12 results on '"Alexander Hempelmann"'
Search Results
2. Nanobody-mediated macromolecular crowding induces membrane fission and remodeling in the African trypanosome
- Author
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Alexander Hempelmann, Laura Hartleb, Monique van Straaten, Hamidreza Hashemi, Johan P. Zeelen, Kevin Bongers, F. Nina Papavasiliou, Markus Engstler, C. Erec Stebbins, and Nicola G. Jones
- Subjects
African trypanosome ,host-pathogen interaction ,variant surface glycoproteins ,immune epitope mapping ,structural biology ,nanovesicle formation ,Biology (General) ,QH301-705.5 - Abstract
Summary: The dense variant surface glycoprotein (VSG) coat of African trypanosomes represents the primary host-pathogen interface. Antigenic variation prevents clearing of the pathogen by employing a large repertoire of antigenically distinct VSG genes, thus neutralizing the host’s antibody response. To explore the epitope space of VSGs, we generate anti-VSG nanobodies and combine high-resolution structural analysis of VSG-nanobody complexes with binding assays on living cells, revealing that these camelid antibodies bind deeply inside the coat. One nanobody causes rapid loss of cellular motility, possibly due to blockage of VSG mobility on the coat, whose rapid endocytosis and exocytosis are mechanistically linked to Trypanosoma brucei propulsion and whose density is required for survival. Electron microscopy studies demonstrate that this loss of motility is accompanied by rapid formation and shedding of nanovesicles and nanotubes, suggesting that increased protein crowding on the dense membrane can be a driving force for membrane fission in living cells.
- Published
- 2021
- Full Text
- View/download PDF
3. The Data Reduction Pipeline of the Hamburg Robotic Telescope
- Author
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Marco Mittag, Alexander Hempelmann, José Nicolás González-Pérez, and Jürgen H. M. M. Schmitt
- Subjects
Astronomy ,QB1-991 - Abstract
The fully automatic reduction pipeline for the blue channel of the HEROS spectrograph of the Hamburg Robotic Telescope (HRT) is presented. This pipeline is started automatically after finishing the night-time observations and calibrations. The pipeline includes all necessary procedures for a reliable and complete data reduction, that is, Bias, Dark, and Flat Field correction. Also the order definition, wavelength calibration, and data extraction are included. The final output is written in a fits-format and ready to use for the astronomer. The reduction pipeline is implemented in IDL and based on the IDL reduction package REDUCE written by Piskunov and Valenti (2002).
- Published
- 2010
- Full Text
- View/download PDF
4. Structure of trypanosome coat protein VSGsur and function in suramin resistance
- Author
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Natalie Wiedemar, F. Nina Papavasiliou, Johan Zeelen, Hamidreza Hashemi, Joseph Verdi, Silvan Hälg, C. Erec Stebbins, Kathryn Perez, Pascal Mäser, Alexander Hempelmann, Philip D. Jeffrey, and Monique van Straaten
- Subjects
Trypanosoma brucei rhodesiense ,Microbiology (medical) ,Protein Conformation ,Suramin ,Immunology ,Drug Resistance ,Plasma protein binding ,Trypanosoma brucei ,Crystallography, X-Ray ,Applied Microbiology and Biotechnology ,Microbiology ,Article ,03 medical and health sciences ,Protein structure ,parasitic diseases ,polycyclic compounds ,Genetics ,medicine ,Antigenic variation ,Binding site ,Immune Evasion ,030304 developmental biology ,chemistry.chemical_classification ,0303 health sciences ,Binding Sites ,biology ,030306 microbiology ,Chemistry ,Cell Biology ,medicine.disease ,biology.organism_classification ,Antigenic Variation ,Trypanocidal Agents ,Endocytosis ,3. Good health ,Cell biology ,Trypanosomiasis, African ,Mutation ,Glycoprotein ,Trypanosomiasis ,Variant Surface Glycoproteins, Trypanosoma ,Protein Binding ,medicine.drug - Abstract
Suramin has been a primary early-stage treatment for African trypanosomiasis for nearly 100 yr. Recent studies revealed that trypanosome strains that express the variant surface glycoprotein (VSG) VSGsur possess heightened resistance to suramin. Here, we show that VSGsur binds tightly to suramin but other VSGs do not. By solving high-resolution crystal structures of VSGsur and VSG13, we also demonstrate that these VSGs define a structurally divergent subgroup of the coat proteins. The co-crystal structure of VSGsur with suramin reveals that the chemically symmetric drug binds within a large cavity in the VSG homodimer asymmetrically, primarily through contacts of its central benzene rings. Structure-based, loss-of-contact mutations in VSGsur significantly decrease the affinity to suramin and lead to a loss of the resistance phenotype. Altogether, these data show that the resistance phenotype is dependent on the binding of suramin to VSGsur, establishing that the VSG proteins can possess functionality beyond their role in antigenic variation. The co-crystal structure of VSGsur with the trypanocidal compound suramin directly links the binding of the drug to the resistance phenotype displayed by strains of Trypanosoma brucei expressing VSGsur. Therefore, VSGs can have a function beyond that of antigenic variation.
