Capping of the N-terminus of PSD-95 by calmodulin triggers its postsynaptic release

Abstract

Postsynaptic density protein-95 (PSD-95) is a central element of the postsynaptic architecture of glutamatergic synapses. PSD-95 mediates postsynaptic localization of AMPA receptors and NMDA receptors and plays an important role in synaptic plasticity. PSD-95 is released from postsynaptic membranes in response to Ca 2+ influx via NMDA receptors. Here, we show that Ca 2+ /calmodulin (CaM) binds at the N-terminus of PSD-95. Our NMR structure reveals that both lobes of CaM collapse onto a helical structure of PSD-95 formed at its N-terminus (residues 1-16). This N-terminal capping of PSD-95 by CaM blocks palmitoylation of C3 and C5, which is required for postsynaptic PSD-95 targeting and the binding of CDKL5, a kinase important for synapse stability. CaM forms extensive hydrophobic contacts with Y12 of PSD-95. The PSD-95 mutant Y12E strongly impairs binding to CaM and Ca 2+ -induced release of PSD-95 from the postsynaptic membrane in dendritic spines. Our data indicate that CaM binding to PSD-95 serves to block palmitoylation of PSD-95, which in turn promotes Ca 2+ -induced dissociation of PSD-95 from the postsynaptic membrane.

α-Actinin Promotes Surface Localization and Current Density of the Ca2+ Channel CaV1.2 by Binding to the IQ Region of the α1 Subunit

“…To evaluate whether these mutations affected binding of apoCaM we utilized a fluorescence polarization (FP) assay we had adopted earlier for defining CaM binding (52) to evaluate the relative binding-affinities of the WT and mutant α 1 1.2 IQ domains for apoCaM (Fig. 4; Table 1).…”

Ca 2+ /calmodulin binding to PSD ‐95 mediates homeostatic synaptic scaling down

“…We recently found that Ca 2+ /CaM also binds to the N‐terminal 16 residues of PSD‐95 (Zhang et al , ). We showed by NMR structural analysis that both CaM lobes collapse around a helix formed by PSD‐95 residues 1–14 (Zhang et al , ). This interaction shields two palmitoylation sites (C3 and C5) that are crucial for postsynaptic targeting of PSD‐95.…”

“…This interaction shields two palmitoylation sites (C3 and C5) that are crucial for postsynaptic targeting of PSD‐95. Y12 in PSD‐95 makes the most contacts with Ca 2+ /CaM (Zhang et al , ). The Y12E mutation abrogates binding of Ca 2+ /CaM.…”

“…The Y12E mutation abrogates binding of Ca 2+ /CaM. It does not affect basal PSD‐95 palmitoylation but antagonizes the Ca 2+ ‐induced reduction in PSD‐95 palmitoylation and impairs the release of PSD‐95 from postsynaptic membranes upon Ca 2+ influx (Zhang et al , ).…”

Dendritic Spine Instability in a Mouse Model of CDKL5 Disorder Is Rescued by Insulin-like Growth Factor 1

“…Expression analysis suggested that CDKL5 can be localized in postsynaptic structures (7) where RNA interference and mutation analysis showed that it can regulate dendritic spine density and morphology and modulate excitatory synaptic function (8). The synaptic localization of CDKL5 seems to be regulated by its direct interaction with the palmitoylated form of postsynaptic density protein 95 (PSD-95) (9,10), or by the formation of a complex involving PSD-95 and its interacting protein netrin-G1 ligand (NGL-1), a target of CDKL5 kinase activity (8).…”