Publications by authors named "Heinrich Heide"

35 Publications

TLR2-Dependent Reversible Oxidation of Connexin 43 at Cys260 Modifies Electrical Coupling After Experimental Myocardial Ischemia/Reperfusion.

J Cardiovasc Transl Res 2019 10 8;12(5):478-487. Epub 2019 Apr 8.

Department of Anaesthesiology, Intensive Care Medicine, and Pain Therapy, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.

We have shown previously that during myocardial ischemia/reperfusion (MI/R), toll-like receptor 2 (TLR2) signaling regulates connexin 43 (Cx43) subcellular localization and function and dampens arrhythmia formation. We aimed to identify sites capable of TLR2-dependent redox modification within Cx43. Post-ischemic TLR2 or wild-type (WT) mouse hearts were analyzed by OxICAT. Cx43 was mutated to exclude redox modification and transfected into HL-1 cardiomyocytes (CM) that were challenged with a TLR2 agonist. We identified Cys260 of Cx43 to be susceptible to reversible oxidation MI/R; TLR2 leads to reduced HO production in post-ischemic isolated mitochondria and subsequently reduced oxidation of Cx43 at Cys260. Cx43 was dephosphorylated in WT, while phosphorylation was preserved in TLR2. Mutation of Cx43 (C260A) and lentiviral transfection in HL-1 CM accelerated pacemaker activity and reduced activity after TLR2 ligand stimulation. We here provide evidence for TLR2-dependent reversible oxidation of Cx43 at Cys260, which led to decreased Cx43 phosphorylation and affected CM pacemaker frequency and intercellular communication.
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http://dx.doi.org/10.1007/s12265-019-09887-0DOI Listing
October 2019

Rab7-a novel redox target that modulates inflammatory pain processing.

Pain 2017 07;158(7):1354-1365

Institute of Pharmacology, College of Pharmacy, Goethe University, Frankfurt am Main, Germany.

Chronic pain is accompanied by production of reactive oxygen species (ROS) in various cells that are important for nociceptive processing. Recent data indicate that ROS can trigger specific redox-dependent signaling processes, but the molecular targets of ROS signaling in the nociceptive system remain largely elusive. Here, we performed a proteome screen for pain-dependent redox regulation using an OxICAT approach, thereby identifying the small GTPase Rab7 as a redox-modified target during inflammatory pain in mice. Prevention of Rab7 oxidation by replacement of the redox-sensing thiols modulates its GTPase activity. Immunofluorescence studies revealed Rab7 expression to be enriched in central terminals of sensory neurons. Knockout mice lacking Rab7 in sensory neurons showed normal responses to noxious thermal and mechanical stimuli; however, their pain behavior during inflammatory pain and in response to ROS donors was reduced. The data suggest that redox-dependent changes in Rab7 activity modulate inflammatory pain sensitivity.
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http://dx.doi.org/10.1097/j.pain.0000000000000920DOI Listing
July 2017

A dynamic periplasmic electron transfer network enables respiratory flexibility beyond a thermodynamic regulatory regime.

ISME J 2015 Aug 30;9(8):1802-11. Epub 2015 Jan 30.

Department of Applied Biology, Institute for Applied Biosciences, Karlsruhe Institute of Technology (CS), Karlsruhe, Germany.

Microorganisms show an astonishing versatility in energy metabolism. They can use a variety of different catabolic electron acceptors, but they use them according to a thermodynamic hierarchy, which is determined by the redox potential of the available electron acceptors. This hierarchy is reflected by a regulatory machinery that leads to the production of respiratory chains in dependence of the availability of the corresponding electron acceptors. In this study, we showed that the γ-proteobacterium Shewanella oneidensis produces several functional electron transfer chains simultaneously. Furthermore, these chains are interconnected, most likely with the aid of c-type cytochromes. The cytochrome pool of a single S. oneidensis cell consists of ca. 700 000 hemes, which are reduced in the absence on an electron acceptor, but can be reoxidized in the presence of a variety of electron acceptors, irrespective of prior growth conditions. The small tetraheme cytochrome (STC) and the soluble heme and flavin containing fumarate reductase FccA have overlapping activity and appear to be important for this electron transfer network. Double deletion mutants showed either delayed growth or no growth with ferric iron, nitrate, dimethyl sulfoxide or fumarate as electron acceptor. We propose that an electron transfer machinery that is produced irrespective of a thermodynamic hierarchy not only enables the organism to quickly release catabolic electrons to a variety of environmental electron acceptors, but also offers a fitness benefit in redox-stratified environments.
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http://dx.doi.org/10.1038/ismej.2014.264DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4511935PMC
August 2015

Autophagy-dependent PELI3 degradation inhibits proinflammatory IL1B expression.

Autophagy 2014 30;10(11):1937-52. Epub 2014 Oct 30.

a Institute of Biochemistry I-Pathobiochemistry; Goethe University Frankfurt; Faculty of Medicine ; Frankfurt , Germany.

Lipopolysaccharide (LPS)-induced activation of TLR4 (toll-like receptor 4) is followed by a subsequent overwhelming inflammatory response, a hallmark of the first phase of sepsis. Therefore, counteracting excessive innate immunity by autophagy is important to contribute to the termination of inflammation. However, the exact molecular details of this interplay are only poorly understood. Here, we show that PELI3/Pellino3 (pellino E3 ubiquitin protein ligase family member 3), which is an E3 ubiquitin ligase and scaffold protein in TLR4-signaling, is impacted by autophagy in macrophages (MΦ) after LPS stimulation. We noticed an attenuated mRNA expression of proinflammatory Il1b (interleukin 1, β) in Peli3 knockdown murine MΦ in response to LPS treatment. The autophagy adaptor protein SQSTM1/p62 (sequestosome 1) emerged as a potential PELI3 binding partner in TLR4-signaling. siRNA targeting Sqstm1 and Atg7 (autophagy related 7), pharmacological inhibition of autophagy by wortmannin as well as blocking the lysosomal vacuolar-type H(+)-ATPase by bafilomycin A1 augmented PELI3 protein levels, while inhibition of the proteasome had no effect. Consistently, treatment to induce autophagy by MTOR (mechanistic target of rapamycin (serine/threonine kinase)) inhibition or starvation enhanced PELI3 degradation and reduced proinflammatory Il1b expression. PELI3 was found to be ubiquitinated upon LPS stimulation and point mutation of PELI3-lysine residue 316 (Lys316Arg) attenuated Torin2-dependent degradation of PELI3. Immunofluorescence analysis revealed that PELI3 colocalized with the typical autophagy markers MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3 β) and LAMP2 (lysosomal-associated membrane protein 2). Our observations suggest that autophagy causes PELI3 degradation during TLR4-signaling, thereby impairing the hyperinflammatory phase during sepsis.
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http://dx.doi.org/10.4161/auto.32178DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4502728PMC
September 2015

Generator-specific targets of mitochondrial reactive oxygen species.

