FMP Publications

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

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References
Real-Time Monitoring of Membrane-Protein Reconstitution by Isothermal Titration Calorimetry
Jahnke, N., Krylova, O. O., Hoomann(*), T., Vargas(*), C., Fiedler(*), S., Pohl(*), P.; Keller(*), S.
Anal Chem, 86:920-927
(2014)

Tags: Biophysics of Membrane Proteins (Keller)

Abstract: Phase diagrams offer a wealth of thermodynamic information on aqueous mixtures of bilayer-forming lipids and micelle-forming detergents, providing a straightforward means of monitoring and adjusting the supramolecular state of such systems. However, equilibrium phase diagrams are of very limited use for the reconstitution of membrane proteins because of the occurrence of irreversible, unproductive processes such as aggregation and precipitation that compete with productive reconstitution. Here, we exemplify this by dissecting the effects of the K+ channel KcsA on the process of bilayer self-assembly in a mixture of Escherichia coli polar lipid extract and the nonionic detergent octyl-beta-D-glucopyranoside. Even at starting concentrations in the low micromolar range, KcsA has a tremendous impact on the supramolecular organization of the system, shifting the critical lipid/detergent ratios at the onset and completion of vesicle formation by more than 2-fold. Thus, equilibrium phase diagrams obtained for protein-free lipid/detergent mixtures would be misleading when used to guide the reconstitution process. To address this issue, we demonstrate that, even under such nonequilibrium conditions, high-sensitivity isothermal titration calorimetry can be exploited to monitor the progress of membrane-protein reconstitution in real time, in a noninvasive manner, and at high resolution to yield functional proteoliposomes with a narrow size distribution for further downstream applications.

Identification of LRRC8 heteromers as an essential component of the volume-regulated anion channel VRAC
Voss, F. K., Ullrich, F., Münch, J., Lazarow, K., Lutter, D., Mah(*), N., Andrade-Navarro(*), M. A., von Kries, J. P., Stauber, T.; Jentsch, T. J.
Science, 344:634-638
(2014)

Tags: Physiology and Pathology of Ion Transport (Jentsch), Screening Unit (von Kries)

Abstract: Regulation of cell volume is critical for many cellular and organismal functions, yet the molecular identity of a key player, the volume-regulated anion channel VRAC, has remained unknown. A genome-wide small interfering RNA screen in mammalian cells identified LRRC8A as a VRAC component. LRRC8A formed heteromers with other LRRC8 multispan membrane proteins. Genomic disruption of LRRC8A ablated VRAC currents. Cells with disruption of all five LRRC8 genes required LRRC8A cotransfection with other LRRC8 isoforms to reconstitute VRAC currents. The isoform combination determined VRAC inactivation kinetics. Taurine flux and regulatory volume decrease also depended on LRRC8 proteins. Our work shows that VRAC defines a class of anion channels, suggests that VRAC is identical to the volume-sensitive organic osmolyte/anion channel VSOAC, and explains the heterogeneity of native VRAC currents.

ClC-7 expression levels critically regulate bone turnover, but not gastric acid secretion
Supanchart(*), C., Wartosch, L., Schlack(*), C., Kühnisch(*), J., Felsenberg, D., Fuhrmann(*), J. C., de Vernejoul(*), M. C., Jentsch, T. J.; Kornak(*), U.
Bone, 58:92-102
(2014)

