Intramolecular domain dynamics regulate synaptic MAGUK protein interactions.

Nils Rademacher,Christian Freund,Benno Kuropka,Stella-Amrei Kunde,Sarah A Shoichet,Markus C Wahl

doi:10.7554/elife.41299

Abstract

PSD-95 MAGUK family scaffold proteins are multi-domain organisers of synaptic transmission that contain three PDZ domains followed by an SH3-GK domain tandem. This domain architecture allows coordinated assembly of protein complexes composed of neurotransmitter receptors, synaptic adhesion molecules and downstream signalling effectors. Here we show that binding of monomeric CRIPT-derived PDZ3 ligands to the third PDZ domain of PSD-95 induces functional changes in the intramolecular SH3-GK domain assembly that influence subsequent homotypic and heterotypic complex formation. We identify PSD-95 interactors that differentially bind to the SH3-GK domain tandem depending on its conformational state. Among these interactors, we further establish the heterotrimeric G protein subunit Gnb5 as a PSD-95 complex partner at dendritic spines of rat hippocampal neurons. The PSD-95 GK domain binds to Gnb5, and this interaction is triggered by CRIPT-derived PDZ3 ligands binding to the third PDZ domain of PSD-95, unraveling a hierarchical binding mechanism of PSD-95 complex formation.

Highlights

Excitatory synapses are the contact sites through which neurons communicate with each other
We have previously shown that the synaptic membrane-associated guanylate kinases (MAGUKs) protein postsynaptic density (PSD)-95 oligomerises upon binding of monomeric CRIPT-derived PDZ3 ligands (Rademacher et al, 2013) and speculated that ligand - PDZ3 domain binding induces conformational changes in the C-terminal domains that lead to complex formation
We built on our previous work with tagged cytosolic CRIPT-derived PDZ3 ligands (Rademacher et al, 2013) and we have designed a cell-based assay to directly monitor the proximity of PSD-95 molecules by bimolecular fluorescence complementation (BiFC)

Summary

Introduction

Excitatory synapses are the contact sites through which neurons communicate with each other These synapses are asymmetric structures that are formed by pre- and postsynaptic terminals containing distinct sets of proteins. Incoming action potentials are converted into chemical signals (neurotransmitters) at presynaptic terminals, which subsequently pass through the synaptic cleft and are reconverted into electrical signals at postsynaptic sites (Lisman et al, 2007). These synaptic contacts are not static but are able to undergo structural changes and thereby modify neuronal network computation (Nishiyama and Yasuda, 2015). The PSD-95 GK domain is atypical in that it is unable to phosphorylate GMP but has evolved as a protein interaction domain

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