Free Radic Biol Med 2015 Jan 29;78:1-10. Epub 2014 Oct 29.

Molecular Bioenergetics Group, Goethe-University, D-60590 Frankfurt am Main, Germany; Clinic of Anaesthesiology, Intensive Care Medicine and Pain Therapy, Goethe-University Hospital, Frankfurt am Main, Germany. Electronic address:

To understand the role of reactive oxygen species (ROS) in oxidative stress and redox signaling it is necessary to link their site of generation to the oxidative modification of specific targets. Here we have studied the selective modification of protein thiols by mitochondrial ROS that have been implicated as deleterious agents in a number of degenerative diseases and in the process of biological aging, but also as important players in cellular signal transduction. We hypothesized that this bipartite role might be based on different generator sites for "signaling" and "damaging" ROS and a directed release into different mitochondrial compartments. Because two main mitochondrial ROS generators, complex I (NADH:ubiquinone oxidoreductase) and complex III (ubiquinol:cytochrome c oxidoreductase; cytochrome bc1 complex), are known to predominantly release superoxide and the derived hydrogen peroxide (H2O2) into the mitochondrial matrix and the intermembrane space, respectively, we investigated whether these ROS generators selectively oxidize specific protein thiols. We used redox fluorescence difference gel electrophoresis analysis to identify redox-sensitive targets in the mitochondrial proteome of intact rat heart mitochondria. We observed that the modified target proteins were distinctly different when complex I or complex III was employed as the source of ROS. These proteins are potential targets involved in mitochondrial redox signaling and may serve as biomarkers to study the generator-dependent dual role of mitochondrial ROS in redox signaling and oxidative stress.
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http://dx.doi.org/10.1016/j.freeradbiomed.2014.10.511DOI Listing
January 2015

NOVA: a software to analyze complexome profiling data.

Bioinformatics 2015 Feb 9;31(3):440-1. Epub 2014 Oct 9.

Molecular Bioinformatics Group, Institute of Computer Science, Faculty of Computer Science and Mathematics, Cluster of Excellence Frankfurt "Macromolecular Complexes", Goethe-University, Robert-Mayer-Str. 11-15, 60325 Frankfurt am Main, Germany, Molecular Bioenergetics Group, Medical School, Cluster of Excellence Frankfurt "Macromolecular Complexes", Goethe-University, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany, Functional Proteomics, SFB815 core unit, Medical School, Goethe-University, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany and Nijmegen Centre for Mitochondrial Disorders, Radboud University Medical Centre, 6525 GA, Nijmegen, The Netherlands.

Summary: We introduce nova, a software for the analysis of complexome profiling data. nova supports the investigation of the composition of complexes, cluster analysis of the experimental data, visual inspection and comparison of experiments and many other features.

Availability And Implementation: nova is licensed under the Artistic License 2.0. It is freely available at http://www.bioinformatik.uni-frankfurt.de. nova requires at least Java 7 and runs under Linux, Microsoft Windows and Mac OS.

Contact: [email protected]
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http://dx.doi.org/10.1093/bioinformatics/btu623DOI Listing
February 2015

SYNCRIP-dependent Nox2 mRNA destabilization impairs ROS formation in M2-polarized macrophages.

Antioxid Redox Signal 2014 Dec 29;21(18):2483-97. Epub 2014 Jul 29.

1 Faculty of Medicine, Institute of Biochemistry I-Pathobiochemistry, Goethe-University Frankfurt , Frankfurt, Germany .

Aims: During sepsis, macrophages are alternatively activated toward an M2-like phenotype on contact with apoptotic cells (ACs) or their secretion products. Simultaneously, NADPH oxidase-dependent reactive oxygen species (ROS) formation is attenuated, thus contributing to immune paralysis. However, the exact mechanism remains elusive. Here, we provide mechanistic insights into diminished mRNA stability of the NADPH oxidase Nox2 on macrophage M2 polarization and therefore reduced ROS formation in sepsis.

Results: Murine J774A.1 macrophages were stimulated with conditioned medium (CM) of apoptotic T cells, which reduced Nox2 mRNA and protein expression, consequently decreasing ROS production. An mRNA pulldown approach coupled to mass spectrometry analysis identified the RNA-binding protein SYNCRIP attached to the Nox2 mRNA 3' untranslated region (3'UTR). The binding of SYNCRIP to the 3'UTR of Nox2 mRNA is attenuated after treatment with CM of apoptotic T cells, followed by Nox2 mRNA destabilization. In in vivo models of polymicrobial sepsis such as cecal ligation and puncture, SYNCRIP was strongly downregulated, which was associated with a decreased Nox2 expression in peritoneal macrophages.

Innovation: Downregulation of SYNCRIP in macrophages after contact to material of ACs destabilized Nox2 mRNA and impaired ROS formation, thereby contributing to an M2 phenotype shift of macrophages in sepsis.

Conclusion: M2 polarization of macrophages in sepsis results in an attenuated SYNCRIP binding to the 3'UTR of Nox2 mRNA, destabilizing Nox2 mRNA abundance and expression. Consequently, ROS formation needed to fight against recurrent infections is impaired. In conclusion, SYNCRIP-regulated Nox2 mRNA degradation mediates the hypoinflammatory phase of sepsis.
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http://dx.doi.org/10.1089/ars.2013.5760DOI Listing
December 2014

The LYR protein subunit NB4M/NDUFA6 of mitochondrial complex I anchors an acyl carrier protein and is essential for catalytic activity.

Proc Natl Acad Sci U S A 2014 Apr 24;111(14):5207-12. Epub 2014 Mar 24.