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Abstract: Mutations in the 2Cl(-)/1H(+)-exchanger ClC-7 impair osteoclast function and cause different types of osteodastrich osteopetrosis. However, it is unknown to what extent ClC-7 function has to be reduced to become rate-limiting for bone resorption. In osteoclasts from osteopetrosis patients expression of the mutated ClC-7 protein did not correlate with disease severity and resorption impairment. Therefore, a series of transgenic mice expressing ClC-7 in osteoclasts at different levels was generated. Crossing of these mice with Clat7(-/-) mutants rescued the osteopetrotic phenotype to variable degrees. One resulting double transgenic line mimicked human autosomal dominant osteopetrosis. The trabecular bone of these mice showed a reduction of osteoblast numbers, osteoid, and osteoblast marker gene expression indicative of reduced osteoblast function. In osteoclasts from these mutants ClC-7 expression levels were 20 to 30% of wildtype levels. These reduced levels not only impaired resorptive activity, but also increased numbers, size and nucleus numbers of osteoclasts differentiated in vitro. Although ClC-7 was expressed in the stomach and PTH levels were high in Clcn7(-/-) mutants loss of ClC-7 did not entail a relevant elevation of gastric pH. In conclusion, we show that in our model a reduction of ClC-7 function by approximately 70% is sufficient to increase bone mass, but does not necessarily enhance bone formation. ClC-7 does not appear to be crucially involved in gastric acid secretion, which explains the absence of an osteopetrorickets phenotype in CLCN7-related osteopetrosis.

Stretch-activation of angiotensin II type 1a receptors contributes to the myogenic response of mouse mesenteric and renal arteries
Schleifenbaum(*), J., Kassmann(*), M., Szijarto(*), I. A., Hercule(*), H. C., Tano(*), J. Y., Weinert, S., Heidenreich, M., Pathan(*), A. R., Anistan(*), Y. M., Alenina(*), N., Rusch(*), N. J., Bader(*), M., Jentsch, T. J.; Gollasch(*), M.
Circ Res, 115:263-272
(2014)

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Abstract: RATIONALE: Vascular wall stretch is the major stimulus for the myogenic response of small arteries to pressure. The molecular mechanisms are elusive, but recent findings suggest that G protein-coupled receptors can elicit a stretch response. OBJECTIVE: To determine whether angiotensin II type 1 receptors (AT1R) in vascular smooth muscle cells exert mechanosensitivity and identify the downstream ion channel mediators of myogenic vasoconstriction. METHODS AND RESULTS: We used mice deficient in AT1R signaling molecules and putative ion channel targets, namely AT1R, angiotensinogen, transient receptor potential channel 6 (TRPC6) channels, or several subtypes of the voltage-gated K+ (Kv7) gene family (KCNQ3, 4, or 5). We identified a mechanosensing mechanism in isolated mesenteric arteries and in the renal circulation that relies on coupling of the AT1R subtype a to a Gq/11 protein as a critical event to accomplish the myogenic response. Arterial mechanoactivation occurs after pharmacological block of AT1R and in the absence of angiotensinogen or TRPC6 channels. Activation of AT1R subtype a by osmotically induced membrane stretch suppresses an XE991-sensitive Kv channel current in patch-clamped vascular smooth muscle cells, and similar concentrations of XE991 enhance mesenteric and renal myogenic tone. Although XE991-sensitive KCNQ3, 4, and 5 channels are expressed in vascular smooth muscle cells, XE991-sensitive K+ current and myogenic contractions persist in arteries deficient in these channels. CONCLUSIONS: Our results provide definitive evidence that myogenic responses of mouse mesenteric and renal arteries rely on ligand-independent, mechanoactivation of AT1R subtype a. The AT1R subtype a signal relies on an ion channel distinct from TRPC6 or KCNQ3, 4, or 5 to enact vascular smooth muscle cell activation and elevated vascular resistance.

A missense mutation accelerating the gating of the lysosomal Cl-/H+-exchanger ClC-7/Ostm1 causes osteopetrosis with gingival hamartomas in cattle
Sartelet(*), A., Stauber, T., Coppieters(*), W., Ludwig, C. F., Fasquelle(*), C., Druet(*), T., Zhang(*), Z. Y., Ahariz(*), N., Cambisano(*), N., Jentsch, T. J.; Charlier(*), C.
Dis Model Mech, 7:119-128
(2014)

