Which ONE statement about the post-synaptic specialization of excitatory synapses in the brain is correct?

Question

BlackTom AI · Accepted Answer

Neuroligin-1 is a postsynaptic cell-adhesion protein at excitatory synapses that binds presynaptic neurexins across the synaptic cleft, and this trans-synaptic complex aligns postsynaptic receptor clusters (the postsynaptic density, PSD) with presynaptic release machinery (active zone). That molecular linkage is the key concept behind the correct statement.

1. Relevant knowledge points and concepts
- Synapses have a postsynaptic density (PSD) rich in scaffolding proteins (e.g., PSD-95) that cluster glutamate receptors, and a presynaptic active zone where vesicle release occurs.
- Trans-synaptic adhesion molecules (neurexins on the presynaptic side; neuroligins on the postsynaptic side) form physical and signaling links that organize and align pre- and postsynaptic specializations.
- Neuroligin-1 is enriched at excitatory (glutamatergic) synapses; its intracellular PDZ-binding motif binds PSD-95, coupling adhesion to receptor/scaffold clustering. Neurexin-1β interacts with presynaptic active zone components (via CASK, etc.) to organize release sites.

2. Step-by-step reasoning
- Neuroligin-1 extracellular domain binds neurexin-1β across the cleft, forming a trans-synaptic adhesion complex.
- The intracellular tail of neuroligin-1 recruits PSD-95 and related scaffold proteins, consolidating AMPA/NMDA receptor clusters at the PSD.
- Neurexin complexes recruit/organize active zone proteins that define vesicle docking and release sites.
- The trans-synaptic bridge therefore positions release sites opposite receptor-dense PSDs, functionally “anchoring” presynaptic release locations to postsynaptic specializations.

3. Intermediate steps / evidence
- Genetic or acute disruption of neuroligin–neurexin interactions reduces synapse alignment and synaptic efficacy; super-resolution and EM studies show nanocolumn alignment dependent on adhesion molecules.
- Neuroligin-1 preference for excitatory synapses (vs neuroligin-2 at inhibitory synapses) explains specificity.

4. Why the correct answer is correct
- The statement correctly names neuroligin-1 (postsynaptic) and neurexin-1β (presynaptic) and correctly describes their role in anchoring/aligning release sites with the PSD via scaffold interactions.

5. Why other plausible alternatives would be incorrect
- Claiming neurexin is postsynaptic or neuroligin presynaptic is reversed and wrong.
- Saying gephyrin or neuroligin-2 anchor excitatory PSDs is incorrect: gephyrin and neuroligin-2 are associated with inhibitory synapses.
- Claims that integrins or extracellular matrix alone determine alignment ignore the evidence for neurexin–neuroligin-mediated trans-synaptic organization.

6. Conclusion
This reasoning confirms the provided correct answer: Release sites in the presynaptic membrane are anchored to the location of the postsynaptic density by the binding of the postsynaptic cell adhesion molecule neuroligin 1 to the presynaptic protein neurexin 1β.

Which ONE statement about the post-synaptic specialization of excitatory synapses in the brain is correct?Single choice

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