FMP Publications

Our publications are recorded in a searchable database since 2010, updates will be added regularly.

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A conformational intermediate in glutamate receptor activation
Lau(*), A. Y., Salazar, H., Blachowicz(*), L., Ghisi, V., Plested, A. J.; Roux(*), B.
Neuron, 79:492-503

Tags: Molecular Neuroscience and Biophysics (Plested)

Abstract: Ionotropic glutamate receptors (iGluRs) transduce the chemical signal of neurotransmitter release into membrane depolarization at excitatory synapses in the brain. The opening of the transmembrane ion channel of these ligand-gated receptors is driven by conformational transitions that are induced by the association of glutamate molecules to the ligand-binding domains (LBDs). Here, we describe the crystal structure of a GluA2 LBD tetramer in a configuration that involves an approximately 30 degrees rotation of the LBD dimers relative to the crystal structure of the full-length receptor. The configuration is stabilized by an engineered disulfide crosslink. Biochemical and electrophysiological studies on full-length receptors incorporating either this crosslink or an engineered metal bridge show that this LBD configuration corresponds to an intermediate state of receptor activation. GluA2 activation therefore involves a combination of both intra-LBD (cleft closure) and inter-LBD dimer conformational transitions. Overall, these results provide a comprehensive structural characterization of an iGluR intermediate state.

State-dependent FRET reports calcium- and voltage-dependent gating-ring motions in BK channels
Miranda(*), P., Contreras(*), J. E., Plested, A. J., Sigworth(*), F. J., Holmgren(*), M.; Giraldez(*), T.
Proc Natl Acad Sci U S A, 110:5217-5222

Tags: Molecular Neuroscience and Biophysics (Plested)

Abstract: Large-conductance voltage- and calcium-dependent potassium channels (BK, "Big K+") are important controllers of cell excitability. In the BK channel, a large C-terminal intracellular region containing a "gating-ring" structure has been proposed to transduce Ca(2+) binding into channel opening. Using patch-clamp fluorometry, we have investigated the calcium and voltage dependence of conformational changes of the gating-ring region of BK channels, while simultaneously monitoring channel conductance. Fluorescence resonance energy transfer (FRET) between fluorescent protein inserts indicates that Ca(2+) binding produces structural changes of the gating ring that are much larger than those predicted by current X-ray crystal structures of isolated gating rings.

In tight junctions, claudins regulate the interactions between occludin, tricellulin and marvelD3, which, inversely, modulate claudin oligomerization
Cording, J., Berg, J., Käding, N., Bellmann, C., Tscheik, C., Westphal(*), J. K., Milatz(*), S., Günzel(*), D., Wolburg(*), H., Piontek, J., Huber(*), O.; Blasig, I. E.
J Cell Sci, 126:554-564

Tags: Molecular and Cell Physiology (Blasig, IE)

Abstract: Tight junctions seal the paracellular cleft of epithelia and endothelia, form vital barriers between tissue compartments and consist of tight-junction-associated marvel proteins (TAMPs) and claudins. The function of TAMPs and the interaction with claudins are not understood. We therefore investigated the binding between the TAMPs occludin, tricellulin, and marvelD3 and their interaction with claudins in living tight-junction-free human embryonic kidney-293 cells. In contrast to claudins and occludin, tricellulin and marvelD3 showed no enrichment at cell-cell contacts indicating lack of homophilic trans-interaction between two opposing cell membranes. However, occludin, marvelD3 and tricellulin exhibited homophilic cis-interactions, along one plasma membrane, as measured by fluorescence resonance energy transfer. MarvelD3 also cis-interacted with occludin and tricellulin heterophilically. Classic claudins, such as claudin-1 to -5 may show cis-oligomerization with TAMPs, whereas the non-classic claudin-11 did not. Claudin-1 and -5 improved enrichment of occludin and tricellulin at cell-cell contacts. The low mobile claudin-1 reduced the membrane mobility of the highly mobile occludin and tricellulin, as studied by fluorescence recovery after photobleaching. Co-transfection of claudin-1 with TAMPs led to changes of the tight junction strand network of this claudin to a more physiological morphology, depicted by freeze-fracture electron microscopy. The results demonstrate multilateral interactions between the tight junction proteins, in which claudins determine the function of TAMPs and vice versa, and provide deeper insights into the tight junction assembly.

