FMP Publications

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

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Domain organization and function in GluK2 subtype kainate receptors
Das(*), U., Kumar(*), J., Mayer(*), M. L.; Plested, A. J.
Proc Natl Acad Sci U S A, 107:8463-8468

Tags: Molecular Neuroscience and Biophysics (Plested)

Abstract: Glutamate receptor ion channels (iGluRs) are excitatory neurotransmitter receptors with a unique molecular architecture in which the extracellular domains assemble as a dimer of dimers. The structure of individual dimer assemblies has been established previously for both the isolated ligand-binding domain (LBD) and more recently for the larger amino terminal domain (ATD). How these dimers pack to form tetrameric assemblies in intact iGluRs has remained controversial. Using recently solved crystal structures for the GluK2 kainate receptor ATD as a guide, we performed cysteine mutant cross-linking experiments in full-length tetrameric GluK2 to establish how the ATD packs in a dimer of dimers assembly. A similar approach, using a full-length AMPA receptor GluA2 crystal structure as a guide, was used to design cysteine mutant cross-links for the GluK2 LBD dimer of dimers assembly. The formation of cross-linked tetramers in full-length GluK2 by combinations of ATD and LBD mutants which individually produce only cross-linked dimers suggests that subunits in the ATD and LBD layers swap dimer partners. Functional studies reveal that cross-linking either the ATD or the LBD inhibits activation of GluK2 and that, in the LBD, cross-links within and between dimers have different effects. These results establish that kainate and AMPA receptors have a conserved extracellular architecture and provide insight into the role of individual dimer assemblies in activation of ion channel gating.

Tricellulin forms homomeric and heteromeric tight junctional complexes
Westphal(*), J. K., Dörfel(*), M. J., Krug(*), S. M., Cording, J. D., Piontek, J., Blasig, I. E., Tauber(*), R., Fromm(*), M.; Huber(*), O.
Cellular and Molecular Life Sciences, 67:2057-2068

Tags: Molecular Cell Physiology (Blasig, I.E.)

Abstract: Sealing of the paracellular cleft by tight junctions is of central importance for epithelia and endothelia to function as efficient barriers between the extracellular space and the inner milieu. Occludin and claudins represent the major tight junction components involved in establishing this barrier function. A special situation emerges at sites where three cells join together. Tricellulin, a recently identified tetraspan protein concentrated at tricellular contacts, was reported to organize tricellular as well as bicellular tight junctions. Here we show that in MDCK cells, the tricellulin C-terminus is important for the basolateral translocation of tricellulin, whereas the N-terminal domain appears to be involved in directing tricellulin to tricellular contacts. In this respect, identification of homomeric tricellulin-tricellulin and of heteromeric tricellulin-occludin complexes extends a previously published model and suggests that tricellulin and occludin are transported together to the edges of elongating bicellular junctions and get separated when tricellular contacts are formed.

On the interaction of Clostridium perfringens enterotoxin with claudins
Veshnyakova, A., Protze, J., Rossa, J., Blasig, I. E., Krause, G.; Piontek, J.
Toxins (Basel), 2:1336-1356

Tags: Molecular Cell Physiology (Blasig, I.E.), Structural Bioinformatics and Protein Design (Krause, G)

Abstract: Clostridium perfringens causes one of the most common foodborne illnesses, which is largely mediated by the Clostridium perfringens enterotoxin (CPE). The toxin consists of two functional domains. The N-terminal region mediates the cytotoxic effect through pore formation in the plasma membrane of the mammalian host cell. The C-terminal region (cCPE) binds to the second extracellular loop of a subset of claudins. Claudin-3 and claudin-4 have been shown to be receptors for CPE with very high affinity. The toxin binds with weak affinity to claudin-1 and -2 but contribution of these weak binding claudins to CPE-mediated disease is questionable. cCPE is not cytotoxic, however, it is a potent modulator of tight junctions. This review describes recent progress in the molecular characterization of the cCPE-claudin interaction using mutagenesis, in vitro binding assays and permeation studies. The results promote the development of recombinant cCPE-proteins and CPE-based peptidomimetics to modulate tight junctions for improved drug delivery or to treat tumors overexpressing claudins.

Participation of the second extracellular loop of claudin-5 in paracellular tightening against ions, small and large molecules
Piehl, C., Piontek, J., Cording, J., Wolburg(*), H.; Blasig, I. E.
Cellular and molecular life sciences : CMLS, 67:2131-2140

Tags: Molecular Cell Physiology (Blasig, I.E.)

Abstract: Tight junctions control paracellular permeability. Here, we analyzed the impact of residues in the second extracellular loop (ECL2) of mouse claudin-5 on paracellular permeability. Stable expression of claudin-5(wild type) in MDCK-II cells-but not that of mutants R145A, Y148A, Y158A or E159Q-increased transepithelial electrical resistance and decreased fluorescein permeation. Expression of claudin-5(Y148A), (Y158A) or (E159Q) enhanced permeability of FITC-dextran(10 kDa), which was unchanged in cells expressing claudin-5(wild type) or claudin-5(R145A). In contrast, targeting to tight junctions, strand morphology and tight junction assembly were unchanged. It is concluded that R145 is unessential for trans-interaction of claudin-5, but necessary for tightening against small solutes and ions. The highly conserved residues Y148, Y158 and E159 in ECL2 of claudin-5 contribute to homo- and/or heterophilic trans-interaction between classic claudins and thereby tighten the paracellular space against ions, small and large molecules. These results provide novel insights into the molecular function of tight junctions.

