PubMed Health⌕ Search

Biomedical subjects

Guido Meyer

Publications and source records attributed to Guido Meyer.

8 recordsLinked to original sources
PubMed2006

Novel putative targets of N-ethylmaleimide sensitive fusion protein (NSF) and alpha/beta soluble NSF attachment proteins (SNAPs) include the Pak-binding nucleotide exchange factor betaPIX.

N-ethylmaleimide sensitive fusion protein (NSF) is a chaperone that plays a crucial role in the fusion of vesicles with target membranes. NSF mediates the ATP-consuming dissociation of a core protein complex that assembles during vesicle fusion and it thereby recharges the fusion machinery to perform multiple rounds of fusion. The binding of NSF to the core complex is mediated by co-chaperones named soluble NSF attachment proteins (SNAPs), for which three isoforms (alpha, beta and gamma) are known. Here, we sought to identify novel targets of the NSF-SNAP complex. A yeast two-hybrid screen using the brain specific betaSNAP isoform as bait revealed, as expected, NSF and several isoforms of the SNARE protein syntaxin as interactors. In addition, three isoforms of the reticulon protein family and two isoforms of BNIP3 interacted with betaSNAP. A yeast two-hybrid screen using NSF as bait identified Rab11-FIP3 and the Pak-binding nucleotide exchange factor betaPIX as putative binding partners. betaPIX interacts with recombinant NSF in co-sedimentation assays and the two proteins may be co-immunoprecipitated. A leucine zipper (LZ) motif within the C-terminus of betaPIX mediates binding to NSF; however, this fragment of betaPIX does not exhibit dominant negative effects in a cellular assay. In summary, our results support the evolving view that NSF has numerous targets in addition to conventional SNARE complexes.

Animals↗
PubMed2004

Regulation of synaptic strength and AMPA receptor subunit composition by PICK1.

PICK1 (protein interacting with C kinase-1) regulates the surface expression of the AMPA receptor (AMPAR) GluR2 subunit, however, the functional consequences of this interaction are not well understood. Previous work has suggested that PICK1 promotes the internalization of AMPARs. However, we found that when PICK1 is virally expressed in the CA1 region of hippocampal slices, it causes an increase in AMPAR-mediated EPSC amplitude. This effect is associated with increased AMPAR rectification and sensitivity to polyamine toxin. These effects are blocked by PKC or calcium/calmodulin-dependent protein kinase II inhibitors, indicating that the virally expressed PICK1 signals through an endogenous kinase cascade. In contrast, blockade of interactions with GluR2 at the N-ethylmaleimide-sensitive factor site did not cause a change in subunit composition, suggesting that the effects of PICK1 are not simply a nonspecific consequence of removing AMPARs from the surface. Immunocytochemical and biochemical analyses in dissociated cultured hippocampal neurons show that PICK1 causes a decrease in endogenous GluR2 surface expression but no change in GluR1 surface levels. To address the physiological role of PICK1, we virally expressed C-terminal GluR2 peptides. Blockade of endogenous PICK1 PDZ (postsynaptic density-95/Discs large/zona occludens-1) domain interactions produced opposite effects on synaptic strength and AMPAR rectification to those observed with PICK1 expression. This demonstrates that AMPAR subunit composition is physiologically regulated through a mechanism involving PICK1 PDZ domain interactions. These findings suggest that PICK1 acts to downregulate the GluR2 content of AMPARs at hippocampal CA1 synapses, thereby increasing synaptic strength at resting membrane potentials.

Animals↗
PubMed2004

Synaptic targeting of neuroligin is independent of neurexin and SAP90/PSD95 binding.

Synaptic cell adhesion and synaptogenesis are thought to involve the interaction of neuroligin, a postsynaptic transmembrane protein, with its presynaptic ligand neurexin. Neuroligin also interacts with SAP90/PSD95, a multidomain scaffolding protein thought to recruit proteins to postsynaptic sites. Using expression of GFP-tagged versions of neuroligin in cultured hippocampal neurons, we find that neuroligin is targeted to synapses via intracellular sequences distinct from its SAP90/PSD95 binding site. A neuroligin mutant lacking the intracellular domain fails to target to synapses. These data indicate that postsynaptic targeting of neuroligin does not rely on the scaffolding action of SAP90/PSD95 and is not induced by binding to presynaptic neurexin. Neuroligin is rather targeted to synapses via a postsynaptic mechanism, which may precede and be necessary for subsequent recruitment of neurexin and other neuroligin interactors such as SAP90/PSD95, suggesting a pivotal position for neuroligin in a putative hierarchy of interactions assembling or stabilizing synapses.

Animals↗
PubMed2004

The complexity of PDZ domain-mediated interactions at glutamatergic synapses: a case study on neuroligin.