Institute of Biochemistry II, Structural Bioenergetics Group, Medical School, Goethe University Frankfurt, 60438 Frankfurt, Germany.

Mitochondrial complex I is the largest and most complicated enzyme of the oxidative phosphorylation system. It comprises a number of so-called accessory subunits of largely unknown structure and function. Here we studied subunit NB4M [NDUFA6, LYR motif containing protein 6 (LYRM6)], a member of the LYRM family of proteins. Chromosomal deletion of the corresponding gene in the yeast Yarrowia lipolytica caused concomitant loss of the mitochondrial acyl carrier protein subunit ACPM1 from the enzyme complex and paralyzed ubiquinone reductase activity. Exchanging the LYR motif and an associated conserved phenylalanine by alanines in subunit NB4M also abolished the activity and binding of subunit ACPM1. We show, by single-particle electron microscopy and structural modeling, that subunits NB4M and ACPM1 form a subdomain that protrudes from the peripheral arm in the vicinity of central subunit domains known to be involved in controlling the catalytic activity of complex I.
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http://dx.doi.org/10.1073/pnas.1322438111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3986132PMC
April 2014

ND3, ND1 and 39kDa subunits are more exposed in the de-active form of bovine mitochondrial complex I.

Biochim Biophys Acta 2014 Jun 21;1837(6):929-39. Epub 2014 Feb 21.

Queen's University Belfast, School of Biological Sciences, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK. Electronic address:

An intriguing feature of mitochondrial complex I from several species is the so-called A/D transition, whereby the idle enzyme spontaneously converts from the active (A) form to the de-active (D) form. The A/D transition plays an important role in tissue response to the lack of oxygen and hypoxic deactivation of the enzyme is one of the key regulatory events that occur in mitochondria during ischaemia. We demonstrate for the first time that the A/D conformational change of complex I does not affect the macromolecular organisation of supercomplexes in vitro as revealed by two types of native electrophoresis. Cysteine 39 of the mitochondrially-encoded ND3 subunit is known to become exposed upon de-activation. Here we show that even if complex I is a constituent of the I+III2+IV (S1) supercomplex, cysteine 39 is accessible for chemical modification in only the D-form. Using lysine-specific fluorescent labelling and a DIGE-like approach we further identified two new subunits involved in structural rearrangements during the A/D transition: ND1 (MT-ND1) and 39kDa (NDUFA9). These results clearly show that structural rearrangements during de-activation of complex I include several subunits located at the junction between hydrophilic and hydrophobic domains, in the region of the quinone binding site. De-activation of mitochondrial complex I results in concerted structural rearrangement of membrane subunits which leads to the disruption of the sealed quinone chamber required for catalytic turnover.
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http://dx.doi.org/10.1016/j.bbabio.2014.02.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4331043PMC
June 2014

Electrophilic fatty acid species inhibit 5-lipoxygenase and attenuate sepsis-induced pulmonary inflammation.

Antioxid Redox Signal 2014 Jun 3;20(17):2667-80. Epub 2014 Feb 3.

1 Institute for Vascular Signalling, Centre for Molecular Medicine, Goethe University , Frankfurt am Main, Germany .

Aims: The reaction of nitric oxide and nitrite-derived species with polyunsaturated fatty acids yields electrophilic fatty acid nitroalkene derivatives (NO2-FA), which display anti-inflammatory properties. Given that the 5-lipoxygenase (5-LO, ALOX5) possesses critical nucleophilic amino acids, which are potentially sensitive to electrophilic modifications, we determined the consequences of NO2-FA on 5-LO activity in vitro and on 5-LO-mediated inflammation in vivo.

Results: Stimulation of human polymorphonuclear leukocytes (PMNL) with nitro-oleic (NO2-OA) or nitro-linoleic acid (NO2-LA) (but not the parent lipids) resulted in the concentration-dependent and irreversible inhibition of 5-LO activity. Similar effects were observed in cell lysates and using the recombinant human protein, indicating a direct reaction with 5-LO. NO2-FAs did not affect the activity of the platelet-type 12-LO (ALOX12) or 15-LO-1 (ALOX15) in intact cells or the recombinant protein. The NO2-FA-induced inhibition of 5-LO was attributed to the alkylation of Cys418, and the exchange of Cys418 to serine rendered 5-LO insensitive to NO2-FA. In vivo, the systemic administration of NO2-OA to mice decreased neutrophil and monocyte mobilization in response to lipopolysaccharide (LPS), attenuated the formation of the 5-LO product 5-hydroxyeicosatetraenoic acid (5-HETE), and inhibited lung injury. The administration of NO2-OA to 5-LO knockout mice had no effect on LPS-induced neutrophil or monocyte mobilization as well as on lung injury.

Innovation: Prophylactic administration of NO2-OA to septic mice inhibits inflammation and promotes its resolution by interfering in 5-LO-mediated inflammatory processes.

Conclusion: NO2-FAs directly and irreversibly inhibit 5-LO and attenuate downstream acute inflammatory responses.
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http://dx.doi.org/10.1089/ars.2013.5473DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4026401PMC
June 2014

Chronic hypoxia alters mitochondrial composition in human macrophages.

Biochim Biophys Acta 2013 Dec 16;1834(12):2750-60. Epub 2013 Oct 16.

Institute of Biochemistry I/ZAFES, Goethe-University Frankfurt, 60590 Frankfurt, Germany.

Hypoxia inducible factors (HIFs) are important mediators of the cellular adaptive response during acute hypoxia. The role of HIF-1 and HIF-2 during prolonged periods of hypoxia, i.e. chronic hypoxia is less defined. Therefore, we used human THP-1 macrophages with a knockdown of either HIF-1α, HIF-2α, or both HIFα-subunits, incubated them for several days under hypoxia (1% O2), and analyzed responses to hypoxia using 2D-DIGE coupled to MS/MS-analysis. Chronic hypoxia was defined as a time point when the early but transient accumulation of HIFα-subunits and mRNA expression of classical HIF target genes returned towards basal levels, with a new steady state that was constant from 72h onwards. From roughly 800 spots, that were regulated comparing normoxia to chronic hypoxia, about 100 proteins were unambiguously assigned during MS/MS-analysis. Interestingly, a number of glycolytic proteins were up-regulated, while a number of inner mitochondrial membrane proteins were down-regulated independently of HIF-1α or HIF-2α. Chronic hypoxic conditions depleted the mitochondrial mass by autophagy, which occurred independently of HIF proteins. Macrophages tolerate periods of chronic hypoxia very well and adaptive responses occur, at least in part, independently of HIF-1α and/or HIF-2α and comprise mitophagy as a pathway of particular importance.
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http://dx.doi.org/10.1016/j.bbapap.2013.09.023DOI Listing
December 2013

Endo-PDI is required for TNFα-induced angiogenesis.

