α-Actinin Anchors PSD-95 at Postsynaptic Sites

Abstract

Despite the central role PSD-95 plays in anchoring postsynaptic AMPARs, how PSD-95 itself is tethered to postsynaptic sites is not well understood. Here we show that the F-actin binding protein α-actinin binds to the very N terminus of PSD-95. Knockdown (KD) of α-actinin phenocopies KD of PSD-95. Mutating lysine at position 10 or lysine at position 11 of PSD-95 to glutamate, or glutamate at position 53 or glutamate and aspartate at positions 213 and 217 of α-actinin, respectively, to lysine impairs, in parallel, PSD-95 binding to α-actinin and postsynaptic localization of PSD-95 and AMPARs. These experiments identify α-actinin as a critical PSD-95 anchor tethering the AMPAR-PSD-95 complex to postsynaptic sites.

Subsynaptic spatial organization as a regulator of synaptic strength and plasticity

“…Alternatively, regulation of receptor-anchoring PSD proteins may be required to drive receptor exchange in local regions of the synapse. Indeed, multiple mechanisms control PSD-95 abundance, including phosphorylation [27], palmitoylation [13] and direct binding to the actin modulator α-actinin [28]. Because PSD-95 displays such limited intra-PSD mobility [29, [30], spatially restricted modification of the scaffold may be a mechanism for nanoscale remodeling of receptor distribution.…”

Postsynaptic localization and regulation of AMPA receptors and Cav1.2 by β2 adrenergic receptor/PKA and Ca 2+ /CaMKII signaling

“…SAP97 is likely not more abundant than PSD‐93 or SAP102 given its relatively low apparent synaptic enrichment by immunofluorescence microscopy (Valtschanoff et al, ). PSD‐95 in turn is localized to the synapse by α‐actinin binding to the N‐terminus of PSD‐95 (Matt et al, ). Postsynaptic targeting of PSD‐95 also requires its palmitoylation of Cys3 and Cys5 near its N‐terminus (Craven et al, ; El‐Husseini Ael et al, ).…”

“…α‐Actinin binding to PSD‐95 is not only important for the localization of PSD‐95 but also of a substantial fraction (~40%) of AMPARs. Postsynaptic localization of most of the remaining AMPARs depends on PSD‐93 and SAP102 (Elias et al, , ), which do not bind to α‐actinin and are anchored at postsynaptic sites independent of α‐actinin (Matt et al, ). The estimated presence of ~400 molecules PSD‐95 and its homologues fits remarkably well with affinity determinations for PDZ interactions specifically for the interaction of the first two PDZ domains of PSD‐95 with GluN2 subunits and TARPs.…”

“…GluN2A and 2B bind directly with their C‐termini to these PDZ domains (Kornau et al, ) and removal of PSD‐95 and its homologues reduces excitatory postsynaptic currents (EPSCs) by NMDARs, suggesting that these scaffolds contribute channel functional availability (Elias et al, , ; Ehrlich et al, ; Fig ). However, PDZ interactions appear less critical for postsynaptic availability of NMDARs than of AMPARs as NMDAR EPSCs are less sensitive to a reduction in PSD‐93/95 (Elias et al, , ; Schluter et al, ; Ehrlich et al, ; Matt et al, ) or mutations that affect PDZ binding (Schnell et al, ; Prybylowski et al, ). Nevertheless, acute disruption of PDZ binding does strongly increase lateral mobility of synaptic NMDARs (Bard et al, ), as it does increase diffusion of AMPARs (Sainlos et al, ).…”

“…This interaction antagonizes palmitoylation of PSD‐95 on Cys3 and Cys5, which is required for its postsynaptic localization and reversed upon NMDAR activation (El‐Husseini Ael et al, ; Zhang et al, ). Ca 2+ /CaM recruitment to the PSD‐95 N‐terminus also displaces α‐actinin (Matt et al, ), which anchors PSD‐95 at the postsynaptic site (Matt et al, ). Mutating Tyr12 near the N‐terminus of PSD‐95 to Glu not only abrogates Ca 2+ /CaM binding and with it loss of PSD‐95(Y12E) from spines but actually causes a substantial increase in postsynaptic accumulation of this PSD‐95 mutant in spines upon Ca 2+ influx.…”