Functional properties of cell-free expressed human endothelin A and endothelin B receptors in artificial membrane environments
Proverbio(*), D., Roos(*), C., Beyermann, M., Orban(*), E., Dötsch(*), V.; Bernhard(*), F.
Bba-Biomembranes, 1828:2182-2192

Tags: Peptide Chemistry (Beyermann)

Abstract: The human endothelin receptors are members of the rhodopsin class A of G-protein coupled receptors and key modulators of blood pressure regulation. Their functional in vitro characterization has widely been limited by the availability of high quality samples. We have optimized cell-free expression protocols for the human endothelin A and endothelin B receptors by implementing co-translational association approaches of the synthesized proteins with supplied liposomes or nanodiscs. Efficiency of membrane association and ligand binding properties of the receptors have systematically been studied in correlation to different membrane environments and lipid types. Ligand binding was analyzed by a number of complementary assays including radioassays, surface plasmon resonance and fluorescence measurements. High affinity binding of the peptide ligand ET-I to both endothelin receptors could be obtained with several conditions and the highest Bmax values were measured In association with nanodiscs. We could further obtain the characteristic differential binding pattern of the two endothelin receptors with a panel of selected agonists and antagonists. Two intrinsic properties of the functionally folded endothelin B receptor, the proteolytic processing based on conformational recognition as well as the formation of SDS-resistant complexes with the peptide ligand ET-1, were observed with samples obtained from several cell-free expression conditions. High affinity and specific binding of ligands could furthermore be obtained with non-purified receptor samples in crude cell-free reaction mixtures, thus providing new perspectives for fast in vitro screening applications. (C) 2013 Elsevier B.V. All rights reserved.

Lipophilic prodrugs of a triazole-containing colchicine analogue in liposomes: Biological effects on human tumor cells
Kuznetsova(*), N. R., Svirshchevskaya(*), E. V., Sitnikov(*), N. S., Abodo(*), L., Sutorius(*), H., Zapke, J., Velder(*), J., Thomopoulou(*), P., Oschkinat, H., Prokop(*), A., Schmalz(*), H. G., Fedorov(*), A. Y.; Vodovozova(*), E. L.
Russ J Bioorg Chem+, 39:543-552

Tags: NMR-Supported Structural Biology (Oschkinat)

Abstract: Colchicine site binders-blockers of tubulin polymerization-are potential antimitotic agents for anticancer therapy. To reduce their systemic toxicity and improve biodistribution, encapsulation in nanosized liposomes may be employed. Liposomes present a convenient means for preparation of injectable for-mulations of hydrophobic compounds, however colchicine as such is known to leak through the lipid bilayer. In this study, newly synthesized triazole-containing analogues of colchicine and allocolchicine, and their palmitic and oleic esters (lipophilic prodrugs) were tested for anti-proliferative activity and apoptosis-inducing potential. In contrast to colchicine conjugates, whose activities ranged with those of colchicine, allocolchicine derivatives exhibited drastically lower effects and were discarded. Liposomes of about 100 nm in diameter composed of egg phosphatidylcholine-yeast phosphatidylinositol-palmitic or oleic prodrug, 8: 1: 1, by mol, were prepared by standard extrusion technique and tested in a panel of four human tumor cell lines. Liposome formulations preserved the biological activities of the parent colchicinoid the most towards human epithelial tumor cells. Moreover, liposomal form of the oleoyl bearing colchicinoid inhibited cell proliferation more efficiently than free lipophilic prodrug. Due to substantial loading capacity of the liposomes, the dispersions contain sufficient concentration of the active agent to test wide dose range in experiments on systemic administration to animals.