Free Radic Biol Med 2013 Dec 5;65:1398-1407. Epub 2013 Oct 5.

Institut für Kardiovaskuläre Physiologie, Goethe-Universität, 60590 Frankfurt am Main, Germany. Electronic address:

Protein disulfide isomerase (PDI) and its homologs are oxidoreductases facilitating protein folding in the ER. Endo-PDI (also termed ERp46) is highly expressed in endothelial cells. It belongs to the PDI family but its physiological function is largely unknown. We studied the role of Endo-PDI in endothelial angiogenic responses. Stimulation of human umbilical vein endothelial cells (with TNFα (10ng/ml) increased ERK1/2 phosphorylation. This effect was largely attenuated by Endo-PDI siRNA, whereas JNK and p38 MAP kinase phosphorylation was Endo-PDI independent. Similarly, TNFα-stimulated NF-κB signaling determined by IκBα degradation as well as TNFα-induced ICAM expression was unaffected by Endo-PDI siRNA. The action of Endo-PDI was not mediated by extracellular thiol exchange or cell surface PDI as demonstrated by nonpermeative inhibitors and PDI-neutralizing antibody. Moreover, exogenously added PDI failed to restore ERK1/2 activation after Endo-PDI knockdown. This suggests that Endo-PDI acts intracellularly potentially by maintaining the Ras/Raf/MEK/ERK pathway. Indeed, knockdown of Endo-PDI attenuated Ras activation measured by G-LISA and Raf phosphorylation. ERK activation influences gene expression by the transcriptional factor AP-1, which controls MMP-9 and cathepsin B, two proteases required for angiogenesis. TNFα-stimulated MMP-9 and cathepsin B induction was reduced by silencing of Endo-PDI. Accordingly, inhibition of cathepsin B or Endo-PDI siRNA blocked the TNFα-stimulated angiogenic response in the spheroid outgrowth assays. Moreover ex vivo tube formation and in vivo Matrigel angiogenesis in response to TNFα were attenuated by Endo-PDI siRNA. In conclusion, our study establishes Endo-PDI as a novel, important mediator of AP-1-driven gene expression and endothelial angiogenic function.
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http://dx.doi.org/10.1016/j.freeradbiomed.2013.09.028DOI Listing
December 2013

Methods to analyse composition and dynamics of macromolecular complexes.

Biochem Soc Trans 2013 Oct;41(5):1235-41

*Functional Proteomics, SFB815 Core Unit, Faculty of Medicine, Goethe-University, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany.

Macromolecular complexes are involved in a broad spectrum of cellular processes including protein biosynthesis, protein secretion and degradation, metabolism, DNA replication and repair, and signal transduction along with other important biological processes. The analysis of protein complexes in health and disease is important to gain insights into cellular physiology and pathophysiology. In the last few decades, research has focused on the identification and the dynamics of macromolecular complexes. Several techniques have been developed to isolate native protein complexes from cells and tissues to allow further characterization by microscopic and proteomic analysis. In the present paper, we provide a brief overview of proteomic methods that can be used to identify protein-protein interactions, focusing on recent developments to study the entire complexome of a biological sample.
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http://dx.doi.org/10.1042/BST20130153DOI Listing
October 2013

MicroRNA-223 antagonizes angiogenesis by targeting β1 integrin and preventing growth factor signaling in endothelial cells.

Circ Res 2013 Dec 17;113(12):1320-30. Epub 2013 Sep 17.

From the Institute for Vascular Signalling, Centre for Molecular Medicine, Goethe University and DZHK (German Centre for Cardiovascular Research) partner site Rhine-Main, Frankfurt, Germany (L.S., B.F., N.Z., T.F., J.H., A.E., R.P., I.F.); and Functional Proteomics, SFB 815 Core Unit, Faculty of Medicine, Goethe University, Frankfurt am Main, Germany (H.H.).

Rationale: Endothelial cells in situ are largely quiescent, and their isolation and culture are associated with the switch to a proliferative phenotype.

Objective: To identify antiangiogenic microRNAs expressed by native endothelial cells that are altered after isolation and culture, as well as the protein targets that regulate responses to growth factors.

Methods And Results: Profiling studies revealed that miR-223 was highly expressed in freshly isolated human, murine, and porcine endothelial cells, but those levels decreased in culture. In primary cultures of endothelial cells, vascular endothelial cell growth factor and basic fibroblast growth factor further decreased miR-223 expression. The overexpression of precursor-miR-223 did not affect basal endothelial cell proliferation but abrogated vascular endothelial cell growth factor-induced and basic fibroblast growth factor-induced proliferation, as well as migration and sprouting. Inhibition of miR-223 in vivo using specific antagomirs potentiated postnatal retinal angiogenesis in wild-type mice, whereas recovery of perfusion after femoral artery ligation and endothelial sprouting from aortic rings from adult miR-223(-/y) animals were enhanced. MiR-223 overexpression had no effect on the growth factor-induced activation of ERK1/2 but inhibited the vascular endothelial cell growth factor-induced and basic fibroblast growth factor-induced phosphorylation of their receptors and activation of Akt. β1 integrin was identified as a target of miR-223 and its downregulation reproduced the defects in growth factor receptor phosphorylation and Akt signaling seen after miR-223 overexpression. Reintroduction of β1 integrin into miR-223-ovexpressing cells was sufficient to rescue growth factor signaling and angiogenesis.

Conclusions: These results indicate that miR-223 is an antiangiogenic microRNA that prevents endothelial cell proliferation at least partly by targeting β1 integrin.
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http://dx.doi.org/10.1161/CIRCRESAHA.113.301824DOI Listing
December 2013

5-Lipoxygenase contributes to PPARγ activation in macrophages in response to apoptotic cells.

Cell Signal 2013 Dec 13;25(12):2762-8. Epub 2013 Sep 13.