- Published
- 2021
5. Rapid, adaptable and sensitive Cas13-based COVID-19 diagnostics using ADESSO
- Author
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Beatrice Casati, Joseph Peter Verdi, Alexander Hempelmann, Maximilian Kittel, Andrea Gutierrez Klaebisch, Bianca Meister, Sybille Welker, Sonal Asthana, Salvatore Di Giorgio, Pavle Boskovic, Ka Hou Man, Meike Schopp, Paul Adrian Ginno, Bernhard Radlwimmer, Charles Erec Stebbins, Thomas Miethke, Fotini Nina Papavasiliou, and Riccardo Pecori
- Subjects
Multidisciplinary ,COVID-19 Testing ,SARS-CoV-2 ,General Physics and Astronomy ,COVID-19 ,Humans ,RNA, Viral ,General Chemistry ,Pandemics ,Sensitivity and Specificity ,General Biochemistry, Genetics and Molecular Biology - Abstract
During the ongoing COVID-19 pandemic, PCR testing and antigen tests have proven critical for helping to stem the spread of its causative agent, SARS-CoV-2. However, these methods suffer from either general applicability and/or sensitivity. Moreover, the emergence of variant strains creates the need for flexibility to correctly and efficiently diagnose the presence of substrains. To address these needs we developed the diagnostic test ADESSO (Accurate Detection of Evolving SARS-CoV-2 through SHERLOCK (Specific High Sensitivity Enzymatic Reporter UnLOCKing) Optimization) which employs Cas13 to diagnose patients in 1 h without sophisticated equipment. Using an extensive panel of clinical samples, we demonstrate that ADESSO correctly identifies infected individuals at a sensitivity and specificity comparable to RT-qPCR on extracted RNA and higher than antigen tests for unextracted samples. Altogether, ADESSO is a fast, sensitive and cheap method that can be applied in a point of care setting to diagnose COVID-19 and can be quickly adjusted to detect new variants.