Oligomerization of Dynamin Superfamily Proteins in Health and Disease
Faelber(*), K., Gao(*), S., Held(*), M., Posor, Y., Haucke, V., Noe(*), F.; Daumke(*), O.
Prog Mol Biol Transl, 117:411-443

Tags: Molecular Pharmacology and Cell Biology (Haucke)

Abstract: Proteins of the dynamin superfamily are mechanochemical GTPases, which mediate nucleotide-dependent membrane remodeling events. The founding member dynamin is recruited to the neck of clathrin-coated endocytic vesicles where it oligomerizes into helical filaments. Nucleotide-hydrolysis-induced conformational changes in the oligomer catalyze scission of the vesicle neck. Here, we review recent insights into structure, function, and oligomerization of dynamin superfamily proteins and their roles in human diseases. We describe in detail the molecular mechanisms how dynamin oligomerizes at membranes and introduce a model how oligomerization is linked to membrane fission. Finally, we discuss molecular mechanisms how mutations in dynamin could lead to the congenital diseases, Centronuclear Myopathy and Charcot-Marie Tooth disease.

Spatiotemporal control of endocytosis by phosphatidylinositol-3,4-bisphosphate
Posor, Y., Eichhorn-Grünig, M., Puchkov, D., Schöneberg(*), J., Ullrich(*), A., Lampe, A., Müller(*), R., Zarbakhsh(*), S., Gulluni(*), F., Hirsch(*), E., Krauss, M., Schultz(*), C., Schmoranzer, J., Noe(*), F.; Haucke, V.
Nature, 499:233-+

Tags: Molecular Pharmacology and Cell Biology (Haucke)

Abstract: Phosphoinositides serve crucial roles in cell physiology, ranging from cell signalling to membrane traffic(1,2). Among the seven eukaryotic phosphoinositides the best studied species is phosphatidylinositol-4,5-bisphosphate (PI(4,5)P-2), which is concentrated at the plasma membrane where, among other functions, it is required for the nucleation of endocytic clathrin-coated pits(3-6). No phosphatidylinositol other than PI(4,5)P-2 has been implicated in clathrin-mediated endocytosis, whereas the subsequent endosomal stages of the endocytic pathway are dominated by phosphatidylinositol-3-phosphates(PI(3)P)(7). How phosphatidylinositol conversion from PI(4,5)P-2-positive endocytic intermediates to PI(3)P-containing endosomes is achieved is unclear. Here we show that formation of phosphatidylinositol-3,4-bisphosphate (PI(3,4)P-2) by class II phosphatidylinositol-3-kinase C2 alpha (PI(3) K C2 alpha) spatiotemporally controls clathrin-mediated endocytosis. Depletion of PI(3,4)P-2 or PI(3)K C2 alpha impairs the maturation of late-stage clathrin-coated pits before fission. Timed formation of PI(3,4)P-2 by PI(3)K C2 alpha is required for selective enrichment of the BAR domain protein SNX9 at late-stage endocytic intermediates. These findings provide a mechanistic framework for the role of PI(3,4)P-2 in endocytosis and unravel a novel discrete function of PI(3,4)P-2 in a central cell physiological process.

PI4K2beta/AP-1-based TGN-endosomal sorting regulates Wnt signaling
Wieffer, M., Cibrian Uhalte(*), E., Posor, Y., Otten(*), C., Branz, K., Schütz, I., Mössinger, J., Schu(*), P., Abdelilah-Seyfried(*), S., Krauss, M.; Haucke, V.
Curr Biol, 23:2185-2190

Tags: Molecular Pharmacology and Cell Biology (Haucke)