Institute of Biochemistry I-Pathobiochemistry, Faculty of Medicine, Goethe-University Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt, Germany. Electronic address:

Macrophage polarization to an anti-inflammatory phenotype upon contact with apoptotic cells is a contributing hallmark to immune suppression during the late phase of sepsis. Although the peroxisome proliferator-activated receptor γ (PPARγ) supports this macrophage phenotype switch, it remains elusive how apoptotic cells activate PPARγ. Assuming that a molecule causing PPARγ activation in macrophages originates in the cell membrane of apoptotic cells we analyzed lipid rafts from apoptotic, necrotic, and living human Jurkat T cells which showed the presence of 5-lipoxygenase (5-LO) in lipid rafts of apoptotic cells only. Incubating macrophages with lipid rafts of apoptotic, but not necrotic or living cells, induced PPAR responsive element (PPRE)-driven mRuby reporter gene expression in RAW 264.7 macrophages stably transduced with a 4xPPRE containing vector. Experiments with lipid rafts of apoptotic murine EL4 T cells revealed similar results. To verify the involvement of 5-LO in activating PPARγ in macrophages, Jurkat T cells were incubated with the 5-LO inhibitor MK-866 prior to induction of apoptosis, which failed to induce mRuby expression. Similar results were obtained with lipid rafts of apoptotic EL4 T cells preexposed to the 5-LO inhibitors zileuton and CJ-13610. Interestingly, Jurkat T cells overexpressing 5-LO failed to activate PPARγ in macrophages, while their 5-LO overexpressing apoptotic counterparts did. Our results suggest that during apoptosis 5-LO gets associated with lipid rafts and synthesizes ligands that in turn stimulate PPARγ in macrophages.
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http://dx.doi.org/10.1016/j.cellsig.2013.08.045DOI Listing
December 2013

Age-related changes in the mitochondrial proteome of the fungus Podospora anserina analyzed by 2D-DIGE and LC-MS/MS.

J Proteomics 2013 Oct 19;91:358-74. Epub 2013 Jul 19.

Molecular Bioenergetics Group, Medical School, Cluster of Excellence Frankfurt Macromolecular Complexes, Centre for Membrane Proteomics, Johann Wolfgang Goethe University, 60590 Frankfurt am Main, Germany.

Unlabelled: Many questions concerning the molecular processes during biological aging remain unanswered. Since mitochondria are central players in aging, we applied quantitative two-dimensional difference gel electrophoresis (2D-DIGE) coupled to protein identification by mass spectrometry to study the age-dependent changes in the mitochondrial proteome of the fungus Podospora anserina - a well-established aging model. 67 gel spots exhibited significant, but remarkably moderate intensity changes. While typically the observed changes in protein abundance occurred progressively with age, for several proteins a pronounced change was observed at late age, sometimes inverting the trend observed at younger age. The identified proteins were assigned to a wide range of metabolic pathways including several implicated previously in biological aging. An overall decrease for subunits of complexes I and V of oxidative phosphorylation was confirmed by Western blot analysis and blue-native electrophoresis. Changes in several groups of proteins suggested a general increase in protein biosynthesis possibly reflecting a compensatory mechanism for increased quality control-related protein degradation at later age. Age-related augmentation in abundance of proteins involved in biosynthesis, folding, and protein degradation pathways sustain these observations. Furthermore, a significant decrease of two enzymes involved in the degradation of γ-aminobutyrate (GABA) supported its previously suggested involvement in biological aging.

Biological Significance: We have followed the time course of changes in protein abundance during aging of the fungus P. anserina. The observed moderate but significant changes provide insight into the molecular adaptations to biological aging and highlight the metabolic pathways involved, thereby offering new leads for future research.
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http://dx.doi.org/10.1016/j.jprot.2013.07.008DOI Listing
October 2013

APOOL is a cardiolipin-binding constituent of the Mitofilin/MINOS protein complex determining cristae morphology in mammalian mitochondria.

PLoS One 2013 21;8(5):e63683. Epub 2013 May 21.

Mitochondrial Biology, Buchmann Institute for Molecular Life Sciences, Goethe University, Frankfurt am Main, Germany.

Mitochondrial cristae morphology is highly variable and altered under numerous pathological conditions. The protein complexes involved are largely unknown or only insufficiently characterized. Using complexome profiling we identified apolipoprotein O (APOO) and apolipoprotein O-like protein (APOOL) as putative components of the Mitofilin/MINOS protein complex which was recently implicated in determining cristae morphology. We show that APOOL is a mitochondrial membrane protein facing the intermembrane space. It specifically binds to cardiolipin in vitro but not to the precursor lipid phosphatidylglycerol. Overexpression of APOOL led to fragmentation of mitochondria, a reduced basal oxygen consumption rate, and altered cristae morphology. Downregulation of APOOL impaired mitochondrial respiration and caused major alterations in cristae morphology. We further show that APOOL physically interacts with several subunits of the MINOS complex, namely Mitofilin, MINOS1, and SAMM50. We conclude that APOOL is a cardiolipin-binding component of the Mitofilin/MINOS protein complex determining cristae morphology in mammalian mitochondria. Our findings further assign an intracellular role to a member of the apolipoprotein family in mammals.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0063683PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3660581PMC
December 2013

Conformation-specific crosslinking of mitochondrial complex I.

FEBS Lett 2013 Apr 27;587(7):867-72. Epub 2013 Feb 27.

Queen's University Belfast, School of Biological Sciences, Medical Biology Centre, Belfast, UK.

Complex I is the only component of the eukaryotic respiratory chain of which no high-resolution structure is yet available. A notable feature of mitochondrial complex I is the so-called active/de-active conformational transition of the idle enzyme from the active (A) to the de-active, (D) form. Using an amine- and sulfhydryl-reactive crosslinker of 6.8Å length (SPDP) we found that in the D-form of complex I the ND3 subunit crosslinked to the 39 kDa (NDUFA9) subunit. These proteins could not be crosslinked in the A-form. Most likely, both subunits are closely located in the critical junction region connecting the peripheral hydrophilic domain to the membrane arm of the enzyme where the entrance path for substrate ubiquinone is and where energy transduction takes place.
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http://dx.doi.org/10.1016/j.febslet.2013.02.039DOI Listing
April 2013

The polarity protein Scrib is essential for directed endothelial cell migration.

