Synaptic GAP and GEF Complexes Cluster Proteins Essential for GTP Signaling

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Signaling

Background:

• Guanine nucleotide-binding protein (GTPase)-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs) regulate small GTPase activity.
• These proteins are found at the postsynaptic density (PSD) of excitatory neurons, influencing glutamate receptor activity.
• The organization and interaction networks of synaptic GAPs and GEFs, and their links to psychiatric disorders, remain largely unknown.

Purpose of the Study:

• To investigate the interactomes of three key PSD-localized GAP/GEF proteins: Syngap1 (RasGAP), Agap2 (ArfGAP), and Kalirin (RhoGEF).
• To determine the functional properties and clustering of GTPase signaling proteins within these interactomes.
• To explore the subcellular localization and functional diversity of Agap2, and its association with proteins implicated in psychiatric diseases.

Main Methods:

• Proteomic analysis to identify protein-protein interactions (interactomes) for Syngap1, Agap2, and Kalirin at the PSD.
• Analysis of an additional 110 interactions for Agap2 outside the PSD.
• Functional enrichment analysis of identified interactomes.

Main Results:

• Identified a total of 280 interactions for the three PSD GAP/GEF proteins.
• Demonstrated that these GAP/GEF proteins significantly associate with and cluster other GTPase signaling proteins.
• Revealed common and distinct functions for Agap2 based on its PSD and non-PSD localization.
• Found associations between these GAPs/GEFs and proteins linked to psychiatric disorders.

Conclusions:

• Synaptic GAPs and GEFs form complex signaling hubs at the PSD, primarily organizing GTPase signaling machinery.
• Subcellular localization dictates the specific functions of proteins like Agap2.
• These synaptic regulators represent potential molecular links between GTPase signaling and psychiatric disease pathogenesis.