␣-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-type glutamate receptors undergo constitutive and ligand-induced internalization that requires dynamin and the clathrin adaptor complex AP-2. We report here that an atypical basic motif within the cytoplasmic tails of AMPA-type glutamate receptors directly associates with 2-adaptin by a mechanism similar to the recognition of the presynaptic vesicle protein synaptotagmin 1 by AP-2. A synaptotagmin 1-derived AP-2 binding peptide competes the interaction of the AMPA receptor subunit GluR2 with AP-2 and increases the number of surface active glutamate receptors in living neurons. Moreover, fusion of the GluR2-derived tail peptide with a synaptotagmin 1 truncation mutant restores clathrin/AP-2-dependent internalization of the chimeric reporter protein. These data suggest that common mechanisms regulate AP-2-dependent internalization of pre-and postsynaptic membrane proteins.endocytosis ͉ postsynaptic ͉ sorting signal ͉ synaptic plasticity F ast neurotransmission at excitatory synapses is mediated by heterotetrameric ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-type glutamate receptors composed of combinations of four subunits (GluR1-4). AMPA receptors interact with different factors including the transmembrane protein stargazin (1), PDZ proteins GRIP1/ABP, SAP97, and PICK1, and NSF (2). Accumulating evidence suggests that rapid changes in functional postsynaptic AMPA receptor numbers are important means of controlling synaptic efficacy (2-5). AMPA receptors undergo constitutive and regulated clathrin-and dynamin-dependent endocytosis via distinct AMPA-or NMDAinduced signaling cascades (reviewed in refs. 2-5). How exactly AMPA receptor cargo is targeted for clathrin-mediated internalization remains an open question. One possibility is that AMPA receptors are recognized by endocytic adaptor proteins such as the clathrin adaptor complex AP-2, a major endocytic protein interaction hub (6-8). NMDA-induced AMPA receptor internalization can be blocked by overexpression of a GluR2 cytoplasmic tail (CT) peptide (pep2r) or by mutating the putative AP-2 binding motif within the GluR2 CT. Infusion of hippocampal CA1 neurons with the putative AP-2-blocking peptide prevents induction of long-term depression (LTD), suggesting that the association of GluR2 with AP-2 may be an important determinant for NMDA-induced LTD (7). Whether AP-2 directly binds to GluR2 CTs and via which of its four subunits is unknown.Here we have identified the molecular determinants responsible for binding of AP-2 to the CTs of AMPA-type glutamate receptors. We demonstrate that the 2 subunit of AP-2 interacts directly and with nanomolar affinity with a basic motif found in CTs of GluR1-3 and the presynaptic vesicle protein synaptotagmin 1. Our data thus suggest that common mechanisms regulate AP-2-dependent internalization of pre-and postsynaptic membrane proteins.

2.the perinuclear compartment, supports a putative recycling function of the compartment.Our data support a model whereby clathrin-mediated cycling of SVPs between the plasma membrane and a perinuclear recycling compartment in neuronal precursor cells might be involved in the biogenesis of a SV precursor organelle that mediates transport of SVPs along the axon to the nascent synapse.Endocytosis in dendrites has been shown to occur at specialized endocytic zones adjacent to the postsynaptic density (Blanpied et al., 2002). Thus endocytosis of postsynaptic receptors requires untethering of synaptic receptors and lateral movement to extrasynaptic sites at the plasma membrane. Work of Borgdorff and Choquet (2002) on lateral movement of AMPARs in the plasma membrane has shown the existence of a highly mobile pool of AMPARs besides an immobile pool presumably synaptic receptor pool. GluR2 is the key subunit that controls NMDA induced internalization of AMPA receptors (Lee et al., 2002; from the plasma membrane. The short GluR2 cytoplasmic tail interacts with various proteins that regulate trafficking of GluR2 during LTD (see fig. 2.6). Thus activity-dependent internalization of AMPA receptors from the postsynaptic plasma membrane during LTD is a tightly regulated process. Regulation includes on the one hand activity dependent phosphorylation of serine or tyrosine residues within the tail and on the other hand involves protein interactions that can also be regulated by phosphorylation.