Marquardt, Andreas
E-Mail-Adresse
ORCID
Geburtsdatum
Berufsbeschreibung
Nachname
Vorname
Name
Suchergebnisse Publikationen
The SiaABC threonine phosphorylation pathway controls biofilm formation in response to carbon availability in Pseudomonas aeruginosa
The critical role of bacterial biofilms in chronic human infections calls for novel anti-biofilm strategies targeting the regulation of biofilm development. However, the regulation of biofilm development is very complex and can include multiple, highly interconnected signal transduction/response pathways, which are incompletely understood. We demonstrated previously that in the opportunistic, human pathogen P. aeruginosa, the PP2C-like protein phosphatase SiaA and the di-guanylate cyclase SiaD control the formation of macroscopic cellular aggregates, a type of suspended biofilms, in response to surfactant stress. In this study, we demonstrate that the SiaABC proteins represent a signal response pathway that functions through a partner switch mechanism to control biofilm formation. We also demonstrate that SiaABCD functionality is dependent on carbon substrate availability for a variety of substrates, and that upon carbon starvation, SiaB mutants show impaired dispersal, in particular with the primary fermentation product ethanol. This suggests that carbon availability is at least one of the key environmental cues integrated by the SiaABCD system. Further, our biochemical, physiological and crystallographic data reveals that the phosphatase SiaA and its kinase counterpart SiaB balance the phosphorylation status of their target protein SiaC at threonine 68 (T68). Crystallographic analysis of the SiaA-PP2C domain shows that SiaA is present as a dimer. Dynamic modelling of SiaA with SiaC suggested that SiaA interacts strongly with phosphorylated SiaC and dissociates rapidly upon dephosphorylation of SiaC. Further, we show that the known phosphatase inhibitor fumonisin inhibits SiaA mediated phosphatase activity in vitro. In conclusion, the present work improves our understanding of how P. aeuruginosa integrates specific environmental conditions, such as carbon availability and surfactant stress, to regulate cellular aggregation and biofilm formation. With the biochemical and structural characterization of SiaA, initial data on the catalytic inhibition of SiaA, and the interaction between SiaA and SiaC, our study identifies promising targets for the development of biofilm-interference drugs to combat infections of this aggressive opportunistic pathogen.
The NOX1/4 inhibitor GKT136901 as selective and direct scavenger of peroxynitrite
NADPH oxidases (NOX), catalyzing the reduction of molecular oxygen to form the superoxide radical anion (•O2 -) and hydrogen peroxide (H2O2), are involved in several pathological conditions, such as stroke, diabetes, atherosclerosis, but also in chronic neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, or multiple sclerosis. GKT136901 is a novel NOX-1/4 inhibitor with potential application in the areas of diabetic nephropathy, stroke, or neurodegeneration. In the present study, we investigated additional pharmacological activities of the compound with respect to direct free radical scavenging. GKT136901 did not interact with nitric oxide (•NO), •O2 -, or hydroxyl radicals (•OH), but it acted as selective scavenger of peroxynitrite (PON) already in the submicromolar concentration range. Alpha synuclein (ASYN) is a protein involved in the pathogenesis of Parkinson's disease and a known target for PON-dependent tyrosine nitration. Submicromolar concentrations of GKT136901 prevented tyrosine nitration and di-tyrosine-dependent dimer formation of ASYN by PON as indicated by Western blot and mass spectrometric analysis. GKT136901 itself was degraded when exposed to PON. In a human neuronal cell model, GKT136901 prevented both the depletion of reduced intracellular glutathione, and the degeneration of neurites when present during PON treatment of the cells. When GKT136901 was applied after PON treatment, no protective effect was observed, thus excluding an impact of GKT136901 on cellular death/survival pathways. In summary, selective scavenging of PON is an additional pharmacological property of the NOX-1/4 inhibitor GKT136901, and this may add to the efficiency of the drug in several disease models.