- Published
- 2021
6. ADESSO: a rapid, adaptable and sensitive Cas13-based COVID-19 diagnostic platform
- Author
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Beatrice Casati, Joseph Peter Verdi, Alexander Hempelmann, Maximilian Kittel, Andrea Gutierrez Klaebisch, Bianca Meister, Sybille Welker, Sonal Asthana, Pavle Boskovic, Ka Hou Man, Meike Schopp, Paul Ginno, Bernhard Radlwimmer, Charles Erec Stebbins, Thomas Miethke, Fotini Nina Papavasiliou, and Riccardo Pecori
- Subjects
education.field_of_study ,Coronavirus disease 2019 (COVID-19) ,Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ,Population ,Diagnostic test ,Gold standard (test) ,Biology ,medicine.disease_cause ,Virology ,medicine ,CRISPR ,education ,Viral load ,Coronavirus - Abstract
With the coronavirus disease 19 (COVID-19) pandemic now deep into its second year, widespread testing for the detection of the causative severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is fundamental. The gold standard reverse transcription quantitative PCR (RT-qPCR) cannot keep up with the high demand alone, therefore alternative diagnostic tests are needed. Here we present ADESSO (Accurate Detection of Evolving SARS-CoV-2 through SHERLOCK Optimisation), an optimised version of the CRISPR-based SHERLOCK (Specific High-sensitivity Enzymatic Reporter unLOCKing) assay. After an extensive validation on 983 clinical samples, we demonstrated that ADESSO has a sensitivity of 96% and a specificity of 100% on extracted RNA, comparable to RT-qPCR. Its performance on unextracted samples still allows the detection of the more infectious 75% of the COVID-19 positive population, making it suitable for point-of-care (POC) testing. Interestingly, our in parallel comparison of 390 matching swab and gargle samples showed consistently lower viral loads in gargle specimens. We also validated ADESSO for the detection of the B.1.1.7 variant and demonstrated that ADESSO is adaptable to any variant of concern in less than one week, a critical feature now that worrisome SARS-CoV-2 variants are spreading all around the world.
- Published
- 2021
7. Nanobody Mediated Macromolecular Crowding Induces Membrane Fission and Remodeling in the African Trypanosome
- Author
-
Hamidreza Hashemi, Laura Hartleb, Johan Zeelen, F. Nina Papavasiliou, Markus Engstler, C. Erec Stebbins, Nicola G. Jones, Monique van Straaten, and Alexander Hempelmann
- Subjects
chemistry.chemical_classification ,biology ,Chemistry ,Motility ,Exocytosis ,Epitope ,Cell biology ,Membrane fission ,parasitic diseases ,biology.protein ,Antigenic variation ,Antibody ,Glycoprotein ,Macromolecular crowding - Abstract
The dense Variant Surface Glycoprotein (VSG) coat of African trypanosomes represents the primary host-pathogen interface. Antigenic variation prevents clearing of the pathogen by employing a large repertoire of antigenically distinct VSG genes, thus neutralizing the host’s antibody response. To explore the epitope space of VSGs, we generated anti-VSG nanobodies and combined high-resolution structural analysis of VSG-nanobody complexes with binding assays on living cells, revealing that these camelid antibodies bind deeply inside the coat. One nanobody caused rapid loss of cellular motility, possibly due to blockage of VSG mobility on the coat, whose rapid endo-and exocytosis is mechanistically linked to T. brucei propulsion and whose density is required for survival. Electron microscopy studies demonstrated that this loss of motility was accompanied by rapid formation and shedding of nanovesicles and nanotubes, suggesting that increased protein crowding on the dense membrane can be a driving force for membrane fission in living cells.
- Published
- 2021
8. Nanobody-mediated macromolecular crowding induces membrane fission and remodeling in the African trypanosome
- Author
-
Alexander, Hempelmann, Laura, Hartleb, Monique, van Straaten, Hamidreza, Hashemi, Johan P, Zeelen, Kevin, Bongers, F Nina, Papavasiliou, Markus, Engstler, C Erec, Stebbins, and Nicola G, Jones
- Subjects
QH301-705.5 ,Trypanosoma brucei brucei ,host-pathogen interaction ,Exocytosis ,Cell Line ,variant surface glycoproteins ,immune epitope mapping ,Epitopes ,Antibody Specificity ,Cell Movement ,ddc:570 ,parasitic diseases ,Animals ,structural biology ,Biology (General) ,nanovesicle formation ,Cell Membrane ,Single-Domain Antibodies ,Trypanocidal Agents ,Endocytosis ,Trypanosomiasis, African ,African trypanosome ,Binding Sites, Antibody ,Camelids, New World ,Variant Surface Glycoproteins, Trypanosoma ,Protein Binding - Abstract
Summary: The dense variant surface glycoprotein (VSG) coat of African trypanosomes represents the primary host-pathogen interface. Antigenic variation prevents clearing of the pathogen by employing a large repertoire of antigenically distinct VSG genes, thus neutralizing the host’s antibody response. To explore the epitope space of VSGs, we generate anti-VSG nanobodies and combine high-resolution structural analysis of VSG-nanobody complexes with binding assays on living cells, revealing that these camelid antibodies bind deeply inside the coat. One nanobody causes rapid loss of cellular motility, possibly due to blockage of VSG mobility on the coat, whose rapid endocytosis and exocytosis are mechanistically linked to Trypanosoma brucei propulsion and whose density is required for survival. Electron microscopy studies demonstrate that this loss of motility is accompanied by rapid formation and shedding of nanovesicles and nanotubes, suggesting that increased protein crowding on the dense membrane can be a driving force for membrane fission in living cells.
