Specific Interaction of Postsynaptic Densities With Membrane Rafts Isolated From Synaptic Plasma Membranes

Abstract

Postsynaptic membrane rafts are believed to play important roles in synaptic signaling, plasticity, and maintenance. We recently demonstrated the presence, at the electron microscopic level, of complexes consisting of membrane rafts and postsynaptic densities (PSDs) in detergent-resistant membranes (DRMs) prepared from synaptic plasma membranes (SPMs) ( Suzuki et al., 2011 , J Neurochem, 119, 64-77). To further explore these complexes, here we investigated the nature of the binding between purified SPM-DRMs and PSDs in vitro. In binding experiments, we used SPM-DRMs prepared after treating SPMs with n-octyl-β-d-glucoside, because at concentrations of 1.0% or higher it completely separates SPM-DRMs and PSDs, providing substantially PSD-free unique SPM-DRMs as well as DRM-free PSDs. PSD binding to PSD-free DRMs was identified by mass spectrometry, Western blotting, and electron microscopy. PSD proteins were not incorporated into SPMs, and significantly less PSD proteins were incorporated into DRMs prepared from liver membranes, providing in vitro evidence that binding of PSDs to DRMs is specific and suggestion of the presence of specific interacting molecules. These specific interactions may have important roles in synaptic development, function, and plasticity in vivo. In addition, the binding system we developed may be a good tool to search for binding molecules and binding mechanisms between PSDs and rafts.

Lipid rafts: a signaling platform linking cholesterol metabolism to synaptic deficits in autism spectrum disorders

“…(B) Representative autism linked signaling proteins which are associated with lipid rafts. There is an increasing overlapping between affected signaling molecules or pathways in ASDs and lipid raft associated synaptic proteins as revealed by studies in autism genetics (Huguet et al, 2013; Murdoch and State, 2013; Persico and Napolioni, 2013; Schmunk and Gargus, 2013; Krumm et al, 2014; Ronemus et al, 2014) and neurobiology (Wang et al, 2008b, 2010; Zoghbi and Bear, 2012; Delorme et al, 2013; Ebert and Greenberg, 2013; Won et al, 2013) as well as research in lipid rafts (Allen et al, 2007; Korade and Kenworthy, 2008; Pristera and Okuse, 2011; Suzuki et al, 2011; Sebastiao et al, 2012; Liu et al, 2013). These studies further support the functional link between lipid rafts and synaptic deficits in ASDs.…”

“…Lipid rafts not only contribute to neurotransmitter exocytosis in presynaptic terminals, but also postsynapticly modulate neuronal signaling through clustering of neurotransmitter receptors, ion channels and components of downstream effectors (Tsui-Pierchala et al, 2002; Korade and Kenworthy, 2008; Linetti et al, 2010; Pfrieger and Ungerer, 2011; Pristera and Okuse, 2011; Sebastiao et al, 2012) (Figure 1A). The postsynaptic density (PSD), which is a massive multi-protein complex whose functions include positioning signaling molecules for synaptic plasticity, could be physically associated with lipid rafts (Hering et al, 2003; Sheng and Hoogenraad, 2007; Delint-Ramirez et al, 2010; Sheng and Kim, 2011; Suzuki et al, 2011; Liu et al, 2013). Numerous PSD proteins such as NMDA receptors (NR1, NR2A and NR2B), AMPA receptors (GluR1 and GluR2), metabotropic glutamate receptors (mGluRs), PSD-93/95, CaMKII, and cadherin, are associated with synaptic lipid rafts; notably, PSD-95 binds to the postsynaptic neuroligins which interact with the presynaptic neurexins, providing a transsynaptic link between PSD and presynaptic active zone (Hering et al, 2003; Delint-Ramirez et al, 2010; Sheng and Kim, 2011; Suzuki et al, 2011; Liu et al, 2013).…”

Molecular and structural bases for postsynaptic signal processing: interaction between postsynaptic density and postsynaptic membrane rafts

“…Identification of PSD-PSR complexes is possible also due to the unique properties of TX-100, which is weak in disrupting raft-cytoskeleton interactions. [29][30][31] On the contrary, β-octyl-D-glucoside (OG) completely disassociates PSD structures from PSRs and leaves DRMs with only a few raftrelated proteins. This complete separation observed in OG treatment may be explained by the presence, at the margin of each raft domain, of a lipid environment that is sensitive to OG extraction, as suggested by the lipid-shell hypothesis.…”

“…Purified PSDs appear to bind specifically with purified SPMDRMs, because the PSDs do not bind with SPM and show significantly lower level of binding to DRMs derived from liver membranes. 30 This suggests the presence of specific binding molecules and mechanisms for interactions between PSDs and PSRs, although details are currently unknown. There are several ways for proteins to target raft domains in the plasma membrane through protein-protein and proteinlipid interactions.…”

“…97 Roles of membrane rafts in synaptogenesis may, at least partly, be due to the presence of many synaptic cell adhesion molecules. 28,30 Some of these cell adhesion molecules work as synapse organizers. 98,99 Specific cell adhesion molecules accumulate at pre-and postsynaptic sites and trigger synapse formation.…”