Neuroprotection by Minocycline Caused by Direct and Specific Scavenging of Peroxynitrite
Minocycline prevents oxidative protein modifications and damage in disease models associated with inflammatory glial activation and oxidative stress. Although the drug has been assumed to act by preventing the up-regulation of proinflammatory enzymes, we probed here its direct chemical interaction with reactive oxygen species. The antibiotic did not react with superoxide or •NO radicals, but peroxynitrite (PON) was scavenged in the range of ∼1 μm minocycline and below. The interaction of pharmacologically relevant minocycline concentrations with PON was corroborated in several assay systems and significantly exceeded the efficacy of other antibiotics. Minocycline was degraded during the reaction with PON, and the resultant products lacked antioxidant properties. The antioxidant activity of minocycline extended to cellular systems, because it prevented neuronal mitochondrial DNA damage and glutathione depletion. Maintenance of neuronal viability under PON stress was shown to be solely dependent on direct chemical scavenging by minocycline. We chose α-synuclein (ASYN), known from Parkinsonian pathology as a biologically relevant target in chemical and cellular nitration reactions. Submicromolar concentrations of minocycline prevented tyrosine nitration of ASYN by PON. Mass spectrometric analysis revealed that minocycline impeded nitrations more effectively than methionine oxidations and dimerizations of ASYN, which are secondary reactions under PON stress. Thus, PON scavenging at low concentrations is a novel feature of minocycline and may help to explain its pharmacological activity.
Analysis of the Proteolytic Processing of ABCA3 : Identification of Cleavage Site and Involved Proteases
Rationale
ABCA3 is a lipid transporter in the limiting membrane of lamellar bodies in alveolar type II cells. Mutations in the ABCA3 gene cause respiratory distress syndrome in new-borns and childhood interstitial lung disease. ABCA3 is N-terminally cleaved by an as yet unknown protease, a process believed to regulate ABCA3 activity.
Methods
The exact site where ABCA3 is cleaved was localized using mass spectrometry (MS). Proteases involved in ABCA3 processing were identified using small molecule inhibitors and siRNA mediated gene knockdown. Results were verified by in vitro digestion of a synthetic peptide substrate mimicking ABCA3’s cleavage region, followed by MS analysis.
Results
We found that cleavage of ABCA3 occurs after Lys174 which is located in the proteins’ first luminal loop. Inhibition of cathepsin L and, to a lesser extent, cathepsin B resulted in attenuation of ABCA3 cleavage. Both enzymes showed activity against the ABCA3 peptide in vitro with cathepsin L being more active.
Conclusion
We show here that, like some other proteins of the lysosomal membrane, ABCA3 is a substrate of cathepsin L. Therefore, cathepsin L may represent a potential target to therapeutically influence ABCA3 activity in ABCA3-associated lung disease.
Differentiation of compact and extended conformations of di-ubiquitin conjugates with lysine-specific isopeptide linkages by ion mobility-mass spectrometry
Modification of ubiquitin, a key cellular regulatory polypeptide of 76 amino acids, to polyubiquitin conjugates by lysine-specific isopeptide linkage at one of its seven lysine residues has been recognized as a central pathway determining its biochemical properties and cellular functions. Structural details and differences of distinct lysine-isopeptidyl ubiquitin conjugates that reflect their different functions and reactivities, however, are only partially understood. Ion mobility spectrometry (IMS) combined with mass spectrometry (MS) has recently emerged as a powerful tool for probing conformations and topology involved in protein interactions by an electric field-driven separation of polypeptide ions through a drift gas. Here we report the conformational characterization and differentiation of Lys63- and Lys48-linked ubiquitin conjugates by IMS-MS. Lys63- and Lys48-linked di-ubiquitin conjugates were prepared by recombinant bacterial expression and by chemical synthesis using a specific chemical ligation strategy, and characterized by high-resolution Fourier transform ion cyclotron resonance mass spectrometry, circular dichroism spectroscopy, and molecular modeling. IMS-MS was found to be an effective tool for the identification of structural differences of ubiquitin complexes in the gas phase. The comparison of collision cross-sections of Lys63- and Lys48-linked di-ubiquitin conjugates showed a more elongated conformation of Lys63-linked di-ubiquitin. In contrast, the Lys48-linked di-ubiquitin conjugate showed a more compact conformation. The IMS-MS results are consistent with published structural data and a comparative molecular modeling study of the Lys63- and Lys48-linked conjugates. The results presented here suggest IMS techniques can provide information that complements MS measurements in differentiating higher-order polyubiquitins and other isomeric protein linkages.
