likely influences synaptic structure and function.
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