- Published
- 2021
9. A Parasite Coat Protein Binds Suramin to Confer Drug Resistance
- Author
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Joseph Verdi, Natalie Wiedemar, Monique van Straaten, Philip D. Jeffrey, Pascal Maeser, Johan Zeelen, F. Nina Papavasiliou, Alexander Hempelmann, Hamidreza Hashemi, Kathryn Perez, Silvan Haelg, and C. Erec Stebbins
- Subjects
chemistry.chemical_classification ,Suramin ,Drug resistance ,Coat protein ,medicine.disease ,Phenotype ,Cell biology ,chemistry ,parasitic diseases ,polycyclic compounds ,medicine ,Antigenic variation ,Parasite hosting ,African trypanosomiasis ,Glycoprotein ,medicine.drug - Abstract
Suramin has been a primary early-stage treatment for African trypanosomiasis for nearly one hundred years. Recent studies revealed that trypanosome strains that express the Variant Surface Glycoprotein VSGsur possess heightened resistance to suramin. We show here that VSGsur binds tightly to suramin, other VSGs do not, and that together with VSG13 it defines a structurally divergent subgroup of these coat proteins. The co-crystal structure of VSGsur with suramin reveals that the chemically symmetric drug binds within a large cavity in the VSG homodimer asymmetrically, primarily through contacts of its central benzene rings. Structure-based, loss-of-contact mutations in VSGsur significantly decrease the affinity to suramin and lead to a loss of the resistance phenotype. Altogether, these data show that the resistance phenotype is dependent on the binding of suramin to VSGsur, establishing that the VSG proteins can possess functionality beyond their role in antigenic variation.
- Published
- 2020
10. Structural Basis of Nanobodies Targeting the Prototype Norovirus
- Author
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Michelle K. Haas, Jessica M. Devant, Kerstin Ruoff, Turgay Kilic, Alessa R. Ringel, Celina Geiss, Grant S. Hansman, Anna D. Koromyslova, Alexander Hempelmann, Juliane Graf, and Imme Roggenbach
- Subjects
Viral protein ,viruses ,Immunology ,Biology ,medicine.disease_cause ,Crystallography, X-Ray ,Microbiology ,Epitope ,Epitopes ,fluids and secretions ,Capsid ,Antigen ,Virology ,Genotype ,medicine ,Escherichia coli ,Binding site ,Caliciviridae Infections ,X-ray crystallography ,chemistry.chemical_classification ,Binding Sites ,Structure and Assembly ,Norovirus ,technology, industry, and agriculture ,virus diseases ,Oligosaccharide ,Single-Domain Antibodies ,chemistry ,Insect Science ,Blood Group Antigens ,Capsid Proteins ,human activities ,Protein Binding - Abstract
The discovery of vulnerable regions on norovirus particles is instrumental in the development of effective inhibitors, particularly for GI noroviruses that are genetically diverse. Analysis of these GI.1-specific Nanobodies has shown that similar to GII norovirus particles, the GI particles have vulnerable regions. The only known cofactor region, the HBGA binding pocket, represents the main target for inhibition. With a combination treatment, i.e., the addition of Nano-7 or Nano-94 with 2′FL, the effect of inhibition was increased. Therefore, combination drug treatments might offer a better approach to combat norovirus infections, especially since the GI genotypes are highly diverse and are continually changing the capsid landscape, and few conserved epitopes have so far been identified., Human norovirus infections are a major disease burden. In this study, we analyzed three new norovirus-specific Nanobodies that interacted with the prototype human norovirus (i.e., genogroup I genotype 1 [GI.1]). We showed that the Nanobodies bound on the side (Nano-7 and Nano-62) and top (Nano-94) of the capsid-protruding (P) domain using X-ray crystallography. Nano-7 and Nano-62 bound at a similar region