Zinc-chelating postsynaptic density-95 N-terminus impairs its palmitoyl modification

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Chemical synaptic transmission relies on precise neurotransmitter balance, with imbalances linked to neuronal degeneration.
• Intracellular zinc accumulation is observed in degenerating neurons, but the mechanisms are unclear.
• Postsynaptic density protein-95 (PSD-95) is crucial for excitatory synapse development and maturation, with its membrane association regulated by palmitoylation.

Purpose of the Study:

• To investigate the interaction between zinc ions (Zn²⁺) and the N-terminal region of PSD-95 (PSD-95NT).
• To determine the functional consequences of Zn²⁺ binding on PSD-95 palmitoylation and postsynaptic localization.

Main Methods:

• Nuclear Magnetic Resonance (NMR) titration of ¹⁵N-labeled PSD-95NT with ZnCl₂.
• Fluorescence and mutagenesis assays to confirm zinc binding and identify critical residues.
• Mimic palmitoyl modification and intact cell palmitoylation assays to assess the impact on PSD-95 palmitoylation.

Main Results:

• Zn²⁺ binds to PSD-95NT with a micromolar affinity, involving specific cysteine and histidine residues (C3/C5, H24/H28).
• The zinc binding site on PSD-95NT overlaps with its palmitoylation sites.
• Zinc binding was shown to influence PSD-95 palmitoylation in a concentration-dependent manner.

Conclusions:

• Zinc acts as a novel modulator of PSD-95 postsynaptic membrane association by binding to its N-terminal region.
• This zinc-mediated regulation of PSD-95 palmitoylation has significant implications for postsynaptic signaling.
• Understanding this interaction may provide insights into mechanisms underlying neuronal health and disease.