Turning the RING domain protein MdmX into an active ubiquitin-protein ligase
The related RING domain proteins MdmX and Mdm2 are best known for their role as negative regulators of the tumor suppressor p53. However, although Mdm2 functions as a ubiquitin ligase for p53, MdmX does not have appreciable ubiquitin ligase activity. In this study, we performed a mutational analysis of the RING domain of MdmX, and we identified two distinct regions that, when replaced by the respective regions of Mdm2, turn MdmX into an active ubiquitin ligase for p53. Mdm2 and MdmX form homodimers as well as heterodimers with each other. One of the regions identified localizes to the dimer interface indicating that subtle conformational changes in this region either affect dimer stability and/or the interaction with the ubiquitin-conjugating enzyme UbcH5b. The second region contains the cryptic nucleolar localization signal of Mdm2 but is also assumed to be involved in the interaction with UbcH5b. Here, we show that this region has a significant impact on the ability of respective MdmX mutants to functionally interact with UbcH5b in vitro supporting the notion that this region serves two distinct functional purposes, nucleolar localization and ubiquitin ligase activity. Finally, evidence is provided to suggest that the RING domain of Mdm2 not only binds to UbcH5b but also acts as an allosteric activator of UbcH5b.
Protein expression profile of HT-29 human colon cancer cells after treatment with a cytotoxic daunorubicin-GnRH-III derivative bioconjugate
Targeted delivery of chemotherapeutic agents is a new approach for the treatment of cancer, which provides increased selectivity and decreased systemic toxicity. We have recently developed a promising drug delivery system, in which the anticancer drug daunorubicin (Dau) was attached via oxime bond to a gonadotropin-releasing hormone-III (GnRH-III) derivative used as a targeting moiety (Glp-His-Trp-Lys(Ac)-His-Asp-Trp-Lys(Dau = Aoa)-Pro-Gly-NH2; Glp = pyroglutamic acid, Ac = acetyl; Aoa = aminooxyacetyl). This bioconjugate exerted in vitro cytostatic/cytotoxic effect on human breast, prostate and colon cancer cells, as well as significant in vivo tumor growth inhibitory effect on colon carcinoma bearing mice. In our previous studies, H-Lys(Dau = Aoa)-OH was identified as the smallest metabolite produced in the presence of rat liver lysosomal homogenate, which was able to bind to DNA in vitro. To get a deeper insight into the mechanism of action of the bioconjugate, changes in the protein expression profile of HT-29 human colon cancer cells after treatment with the bioconjugate or free daunorubicin were investigated by mass spectrometry-based proteomics. Our results indicate that several metabolism-related proteins, molecular chaperons and proteins involved in signaling are differently expressed after targeted chemotherapeutic treatment, leading to the conclusion that the bioconjugate exerts its cytotoxic action by interfering with multiple intracellular processes.
Physical and functional interaction of the HECT ubiquitin-protein ligases E6AP and HERC2
Deregulation of the ubiquitin-protein ligase E6AP contributes to the development of the Angelman syndrome and to cervical carcinogenesis suggesting that the activity of E6AP needs to be under tight control. However, how E6AP activity is regulated at the post-translational level under non-pathologic conditions is poorly understood. In this study, we report that the giant protein HERC2, which is like E6AP a member of the HECT family of ubiquitin-protein ligases, binds to E6AP. The interaction is mediated by the RCC1-like domain 2 of HERC2 and a region spanning amino acid residues 150-200 of E6AP. Furthermore, we provide evidence that HERC2 stimulates the ubiquitin-protein ligase activity of E6AP in vitro and within cells and that this stimulatory effect does not depend on the ubiquitin-protein ligase activity of HERC2. Thus, the data obtained indicate that HERC2 acts as a regulator of E6AP.
Mass spectrometric approaches for elucidation of antigen antibody recognition structures in molecular immunology
Mass spectrometric approaches have recently gained increasing access to molecular immunology and several methods have been developed that enable detailed chemical structure identification of antigen-antibody interactions. Selective proteolytic digestion and MS-peptide mapping (epitope excision) has been successfully employed for epitope identification of protein antigens. In addition, affinity proteomics using partial epitope excision has been developed as an approach with unprecedented selectivity for direct protein identification from biological material. The potential of these methods is illustrated by the elucidation of a β- amyloid plaque-specific epitope recognized by therapeutic antibodies from transgenic mouse models of Alzheimer s disease. Using an immobilized antigen and antibody- proteolytic digestion and analysis by high resolution Fourier transform ion cyclotron resonance mass spectrometry has lead to a new approach for the identification of antibody paratope structures (paratope-excision; parexprot ). In this method, high resolution MS-peptide data at the low ppm level are required for direct identification of paratopes using protein databases. Mass spectrometric epitope mapping and determination of molecular antibody-recognition signatures offer high potential, especially for the development of new molecular diagnostics and the evaluation of new vaccine lead structures.