Circ Res 2013 Mar 29;112(6):924-34. Epub 2013 Jan 29.

Institut für Kardiovaskuläre Physiologie, Goethe-Universität, Theodor-Stern-Kai 7, Frankfurt am Main, Germany.

Rationale: Polarity proteins are involved in the apico-basal orientation of epithelial cells, but relatively little is known regarding their function in mesenchymal cells.

Objective: We hypothesized that polarity proteins also contribute to endothelial processes like angiogenesis.

Methods And Results: Screening of endothelial cells revealed high expression of the polarity protein Scribble (Scrib). On fibronectin-coated carriers Scrib siRNA (siScrib) blocked directed but not random migration of human umbilical vein endothelial cells and led to an increased number and disturbed orientation of cellular lamellipodia. Coimmunoprecipitation/mass spectrometry and glutathione S-transferase (GST) pulldown assays identified integrin α5 as a novel Scrib interacting protein. By total internal reflection fluorescence (TIRF) microscopy, Scrib and integrin α5 colocalize at the basal plasma membrane of endothelial cells. Western blot and fluorescence activated cell sorting (FACS) analysis revealed that silencing of Scrib reduced the protein amount and surface expression of integrin α5 whereas surface expression of integrin αV was unaffected. Moreover, in contrast to fibronectin, the ligand of integrin α5, directional migration on collagen mediated by collagen-binding integrins was unaffected by siScrib. Mechanistically, Scrib supported integrin α5 recycling and protein stability by blocking its interaction with Rab7a, its translocation into lysosomes, and its subsequent degradation by pepstatin-sensitive proteases. In siScrib-treated cells, reinduction of the wild-type protein but not of PSD95, Dlg, ZO-1 (PDZ), or leucine rich repeat domain mutants restored integrin α5 abundance and directional cell migration. The downregulation of Scrib function in Tg(kdrl:EGFP)(s843) transgenic zebrafish embryos delayed the angiogenesis of intersegmental vessels.

Conclusions: Scrib is a novel regulator of integrin α5 turnover and sorting, which is required for oriented cell migration and sprouting angiogenesis.
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http://dx.doi.org/10.1161/CIRCRESAHA.112.300592DOI Listing
March 2013

Identification of α2β1 integrin inhibitor VP-i with anti-platelet properties in the venom of Vipera palaestinae.

Toxicon 2013 Mar 11;64:96-105. Epub 2013 Jan 11.

Center for Molecular Medicine, Department of Vascular Matrix Biology, Frankfurt University Hospital, Excellence Cluster Cardio-Pulmonary System, Theodor-Stern-Kai 7, 60590 Frankfurt, Germany.

Integrins are receptors of the extracellular matrix (ECM), playing a vital role in pathophysiological processes. They bind to ECM ligands like collagens and can mediate wound healing as well as tumor metastasis and thrombosis, thus being a part of cell adhesion and migration as well as platelet aggregation. For this reason, identifying α2β1 integrin-specific antagonists can assist in the development of drugs to treat tumor progression, angiogenesis, and cardiovascular diseases. Snake venoms have been shown to contain antagonists which target collagen-binding integrins. EMS16, rhodocetin, and VP12 are three toxins belonging to the C-type lectin-related protein family and have been proven to inhibit the α2β1 integrin, specifically the α2 integrin A domain. To specifically isolate antagonists targeting the α2β1 integrin A domain, we developed a protocol based on affinity chromatography. Using this novel approach, the toxin VP-i was isolated from Vipera palaestinae venom. We show that VP-i binds to the α2 integrin A domain and that it successfully inhibits adhesion of various cells to type I collagen as well as cell migration. Moreover, our results indicate that VP-i differs structurally from the previously purified VP12, although not functionally, and therefore is a further venom compound which can be utilized for drug development.
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http://dx.doi.org/10.1016/j.toxicon.2013.01.001DOI Listing
March 2013

Platelet-derived growth factor triggers PKA-mediated signalling by a redox-dependent mechanism in rat renal mesangial cells.

Biochem Pharmacol 2013 Jan 24;85(1):101-8. Epub 2012 Oct 24.

Pharmazentrum Frankfurt/ZAFES, Klinikum der Johann Wolfgang Goethe-Universität, Frankfurt am Main, Germany.

Inflammatory glomerular kidney diseases are often accompanied with a massive production of reactive oxygen species (ROS) that affect the function of the glomerular filtration barrier and contribute to mesangiolysis via the induction of cell death in mesangial cells. Intriguingly, ROS also trigger fine-tuned signalling processes that affect gene expression and cell proliferation or migration. To define such redox-driven signalling devices, a proteomics approach was performed to identify the formation of protein complexes induced by ROS. To this end, protein lysates of human podocytes were treated with or without hydrogen peroxide (250 μM). Thereafter cell lysates were subjected to diagonal 2D gel electrophoresis and putative redox-affected proteins were analysed by MS/MS analysis. Among others, the regulatory subunit of protein kinase A (PKA) could be identified that forms homodimers under oxidative conditions. To evaluate whether ROS dependent dimerization of PKA also occurs in a more physiological setting, rat mesangial cells were treated with platelet-derived growth factor-BB (PDGF-BB) to induce ROS formation. This regimen resulted in a redox dependent dimerization of the R-subunits of PKA. To demonstrate whether PDGF-BB induced ROS formation affects PKA dependent pathways, the effects of PDGF-BB on phosphorylation of serine 157 of vasodilator stimulated protein (VASP) a classical target of PKA were analysed. Interestingly PDGF-BB induced VASP phosphorylation in a ROS dependent manner but independent of changes in cAMP levels. Taken together, we demonstrate a redox-mediated activation of PKA by PDGF-BB thus highlighting a physiological role of ROS as regulator of PKA activity in rat mesangial cells.
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http://dx.doi.org/10.1016/j.bcp.2012.10.017DOI Listing
January 2013

Xentrivalpeptides A-Q: depsipeptide diversification in Xenorhabdus.

J Nat Prod 2012 Oct 1;75(10):1717-22. Epub 2012 Oct 1.

Institut für Molekulare Biowissenschaften, Goethe Universität Frankfurt, 60438 Frankfurt am Main, Germany.

