Cbln1 and Cbln4 Are Structurally Similar but Differ in GluD2 Binding Interactions.
Chen Zhong1, Jinlong Shen1, Huibing Zhang1
1National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Center for Excellence in Molecular Cell Science, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, P.R. China.
Cell Reports
|September 7, 2017
Summary
Cerebellin 4 (Cbln4) binds neurexin (Nrxn1β), unlike cerebellin 1 (Cbln1). Structural analysis reveals distinct binding mechanisms, offering insights into synaptic connections and Cbln protein function.
Area of Science:
- Neuroscience
- Structural Biology
- Molecular Biology
Background:
- Cerebellin 1 (Cbln1) facilitates synaptic connections by bridging neurexin (Nrxn) and glutamate receptors.
- Cbln4 shares high sequence identity with Cbln1 but exhibits weak or no binding to glutamate receptors.
- Understanding Cbln4's molecular interactions is crucial for elucidating synaptic organization.
Purpose of the Study:
- To determine the structural basis for differential binding of Cbln1 and Cbln4 to synaptic receptors.
- To investigate the interaction between Cbln4 and neurexin 1 beta (Nrxn1β).
Main Methods:
- X-ray crystallography was used to obtain high-resolution structures of Cbln1 and Cbln4 C1q domains.
- Negative-stain electron microscopy was employed to reconstruct Cbln1 and Cbln4/Nrxn1β complexes.
Main Results:
- Crystal structures revealed sequence and structural divergence in loop CD between Cbln1 and Cbln4, potentially explaining differences in GluD2 binding.
- Cbln4 was found to bind Nrxn1β, forming a stable complex with its laminin, nectin, sex-hormone binding globulin (LNS) domain.
- Electron microscopy suggested Nrxn1β interacts with the N-terminal region of Cbln4 via strand β10 of the S4 insert.
Conclusions:
- Cbln4 exhibits distinct binding properties compared to Cbln1, interacting with Nrxn1β.
- Structural differences in loop CD are implicated in the differential binding to GluD2 receptors.
- These findings provide novel insights into the molecular mechanisms governing Cbln-mediated synaptic interactions.
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