on the P domain, but the orientations of these two Nanobodies clashed with the shell (S) domain and neighboring P domains on intact particles. This finding suggested that the P domains on the particles should shift in order for Nano-7 and Nano-62 to bind to intact particles. Interestingly, both Nano-7 and Nano-94 were capable of blocking norovirus virus-like particles (VLPs) from binding to histo-blood group antigens (HBGAs), which are important cofactors for norovirus infection. Previously, we showed that the GI.1 HBGA pocket could be blocked with the soluble human milk oligosaccharide 2-fucosyllactose (2′FL). In the current study, we showed that a combined treatment of Nano-7 or Nano-94 with 2′FL enhanced the blocking potential with an additive (Nano-7) or synergistic (Nano-94) effect. We also found that GII Nanobodies with 2′FL also enhanced inhibition. The Nanobody inhibition likely occurred by different mechanisms, including particle aggregation or particle disassembly, whereas 2′FL blocked the HBGA binding site. Overall, these new data showed that the positive effect of the addition of 2′FL was not limited to a single mode of action of Nanobodies or to a single norovirus genogroup. IMPORTANCE The discovery of vulnerable regions on norovirus particles is instrumental in the development of effective inhibitors, particularly for GI noroviruses that are genetically diverse. Analysis of these GI.1-specific Nanobodies has shown that similar to GII norovirus particles, the GI particles have vulnerable regions. The only known cofactor region, the HBGA binding pocket, represents the main target for inhibition. With a combination treatment, i.e., the addition of Nano-7 or Nano-94 with 2′FL, the effect of inhibition was increased. Therefore, combination drug treatments might offer a better approach to combat norovirus infections, especially since the GI genotypes are highly diverse and are continually changing the capsid landscape, and few conserved epitopes have so far been identified.
- Published
- 2019
- Full Text
- View/download PDF
11. Human Norovirus Inhibition through Combination Drug Treatment
- Author
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Michelle K. Haas, Alexander Hempelmann, Alessa Ringel, Jessica Devant, Kerstin Ruoff, Juliane Graf, Celina Geiß, Anna Koromyslova, Turgay Kilic, Imme Roggenbach, and Grant S. Hansman
- Subjects
business.industry ,Biophysics ,Norovirus ,medicine ,medicine.disease_cause ,business ,Virology ,Combination drug - Published
- 2018
12. Mass transfer rate and outburst cycle of SS Cygni
- Author
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Juergen Kurths and Alexander Hempelmann
- Subjects
Physics ,Accretion (meteorology) ,Astrophysics::High Energy Astrophysical Phenomena ,Cataclysmic variable star ,White dwarf ,Astronomy ,Astronomy and Astrophysics ,Astrophysics ,SS Cygni ,Light curve ,Accretion disc ,Space and Planetary Science ,Astrophysics::Solar and Stellar Astrophysics ,Mass transfer rate ,Negative correlation - Abstract
From an analysis of the SS Cygni light curve, we have recently shown (Hempelmann & Kurths 1990) that the rate of mass transfer, M˙ T , from the secondary star to the white dwarf primary is inversely correlated with the outburst cycle, t c . This has been criticized as being of a trivial nature by Cannizzo & Mattei (1992). We demonstrate the nontrivial character of our finding by means of a gedankenexperiment which is based on the static outburst parameters observed. We show in this experiment that a positive M˙ T -t c correlation is possible. The negative correlation found by Hempelmann & Kurths (1990) is a consequence of the dynamics of small and strong outbursts
- Published
- 1993
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