Seventeen depsipeptides, xentrivalpeptides A-Q (1-17), have been identified from an entomopathogenic Xenorhabdus sp. Whereas the structure of xentrivalpeptide A (1) was determined after its isolation by NMR spectroscopy and the advanced Marfey's method, the structures of all other derivatives were determined using a combination of stable isotope labeling and detailed MS analysis.
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http://dx.doi.org/10.1021/np300279gDOI Listing
October 2012

Complexome profiling identifies TMEM126B as a component of the mitochondrial complex I assembly complex.

Cell Metab 2012 Oct 13;16(4):538-49. Epub 2012 Sep 13.

Molecular Bioenergetics Group, Medical School, Cluster of Excellence Frankfurt Macromolecular Complexes, Goethe University, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany.

Macromolecular complexes are essential players in numerous biological processes. They are often large, dynamic, and rather labile; approaches to study them are scarce. Covering masses up to ∼30 MDa, we separated the native complexome of rat heart mitochondria by blue-native and large-pore blue-native gel electrophoresis to analyze its constituents by mass spectrometry. Similarities in migration patterns allowed hierarchical clustering into interaction profiles representing a comprehensive analysis of soluble and membrane-bound complexes of an entire organelle. The power of this bottom-up approach was validated with well-characterized mitochondrial multiprotein complexes. TMEM126B was found to comigrate with known assembly factors of mitochondrial complex I, namely CIA30, Ecsit, and Acad9. We propose terming this complex mitochondrial complex I assembly (MCIA) complex. Furthermore, we demonstrate that TMEM126B is required for assembly of complex I. In summary, complexome profiling is a powerful and unbiased technique allowing the identification of previously overlooked components of large multiprotein complexes.
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http://dx.doi.org/10.1016/j.cmet.2012.08.009DOI Listing
October 2012

IRES-dependent translation of egr2 is induced under inflammatory conditions.

RNA 2012 Oct 22;18(10):1910-20. Epub 2012 Aug 22.

Institute of Biochemistry I, Goethe-University Frankfurt, 60590 Frankfurt, Germany.

Adjusting translation is crucial for cells to rapidly adapt to changing conditions. While pro-proliferative signaling via the PI3K-mTOR-pathway is known to induce cap-dependent translation, stress conditions, such as nutrient deprivation or hypoxia often activate alternative modes of translation, e.g., via internal ribosome entry sites (IRESs). As the effects of inflammatory conditions on translation are only poorly characterized, we aimed at identifying translationally deregulated targets in inflammatory settings. For this purpose, we cocultured breast tumor cells with conditioned medium of activated monocyte-derived macrophages (CM). Polysome profiling and microarray analysis identified early growth response-2 (egr2) to be regulated at the level of translation. Using bicistronic reporter assays, we found that egr2 contains an IRES within its 5' UTR, which facilitated enhanced translation upon CM treatment. We further provide evidence that the activity of egr2-IRES was induced by IL-1β and p38-MAPK signaling. In addition, we identified several potential IRES trans-acting factors (ITAFs) such as polypyrimidine tract binding protein (PTB) and hnRNP-A1 that directly bind to the egr2-5'UTR. In summary, our data provide evidence that egr2 expression is translationally regulated via an IRES element, which is responsive to an inflammatory environment.
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http://dx.doi.org/10.1261/rna.033019.112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3446713PMC
October 2012

Calpain inhibition stabilizes the platelet proteome and reactivity in diabetes.

Blood 2012 Jul 4;120(2):415-23. Epub 2012 Jun 4.

Institute for Vascular Signalling, Centre for Molecular Medicine, Goethe University, Theodor-Stern-Kai 7, Frankfurt am Main, Germany.

Platelets from patients with diabetes are hyperreactive and demonstrate increased adhesiveness, aggregation, degranulation, and thrombus formation, processes that contribute to the accelerated development of vascular disease. Part of the problem seems to be dysregulated platelet Ca(2+) signaling and the activation of calpains, which are Ca(2+)-activated proteases that result in the limited proteolysis of substrate proteins and subsequent alterations in signaling. In the present study, we report that the activation of μ- and m-calpain in patients with type 2 diabetes has profound effects on the platelet proteome and have identified septin-5 and the integrin-linked kinase (ILK) as novel calpain substrates. The calpain-dependent cleavage of septin-5 disturbed its association with syntaxin-4 and promoted the secretion of α-granule contents, including TGF-β and CCL5. Calpain was also released by platelets and cleaved CCL5 to generate a variant with enhanced activity. Calpain activation also disrupted the ILK-PINCH-Parvin complex and altered platelet adhesion and spreading. In diabetic mice, calpain inhibition reversed the effects of diabetes on platelet protein cleavage, decreased circulating CCL5 levels, reduced platelet-leukocyte aggregate formation, and improved platelet function. The results of the present study indicate that diabetes-induced platelet dysfunction is mediated largely by calpain activation and suggest that calpain inhibition may be an effective way of preserving platelet function and eventually decelerating atherothrombosis development.
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http://dx.doi.org/10.1182/blood-2011-12-399980DOI Listing
July 2012

Integrin α7β1 is a redox-regulated target of hydrogen peroxide in vascular smooth muscle cell adhesion.

Free Radic Biol Med 2012 Aug 31;53(3):521-31. Epub 2012 May 31.

Excellence Cluster Cardio-Pulmonary System, Vascular Matrix Biology, Center for Molecular Medicine, Frankfurt University Hospital, Frankfurt am Main, Germany.

Upon adhesion to laminin-111, aortic smooth muscle cells initially form membrane protrusions with an average diameter of 2.9μm. We identified these protrusions also as subcellular areas of increased redox potential and protein oxidation by detecting cysteine sulfenic acid groups with dimedone. Hence, we termed these areas oxidative hot spots. They are spatially and temporally transient during an early stage of adhesion and depend on the activity of the H(2)O(2)-generating NADPH oxidase 4. Presumably located on cellular protrusions, integrin α7β1 mediates adhesion and migration of vascular smooth muscle cells to laminins of their surrounding basement membrane. Using protein chemistry and mass spectrometry, two specific oxidation sites within the integrin α7 subunit were identified: one located in its genu region and another within its calf 2 domain. Upon H(2)O(2) treatment, two cysteine residues are oxidized thereby unlocking a disulfide bridge. The genu region is a hinge, around which the integrin domains pivot between a bent/inactive and an upright/active conformation. Also, cysteine oxidation within the calf 2 domain permits conformational changes related to integrin activation. H(2)O(2) treatment of α7β1 integrin in concentrations of up to 100μM increases integrin binding activity to laminin-111, suggesting a physiological redox regulation of α7β1 integrin.
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http://dx.doi.org/10.1016/j.freeradbiomed.2012.05.032DOI Listing
August 2012

Protein S-nitrosylation and denitrosylation in the mouse spinal cord upon injury of the sciatic nerve.