Abstract: Endosomal membrane traffic serves crucial roles in cell physiology, signaling, and development. Sorting between endosomes and the trans-Golgi network (TGN) is regulated among other factors by the adaptor AP-1, an essential component of multicellular organisms. Membrane recruitment of AP-1 requires phosphatidylinositol 4-phosphate [PI(4)P], though the precise mechanisms and PI4 kinase isozyme (or isozymes) involved in generation of this PI(4)P pool remain unclear. The Wnt pathway is a major developmental signaling cascade and depends on endosomal sorting in Wnt-sending cells. Whether TGN/endosomal sorting modulates signaling downstream of Frizzled (Fz) receptors in Wnt-receiving cells is unknown. Here, we identify PI4-kinase type 2beta (PI4K2beta) as a regulator of TGN/endosomal sorting and Wnt signaling. PI4K2beta and AP-1 interact directly and are required for efficient sorting between endosomes and the TGN. Zebrafish embryos depleted of PI4K2beta or AP-1 lack pectoral fins due to defective Wnt signaling. Rescue experiments demonstrate requirements for PI4K2beta-AP-1 complex formation and PI4K2beta-mediated PI(4)P synthesis. Furthermore, PI4K2beta binds to the Fz-associated component Dishevelled (Dvl) and regulates endosomal recycling of Fz receptors and Wnt target gene expression. These data reveal an evolutionarily conserved role for PI4K2beta and AP-1 in coupling phosphoinositide metabolism to AP-1-mediated sorting and Wnt signaling.

The Bacterial Translocon SecYEG Opens upon Ribosome Binding
Knyazev(*), D. G., Lents(*), A., Krause, E., Ollinger(*), N., Siligan(*), C., Papinski(*), D., Winter(*), L., Horner(*), A.; Pohl(*), P.
Journal of Biological Chemistry, 288:17941-17946

Tags: Mass Spectrometry (Krause, E.)

Abstract: In co-translational translocation, the ribosome funnel and the channel of the protein translocation complex SecYEG are aligned. For the nascent chain to enter the channel immediately after synthesis, a yet unidentified signal triggers displacement of the SecYEG sealing plug from the pore. Here, we show that ribosome binding to the resting SecYEG channel triggers this conformational transition. The purified and reconstituted SecYEG channel opens to form a large ion-conducting channel, which has the conductivity of the plug deletion mutant. The number of ion-conducting channels inserted into the planar bilayer per fusion event roughly equals the number of SecYEG channels counted by fluorescence correlation spectroscopy in a single proteoliposome. Thus, the open probability of the channel must be close to unity. To prevent the otherwise lethal proton leak, a closed post-translational conformation of the SecYEG complex bound to a ribosome must exist.

Compromised fidelity of endocytic synaptic vesicle protein sorting in the absence of stonin 2
Kononenko, N. L., Diril(*), M. K., Puchkov, D., Kintscher(*), M., Koo(*), S. J., Pfuhl(*), G., Winter(*), Y., Wienisch(*), M., Klingauf(*), J., Breustedt(*), J., Schmitz(*), D., Maritzen, T.; Haucke, V.
Proc Natl Acad Sci U S A, 110:E526-535

Tags: Molecular Pharmacology and Cell Biology (Haucke),Membrane Traffic and Cell Motility (Maritzen)

Abstract: Neurotransmission depends on the exocytic fusion of synaptic vesicles (SVs) and their subsequent reformation either by clathrin-mediated endocytosis or budding from bulk endosomes. How synapses are able to rapidly recycle SVs to maintain SV pool size, yet preserve their compositional identity, is poorly understood. We demonstrate that deletion of the endocytic adaptor stonin 2 (Stn2) in mice compromises the fidelity of SV protein sorting, whereas the apparent speed of SV retrieval is increased. Loss of Stn2 leads to selective missorting of synaptotagmin 1 to the neuronal surface, an elevated SV pool size, and accelerated SV protein endocytosis. The latter phenotype is mimicked by overexpression of endocytosis-defective variants of synaptotagmin 1. Increased speed of SV protein retrieval in the absence of Stn2 correlates with an up-regulation of SV reformation from bulk endosomes. Our results are consistent with a model whereby Stn2 is required to preserve SV protein composition but is dispensable for maintaining the speed of SV recycling.

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Leibniz-Forschungsinstitut für Molekulare Pharmakologie im Forschungsverbund Berlin e.V. (FMP)
Campus Berlin-Buch
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