The Investigation of cis- and trans-Interactions Between Claudins
Haseloff, R. F., Piontek, J.; Blasig, I. E.
Curr Top Membr, 65:97-112

Tags: Molecular Cell Physiology (Blasig, I.E.)

Abstract: OVERVIEW Claudins control the paracellular permeability of the tight junctions in epithelial and endothelial cells forming single cell layers. Several claudins may constitute a network of strands, establishing a continuous barrier within the intercellular clefts of the monolayer. Depending on the claudin composition of a given tissue, the intracellular space may be tight for any solute or permeable for compounds of different molecular weight or differently charged ions. These functions are largely based on intermolecular claudin claudin interactions. Strand formation between claudins requires two components: a longitudinal association along the plasma membrane of the cell-cis-interaction-and an interplay from one cell surface to the next one-trans-interaction. This chapter is aimed at reviewing methods for the analysis of cis- and trans-interacting claudins.

Glycogen synthase kinase 3beta interaction protein functions as an A-kinase anchoring protein
Hundsrucker, C., Skroblin, P., Christian, F., Zenn(*), H. M., Popara, V., Joshi, M., Eichhorst, J., Wiesner, B., Herberg(*), F. W., Reif, B., Rosenthal(*), W.; Klussmann, E.
J Biol Chem, 285:5507-5521

Tags: Anchored Signalling (Klussmann), Solid-State NMR Spectroscopy (Reif), Cellular Imaging (Wiesner)

Abstract: A-kinase anchoring proteins (AKAPs) include a family of scaffolding proteins that target protein kinase A (PKA) and other signaling proteins to cellular compartments and thereby confine the activities of the associated proteins to distinct regions within cells. AKAPs bind PKA directly. The interaction is mediated by the dimerization and docking domain of regulatory subunits of PKA and the PKA-binding domain of AKAPs. Analysis of the interactions between the dimerization and docking domain and various PKA-binding domains yielded a generalized motif allowing the identification of AKAPs. Our bioinformatics and peptide array screening approaches based on this signature motif identified GSKIP (glycogen synthase kinase 3beta interaction protein) as an AKAP. GSKIP directly interacts with PKA and GSK3beta (glycogen synthase kinase 3beta). It is widely expressed and facilitates phosphorylation and thus inactivation of GSK3beta by PKA. GSKIP contains the evolutionarily conserved domain of unknown function 727. We show here that this domain of GSKIP and its vertebrate orthologues binds both PKA and GSK3beta and thereby provides a mechanism for the integration of PKA and GSK3beta signaling pathways.

Modulation of G-protein coupled receptor sample quality by modified cell-free expression protocols: A case study of the human endothelin A receptor
Junge(*), F., Luh(*), L. M., Proverbio(*), D., Schäfer(*), B., Abele(*), R., Beyermann, M., Dötsch(*), V.; Bernhard(*), F.
J Struct Biol, 172:94-106

Tags: Peptide Synthesis (Beyermann)

Abstract: G-protein coupled receptors still represent one of the most challenging targets in membrane protein research. Here we present a strategic approach for the cell-free synthesis of these complex membrane proteins exemplified by the preparative scale production of the human endothelin A receptor. The versatility of the cell-free expression system was used to modulate sample quality by alteration of detergents hence presenting different solubilization environments to the synthesized protein at different stages of the production process. Sample properties after co-translational and post-translational solubilization have been analysed by evaluation of homogeneity, protein stability and receptor ligand binding competence. This is a first quality evaluation of a membrane protein obtained in two different cell-free expression modes and we demonstrate that both can be used for the production of ligand-binding competent endothelin A receptor in quantities sufficient for structural approaches. The presented strategy of cell-free expression protocol development could serve as basic guideline for the production of related receptors in similar systems. (C) 2010 Elsevier Inc. All rights reserved.

Effects of ACE2 inhibition in the post-myocardial infarction heart
Kim(*), M. A., Yang(*), D., Kida(*), K., Molotkova(*), N., Yeo(*), S. J., Varki(*), N., Iwata(*), M., Dalton(*), N. D., Peterson(*), K. L., Siems, W. E., Walther(*), T., Cowling(*), R. T., Kjekshus(*), J.; Greenberg(*), B.
Journal of cardiac failure, 16:777-785

Tags: Biochemical Neurobiology (Siems)