The postsynaptic specialisation at glutamatergic synapses is composed of a network of proteins located within the membrane and the underlying postsynaptic density. The strong interconnectivity between the protein components is mediated by a limited number of interaction modes. Particularly abundant are PDZ domain-mediated interactions. An obstacle in understanding the fidelity of postsynaptic processes involving PDZ domains is the high degree of overlap with respect to their binding specificities. Focussing on transsynaptic adhesion molecules, we used the yeast two-hybrid system to obtain an overview of the binding specificities of selected C-terminal PDZ binding motifs. Neuroligin, a postsynaptic cell surface protein that spans the synaptic cleft and interacts with beta-neurexin, served as a starting point. Neuroligin binds to the PDZ domain-containing proteins PSD95, SAP102, Chapsyn110, S-SCAM, Magi1 and 3, Shank1 and 3, Pick1, GOPC, SPAR, Semcap3 and PDZ-RGS3. Next, we examined the relationship between neuroligin and synaptic cell adhesion molecules or glutamate receptor subunits with respect to PDZ-mediated interactions. We found a limited overlap in the PDZ-domain binding specificities of neuroligin with those of Sidekick2 and Ephrin-B2. In contrast, Syndecan2 and IgSF4 show no overlap with the PDZ-domain specificity of neuroligin, instead, they bind to GRIP and syntenin. The AMPA receptor subunit GluR2 interacts with Semcap3 and PDZ-RGS3, whereas the kainate receptor subunits GluR5 and GluR6 show weak interactions with PSD95. In summary, we can sketch a complex pattern of overlap in the binding specificities of synaptic cell surface proteins towards PDZ-domain proteins.

Animals↗
PubMed2003

A brain-specific isoform of small glutamine-rich tetratricopeptide repeat-containing protein binds to Hsc70 and the cysteine string protein.

Small glutamine-rich tetratricopeptide repeat-containing protein (SGT) is a ubiquitously expressed cochaperone of heat shock cognate protein of 70 kDa (Hsc70). SGT binds to the C terminus of Hsc70, a site used by several tetratricopeptide repeat-containing binding partners to recruit Hsc70 into complexes of diverse function. We describe here an isoform of SGT with 60% amino acid sequence identity that we name betaSGT. In contrast to the previously published alphaSGT, betaSGT is almost exclusively expressed in brain. Both isoforms of SGT possess similar binding properties toward Hsc70 and cysteine string protein, a synaptic vesicle-associated J-domain-containing protein. In addition, SGTs oligomerize without preferences among isoforms. The distribution of protein binding motifs on SGTs reveals a modular structure. The N-terminal domains mediate oligomerization. Binding to Hsc70 is impaired by mutations of basic residues within the central tetratricopeptide repeat domain of betaSGT, indicating a two-carboxylate clamp as the binding mode. The tetratricopeptide repeats are also necessary for binding to the cysteine string protein. However, this binding mode is distinct from the two-carboxylate clamp that is involved in Hsc70 binding. The C-terminal regions of SGTs might constitute independent protein interaction domains. We conclude that betaSGT is likely to cooperate with alphaSGT as co-chaperone of Hsc70 in the brain. The modular structure of SGTs allows them to recruit client proteins to Hsc70 and to direct the resulting complex toward downstream proteins that take over the respective client proteins.

Amino Acid Motifs↗
PubMed2003

Rapid and differential regulation of AMPA and kainate receptors at hippocampal mossy fibre synapses by PICK1 and GRIP.

We identified four PDZ domain-containing proteins, syntenin, PICK1, GRIP, and PSD95, as interactors with the kainate receptor (KAR) subunits GluR5(2b,) GluR5(2c), and GluR6. Of these, we show that both GRIP and PICK1 interactions are required to maintain KAR-mediated synaptic function at mossy fiber-CA3 synapses. In addition, PKC alpha can phosphorylate ct-GluR5(2b) at residues S880 and S886, and PKC activity is required to maintain KAR-mediated synaptic responses. We propose that PICK1 targets PKC alpha to phosphorylate KARs, causing their stabilization at the synapse by an interaction with GRIP. Importantly, this mechanism is not involved in the constitutive recycling of AMPA receptors since blockade of PDZ interactions can simultaneously increase AMPAR- and decrease KAR-mediated synaptic transmission at the same population of synapses.

Adaptor Proteins, Signal Transducing↗
PubMed2002

The PDZ proteins PICK1, GRIP, and syntenin bind multiple glutamate receptor subtypes. Analysis of PDZ binding motifs.

Using sequence homology searches, yeast two-hybrid assays and glutathione S-transferase (GST)-pull-down approaches we have identified a series of glutamate receptor subunits that interact differentially with the PDZ proteins GRIP, PICK1, and syntenin. GST-pull-down experiments identified more interactions than detected by yeast two-hybrid assays. We report several receptor-protein interactions, strong ones include: (i) GRIP and syntenin with mGluR7a, mGluR4a, and mGluR6; (ii) PICK1 and GRIP with mGluR3; and (iii) syntenin with all forms of GluR1-4 and mGluR7b. We further characterized the novel mGluR7a-GRIP interaction found both in yeast two-hybrid and GST-pull-down assays and observed that mGluR7a localization overlapped with GRIP with in hippocampal neurons. The wide range of targets for PICK1, GRIP, and syntenin suggests they may represent a molecular mechanism that can concentrate and/or regulate a number of different receptors at a common site on a synapse. These data also suggest that the structural determinants involved in PDZ interactions are more complex than originally envisaged.

Adaptor Proteins, Signal Transducing↗