J Proteomics 2012 Jul 14;75(13):3987-4004. Epub 2012 May 14.

Institut für Klinische Pharmakologie, Klinikum der Goethe-Universität Frankfurt, 60590 Frankfurt am Main, Germany.

Nitric oxide is a pain signaling molecule and exerts its influence through two primary pathways: by stimulation of soluble guanylylcyclase and by direct S-nitrosylation (SNO) of target proteins. We assessed in the spinal cord the SNO-proteome with two methods, two-dimensional S-nitrosothiol difference gel electrophoresis (2D SNO-DIGE) and SNO-site identification (SNOSID) at baseline and 24h after sciatic nerve injury with/without pretreatment with the nitric oxide synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME). After nerve injury, SNO-DIGE revealed 30 proteins with increased and 23 proteins with decreased S-nitrosylation. SNO-sites were identified for 17 proteins. After sham surgery only 3 proteins were up-nitrosylated. L-NAME pretreatment substantially reduced both constitutive and nerve injury evoked up-S-nitrosylation. For the top candidates S-nitrosylation was confirmed with the biotin switch technique and time course analyses at 1 and 7days showed that SNO modifications of protein disulfide isomerase, glutathione synthase and peroxiredoxin-6 had returned to baseline within 7days whereas S-nitrosylation of mitochondrial aconitase 2 was further increased. The identified SNO modified proteins are involved in mitochondrial function, protein folding and transport, synaptic signaling and redox control. The data show that nitric oxide mediated S-nitrosylation contributes to the nerve injury-evoked pathology in nociceptive signaling pathways.
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http://dx.doi.org/10.1016/j.jprot.2012.05.006DOI Listing
July 2012

Functional dissection of the proton pumping modules of mitochondrial complex I.

PLoS Biol 2011 Aug 23;9(8):e1001128. Epub 2011 Aug 23.

Molecular Bioenergetics Group, Medical School, Cluster of Excellence Frankfurt Macromolecular Complexes, Center for Membrane Proteomics, Johann Wolfgang Goethe-Universität, Frankfurt, Germany.

Mitochondrial complex I, the largest and most complicated proton pump of the respiratory chain, links the electron transfer from NADH to ubiquinone to the pumping of four protons from the matrix into the intermembrane space. In humans, defects in complex I are involved in a wide range of degenerative disorders. Recent progress in the X-ray structural analysis of prokaryotic and eukaryotic complex I confirmed that the redox reactions are confined entirely to the hydrophilic peripheral arm of the L-shaped molecule and take place at a remarkable distance from the membrane domain. While this clearly implies that the proton pumping within the membrane arm of complex I is driven indirectly via long-range conformational coupling, the molecular mechanism and the number, identity, and localization of the pump-sites remains unclear. Here, we report that upon deletion of the gene for a small accessory subunit of the Yarrowia complex I, a stable subcomplex (nb8mΔ) is formed that lacks the distal part of the membrane domain as revealed by single particle analysis. The analysis of the subunit composition of holo and subcomplex by three complementary proteomic approaches revealed that two (ND4 and ND5) of the three subunits with homology to bacterial Mrp-type Na(+)/H(+) antiporters that have been discussed as prime candidates for harbouring the proton pumps were missing in nb8mΔ. Nevertheless, nb8mΔ still pumps protons at half the stoichiometry of the complete enzyme. Our results provide evidence that the membrane arm of complex I harbours two functionally distinct pump modules that are connected in series by the long helical transmission element recently identified by X-ray structural analysis.
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http://dx.doi.org/10.1371/journal.pbio.1001128DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3160329PMC
August 2011

A scaffold of accessory subunits links the peripheral arm and the distal proton-pumping module of mitochondrial complex I.

Biochem J 2011 Jul;437(2):279-88

Medical School, Center for Membrane Proteomics, Goethe-University, Frankfurt am Main, Germany.

Mitochondrial NADH:ubiquinone oxidoreductase (complex I) is a very large membrane protein complex with a central function in energy metabolism. Complex I from the aerobic yeast Yarrowia lipolytica comprises 14 central subunits that harbour the bioenergetic core functions and at least 28 accessory subunits. Despite progress in structure determination, the position of individual accessory subunits in the enzyme complex remains largely unknown. Proteomic analysis of subcomplex Iδ revealed that it lacked eleven subunits, including the central subunits ND1 and ND3 forming the interface between the peripheral and the membrane arm in bacterial complex I. This unexpected observation provided insight into the structural organization of the connection between the two major parts of mitochondrial complex I. Combining recent structural information, biochemical evidence on the assignment of individual subunits to the subdomains of complex I and sequence-based predictions for the targeting of subunits to different mitochondrial compartments, we derived a model for the arrangement of the subunits in the membrane arm of mitochondrial complex I.
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http://dx.doi.org/10.1042/BJ20110359DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3273332PMC
July 2011

Involvement of the Shewanella oneidensis decaheme cytochrome MtrA in the periplasmic stability of the beta-barrel protein MtrB.

Appl Environ Microbiol 2011 Feb 17;77(4):1520-3. Epub 2010 Dec 17.

Universität Freiburg, Institut Biologie II, Mikrobiologie, Schänzlestr. 1, D-79104 Freiburg, Germany.

The Shewanella oneidensis outer membrane β-barrel protein MtrB is part of a membrane-spanning protein complex (MtrABC) which is necessary for dissimilatory iron reduction. Quantitative PCR, heterologous gene expression, and mutant studies indicated that MtrA is required for periplasmic stability of MtrB. DegP depletion compensated for this MtrA dependence.
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http://dx.doi.org/10.1128/AEM.01201-10DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3067208PMC
February 2011
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