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Abstract: Chloride-proton exchange by the lysosomal anion transporter ClC7/Ostm1 is of pivotal importance for the physiology of lysosomes and bone resorption. Mice lacking either ClC-7 or Ostm1 develop a lysosomal storage disease and mutations in either protein have been found to underlie osteopetrosis in mice and humans. Some human disease-causing CLCN7 mutations accelerate the usually slow voltage-dependent gating of ClC-7/Ostm1. However, it has remained unclear whether the fastened kinetics is indeed causative for the disease. Here we identified and characterized a new deleterious ClC-7 mutation in Belgian Blue cattle with a severe symptomatology including perinatal lethality and in most cases gingival hamartomas. By autozygosity mapping and genome-wide sequencing we found a handful of candidate variants, including a cluster of three private SNPs causing the substitution of a conserved tyrosine in the CBS2 domain of ClC-7 by glutamine. The case for ClC-7 was strengthened by subsequent examination of affected calves that revealed severe osteopetrosis. The Y750Q mutation largely preserved the lysosomal localization and assembly of ClC-7/Ostm1, but drastically accelerated its activation by membrane depolarization. These data provide first evidence that accelerated ClC-7/Ostm1 gating per se is deleterious, highlighting a physiological importance of the slow voltage-activation of ClC-7/Ostm1 in lysosomal function and bone resorption.

Disrupting MLC1 and GlialCAM and ClC-2 interactions in leukodystrophy entails glial chloride channel dysfunction
Hoegg-Beiler, M. B., Sirisi(*), S., Orozco, I. J., Ferrer(*), I., Hohensee, S., Auberson, M., Gödde, K., Vilches(*), C., de Heredia(*), M. L., Nunes(*), V., Estevez(*), R.; Jentsch, T. J.
Nat Commun, 5:3475
(2014)

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Abstract: Defects in the astrocytic membrane protein MLC1, the adhesion molecule GlialCAM or the chloride channel ClC-2 underlie human leukoencephalopathies. Whereas GlialCAM binds ClC-2 and MLC1, and modifies ClC-2 currents in vitro, no functional connections between MLC1 and ClC-2 are known. Here we investigate this by generating loss-of-function Glialcam and Mlc1 mouse models manifesting myelin vacuolization. We find that ClC-2 is unnecessary for MLC1 and GlialCAM localization in brain, whereas GlialCAM is important for targeting MLC1 and ClC-2 to specialized glial domains in vivo and for modifying ClC-2's biophysical properties specifically in oligodendrocytes (OLs), the cells chiefly affected by vacuolization. Unexpectedly, MLC1 is crucial for proper localization of GlialCAM and ClC-2, and for changing ClC-2 currents. Our data unmask an unforeseen functional relationship between MLC1 and ClC-2 in vivo, which is probably mediated by GlialCAM, and suggest that ClC-2 participates in the pathogenesis of megalencephalic leukoencephalopathy with subcortical cysts.

CLCN7 and TCIRG1 Mutations Differentially Affect Bone Matrix Mineralization in Osteopetrotic Individuals
Barvencik(*), F., Kurth(*), I., Koehne(*), T., Stauber, T., Zustin(*), J., Tsiakas, K., Ludwig, C. F., Beil(*), F. T., Pestka(*), J. M., Hahn(*), M., Santer(*), R., Supanchart(*), C., Kornak(*9, U., Del Fattore(*), A., Jentsch, T. J., Teti(*), A., Schulz(*), A., Schinke(*), T.; Amling(*), M.
J Bone Miner Res, 29:982-991
(2014)

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Transport activity and presence of ClC-7/Ostm1 complex account for different cellular functions
Weinert, S., Jabs, S., Hohensee, S., Chan(*), W. L., Kornak(*), U.; Jentsch, T. J.
Embo Rep, 15:784-791
(2014)

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Abstract: Loss of the lysosomal ClC-7/Ostm1 2Cl(-)/H(+) exchanger causes lysosomal storage disease and osteopetrosis in humans and additionally changes fur colour in mice. Its conversion into a Cl(-) conductance in Clcn7(unc/unc) mice entails similarly severe lysosomal storage, but less severe osteopetrosis and no change in fur colour. To elucidate the basis for these phenotypical differences, we generated Clcn7(td/td) mice expressing an ion transport-deficient mutant. Their osteopetrosis was as severe as in Clcn7(-/-) mice, suggesting that the electric shunt provided by ClC-7(unc) can partially rescue osteoclast function. The normal coat colour of Clcn7(td/td) mice and their less severe neurodegeneration suggested that the ClC-7 protein, even when lacking measurable ion transport activity, is sufficient for hair pigmentation and that the conductance of ClC-7(unc) is harmful for neurons. Our in vivo structure-function analysis of ClC-7 reveals that both protein-protein interactions and ion transport must be considered in the pathogenesis of ClC-7-related diseases.