Abstract: BACKGROUND: There is evidence that angiotensin-converting enzyme 2 (ACE2) is cardioprotective. To assess this in the post-myocardial infarction (MI) heart, we treated adult male Sprague-Dawley rats with either placebo (PL) or C16, a selective ACE2 inhibitor, after permanent coronary artery ligation or sham operation. METHODS AND RESULTS: Coronary artery ligation resulting in MI between 25% to 50% of the left ventricular (LV) circumference caused substantial cardiac remodeling. Daily C16 administration from postoperative days 2 to 28 at a dose that inhibited myocardial ACE2 activity was associated with a significant increase in MI size and reduction in LV % fractional shortening. Treatment with C16 did not significantly affect post-MI increases in LV end-diastolic dimension but did inhibit increases in wall thickness and fibrosis in non-infarcted LV. On postoperative day 7, C16 had no significant effect on the increased level of apoptosis in the infarct and border zones nor did it significantly affect capillary density surrounding the MI. It did, however, significantly reduce the number of c-kit(+) cells in the border region. CONCLUSIONS: These findings support the notion that ACE2 exerts cardioprotective effects by preserving jeopardized cardiomyocytes in the border zone. The reduction in hypertrophy and fibrosis with C16, however, suggests that ACE2 activity has diverse effects on post-MI remodeling.

Principles and Determinants of G-Protein Coupling by the Rhodopsin-Like Thyrotropin Receptor
Kleinau, G., Jaeschke(*), H., Worth, C. L., Mueller(*), S., Gonzalez(*), J., Paschke(*), R.; Krause, G.
Plos One, 5

Tags: Structural Bioinformatics and Protein Design (Krause, G.)

Abstract: In this study we wanted to gain insights into selectivity mechanisms between G-protein-coupled receptors (GPCR) and different subtypes of G-proteins. The thyrotropin receptor (TSHR) binds G-proteins promiscuously and activates both Gs (cAMP) and Gq (IP). Our goal was to dissect selectivity patterns for both pathways in the intracellular region of this receptor. We were particularly interested in the participation of poorly investigated receptor parts. We systematically investigated the amino acids of intracellular loop (ICL) 1 and helix 8 using site-directed mutagenesis alongside characterization of cAMP and IP accumulation. This approach was guided by a homology model of activated TSHR in complex with heterotrimeric Gq, using the X-ray structure of opsin with a bound G-protein peptide as a structural template. We provide evidence that ICL1 is significantly involved in G-protein activation and our model suggests potential interactions with subunits G alpha as well as G beta gamma. Several amino acid substitutions impaired both IP and cAMP accumulation. Moreover, we found a few residues in ICL1 (L440, T441, H443) and helix 8 (R687) that are sensitive for Gq but not for Gs activation. Conversely, not even one residue was found that selectively affects cAMP accumulation only. Together with our previous mutagenesis data on ICL2 and ICL3 we provide here the first systematically completed map of potential interfaces between TSHR and heterotrimeric G-protein. The TSHR/Gq-heterotrimer complex is characterized by more selective interactions than the TSHR/Gs complex. In fact the receptor interface for binding Gs is a subset of that for Gq and we postulate that this may be true for other GPCRs coupling these G-proteins. Our findings support that G-protein coupling and preference is dominated by specific structural features at the intracellular region of the activated GPCR but is completed by additional complementary recognition patterns between receptor and G-protein subtypes.

Routes of epithelial water flow: aquaporins versus cotransporters
Mollajew, R., Zocher(*), F., Horner(*), A., Wiesner, B., Klussmann, E.; Pohl, P.
Biophys J, 99:3647-3656

Tags: Anchored Signalling (Klussmann), Cellular Imaging (Wiesner)

Abstract: The routes water takes through membrane barriers is still a matter of debate. Although aquaporins only allow transmembrane water movement along an osmotic gradient, cotransporters are believed to be capable of water transport against the osmotic gradient. Here we show that the renal potassium-chloride-cotransporter (KCC1) does not pump a fixed amount of water molecules per movement of one K(+) and one Cl(-), as was reported for the analogous transporter in the choroid plexus. We monitored water and potassium fluxes through monolayers of primary cultured renal epithelial cells by detecting tiny solute concentration changes in the immediate vicinity of the monolayer. KCC1 extruded K(+) ions in the presence of a transepithelial K(+) gradient, but did not transport water. KCC1 inhibition reduced epithelial osmotic water permeability P(f) by roughly one-third, i.e., the effect of inhibitors was small in resting cells and substantial in hormonal stimulated cells that contained high concentrations of aquaporin-2 in their apical membranes. The furosemide or DIOA (dihydroindenyl-oxy-alkanoic acid)-sensitive water flux was much larger than expected when water passively followed the KCC1-mediated ion flow. The inhibitory effect of these drugs on water flux was reversed by the K(+)-H(+) exchanger nigericin, indicating that KCC1 affects water transport solely by K(+) extrusion. Intracellular K(+) retention conceivably leads to cell swelling, followed by an increased rate of endocytic AQP2 retrieval from the apical membrane.

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Leibniz-Forschungsinstitut für Molekulare Pharmakologie im Forschungsverbund Berlin e.V. (FMP)
Campus Berlin-Buch
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13125 Berlin, Germany
+4930 94793 - 100 
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