Cationic synthetic peptides: assessment of their antimicrobial potency in liquid preserved boar semen
Speck(*), S., Courtiol(*), A., Junkes, C., Dathe, M., Müller(*), K.; Schulze(*), M.
Plos One, 9:e105949
(2014)

Tags: Peptide-Lipid-Interaction/ Peptide Transport (Dathe)

Abstract: Various semen extender formulas are in use to maintain sperm longevity and quality whilst acting against bacterial contamination in liquid sperm preservation. Aminoglycosides are commonly supplemented to aid in the control of bacteria. As bacterial resistance is increasing worldwide, antimicrobial peptides (AMPs) received lively interest as alternatives to overcome multi-drug resistant bacteria. We investigated, whether synthetic cationic AMPs might be a suitable alternative for conventional antibiotics in liquid boar sperm preservation. The antibacterial activity of two cyclic AMPs (c-WWW, c-WFW) and a helical magainin II amide analog (MK5E) was studied in vitro against two Gram-positive and eleven Gram-negative bacteria. Isolates included ATCC reference strains, multi-resistant E. coli and bacteria cultured from boar semen. Using broth microdilution, minimum inhibitory concentrations were determined for all AMPs. All AMPs revealed activity towards the majority of bacteria but not against Proteus spp. (all AMPs) and Staphylococcus aureus ATCC 29213 (MK5E). We could also demonstrate that c-WWW and c-WFW were effective against bacterial growth in liquid preserved boar semen in situ, especially when combined with a small amount of gentamicin. Our results suggest that albeit not offering a complete alternative to traditional antibiotics, the use of AMPs offers a promising solution to decrease the use of conventional antibiotics and thereby limit the selection of multi-resistant strains.

Effects of cationic antimicrobial peptides on liquid-preserved boar spermatozoa
Schulze(*), M., Junkes, C., Mueller(*), P., Speck(*), S., Ruediger(*), K., Dathe, M.; Mueller(*), K.
Plos One, 9:e100490
(2014)

Tags: Peptide-Lipid-Interaction/ Peptide Transport (Dathe)

Abstract: Antibiotics are mandatory additives in semen extenders to control bacterial contamination. The worldwide increase in resistance to conventional antibiotics requires the search for alternatives not only for animal artificial insemination industries, but also for veterinary and human medicine. Cationic antimicrobial peptides are of interest as a novel class of antimicrobial additives for boar semen preservation. The present study investigated effects of two synthetic cyclic hexapeptides (c-WFW, c-WWW) and a synthetic helical magainin II amide derivative (MK5E) on boar sperm during semen storage at 16 degrees C for 4 days. The standard extender, Beltsville Thawing Solution (BTS) containing 250 microg/mL gentamicin (standard), was compared to combinations of BTS with each of the peptides in a split-sample procedure. Examination revealed peptide- and concentration-dependent effects on sperm integrity and motility. Negative effects were more pronounced for MK5E than in hexapeptide-supplemented samples. The cyclic hexapeptides were partly able to stimulate a linear progressive sperm movement. When using low concentrations of cyclic hexapeptides (4 microM c-WFW, 2 microM c-WWW) sperm quality was comparable to the standard extender over the course of preservation. C-WFW-supplemented boar semen resulted in normal fertility rates after AI. In order to investigate the interaction of peptides with the membrane, electron spin resonance spectroscopic measurements were performed using spin-labeled lipids. C-WWW and c-WFW reversibly immobilized an analog of phosphatidylcholine (PC), whereas MK5E caused an irreversible increase of PC mobility. These results suggest testing the antimicrobial efficiency of non-toxic concentrations of selected cyclic hexapeptides as potential candidates to supplement/replace common antibiotics in semen preservation.

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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 
+4930 94793 - 109 (Fax)
info(at)fmp-berlin.de

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